ALBERT

Description: We present a catalogue of 2D, point spread function-corrected de Vacouleurs, Sérsic, de Vacouleurs+Exponential, and Sérsic+Exponential fits of ~7 x 10 5 spectroscopically selected galaxies drawn from the Sloan Digital Sky Survey (SDSS) Data Release 7. Fits are performed for the SDSS r band utilizing the fitting routine galfit and analysis pipeline pymorph . We compare these fits to prior catalogues. Fits are analysed using a physically motivated flagging system. The flags suggest that more than 90 per cent of two-component fits can be used for analysis. We show that the fits follow the expected behaviour for early and late galaxy types. The catalogues provide a robust set of structural and photometric parameters for future galaxy studies. We show that some biases remain in the measurements, e.g. the presence of bars significantly affect the bulge measurements although the bulge ellipticity may be used to separate barred and non-barred galaxies, and about 15 per cent of bulges of two-component fits are also affected by resolution. The catalogues are available in electronic format. We also provide an interface for generating postage stamp images of the 2D model and residual as well as the 1D profile. These images can be generated for a user-uploaded list of galaxies on demand.

Description: We present new narrow-band (Hα and [O  iii ]) images and optical spectrophotometry of H  ii regions for a gas-rich low-surface-brightness irregular galaxy, KKR 17. The central surface brightness of the galaxy is μ 0 ( B ) = 24.15 ± 0.03 mag s –2 . The galaxy was detected by the Arecibo Legacy Fast ALFA survey (ALFALFA). Its mass is dominated by neutral hydrogen (H  i ) gas. In contrast, both the stellar masses of the bright H  ii and diffuse stellar regions are small. In addition, the fit to the spectral energy distribution to each region shows the stellar populations of H  ii and diffuse regions are different. The bright H  ii region contains a large fraction of O-type stars, revealing recent strong star formation, whereas the diffuse region is dominated by median age stars with a typical age of ~600 Myr. Using McGaugh's abundance model, we found that the average metallicity of KKR 17 is 12 + (O/H) = 8.0 ± 0.1. The star-formation rate of KKR 17 is 0.21 ± 0.04 M  yr –1 , which is ~1/5 of our Milky Way's. Based on the analysis results for young stellar clusters in the H  ii region, the bright H  ii region has two sub-components with different velocities and metallicities. This may be caused by the outflow of massive stars or merging events. However, the mechanism triggering star formation in the H  ii region is still uncertain.

Description: We review the results of the 1988 multiwavelength campaign on the late-type eclipsing binary YY Geminorum. Observations include: broad-band optical and near-infrared photometry, simultaneous optical and ultraviolet ( IUE ) spectroscopy, X-ray ( Ginga ) and radio (VLA) data. From models fitted to the optical light curves, fundamental physical parameters have been determined together with evidence for transient maculations (spots) located near quadrature longitudes and intermediate latitudes. Eclipses were observed at optical, ultraviolet and radio wavelengths. Significant drops in 6 cm radio emission near the phases of both primary and secondary eclipse indicate relatively compact radio emitting volumes that may lie between the binary components. IUE observations during secondary eclipse are indicative of a uniform chromosphere saturated with Mg  ii emission and an extended volume of Lyα emission. Profile fitting of high-dispersion Hα spectra confirms the chromospheric saturation and indicates significant Hα opacity to heights of a few per cent of the photospheric radius. There is evidence for an enhanced Hα emission region visible near phase 0.25–0.35 which may be associated with a large spot on the primary and with two small optical flares which were also observed at other wavelengths: one in microwave radiation and the other in X-rays. For both flares, L X / L opt is consistent with energy release in closed magnetic structures.

Description: To make relevant predictions about observable emission, hydrodynamical simulation codes must employ schemes that account for radiative losses, but the large dimensionality of accurate radiative transfer schemes is often prohibitive. Stamatellos and collaborators introduced a scheme for smoothed particle hydrodynamics (SPH) simulations based on the notion of polytropic pseudo-clouds that uses only local quantities to estimate cooling rates. The computational approach is extremely efficient and works well in cases close to spherical symmetry, such as in star formation problems. Unfortunately, the method, which takes the local gravitational potential as an input, can be inaccurate when applied to non-spherical configurations, limiting its usefulness when studying discs or stellar collisions, among other situations of interest. Here, we introduce the ‘pressure scale height method,’ which incorporates the fluid pressure scaleheight into the determination of column densities and cooling rates, and show that it produces more accurate results across a wide range of physical scenarios while retaining the computational efficiency of the original method. The tested models include spherical polytropes as well as discs with specified density and temperature profiles. We focus on applying our techniques within an SPH code, although our method can be implemented within any particle-based Lagrangian or grid-based Eulerian hydrodynamic scheme. Our new method may be applied in a broad range of situations, including within the realm of stellar interactions, collisions, and mergers.

Description: We measure and quantify properties of galactic outflows and diffuse gas at z ≥ 1 in cosmological hydrodynamical simulations. Our novel subresolution model, Multi-Phase Particle Integrator (MUPPI), implements supernova feedback using fully local gas properties, where the wind velocity and mass loading are not given as input. We find the following trends at z  = 2 by analysing central galaxies having a stellar mass higher than 10 9 M . The outflow velocity and mass outflow rate ( $\dot{M}_{\rm out}$ ) exhibit positive correlations with galaxy mass and with the star formation rate (SFR). However, most of the relations present a large scatter. The outflow mass loading factor () is between 0.2 and 10. The comparison effective model generates a constant outflow velocity, and a negative correlation of with halo mass. The number fraction of galaxies where outflow is detected decreases at lower redshifts, but remains more than 80 per cent over z  = 1–5. The outflow velocity correlation with SFR becomes flatter at z  = 1, and displays a negative correlation with halo mass in massive galaxies. Our study demonstrates that both the MUPPI and effective models produce significant outflows at ~1/10 of the virial radius; at the same time shows that the properties of outflows generated can be different from the input speed and mass loading in the effective model. Our MUPPI model, using local properties of gas in the subresolution recipe, is able to develop galactic outflows whose properties correlate with global galaxy properties , and consistent with observations.

Description: Long-duration gamma-ray bursts (GRBs) are thought to come from the core collapse of Wolf–Rayet stars. Whereas their stellar masses M * have a rather narrow distribution, the population of GRBs is very diverse, with gamma-ray luminosities L spanning several orders of magnitude. This suggests the existence of a ‘hidden’ stellar variable whose burst-to-burst variation leads to a spread in L . Whatever this hidden variable is, its variation should not noticeably affect the shape of GRB light curves, which display a constant luminosity (in a time-average sense) followed by a sharp drop at the end of the burst seen with Swift /XRT. We argue that such a hidden variable is progenitor star's large-scale magnetic flux. Shortly after the core collapse, most of stellar magnetic flux accumulates near the black hole (BH) and remains there. The flux extracts BH rotational energy and powers jets of roughly a constant luminosity, L j . However, once BH mass accretion rate $\dot{M}$ falls below ~ L j / c 2 , the flux becomes dynamically important and diffuses outwards, with the jet luminosity set by the rapidly declining mass accretion rate, $L_{\rm j}\sim \dot{M}c^2$ . This provides a potential explanation for the sharp end of GRBs and the universal shape of their light curves. During the GRB, gas infall translates spatial variation of stellar magnetic flux into temporal variation of L j . We make use of the deviations from constancy in L j to perform stellar magnetic flux ‘tomography’. Using this method, we infer the presence of magnetized tori in the outer layers of progenitor stars for GRB 920513 and GRB 940210.

Description: We make use of a large set of fast simulations of an intensity mapping experiment with characteristics similar to those expected of the Square Kilometre Array in order to study the viability and limits of blind foreground subtraction techniques. In particular, we consider three different approaches: polynomial fitting, principal component analysis (PCA) and independent component analysis (ICA). We review the motivations and algorithms for the three methods, and show that they can all be described, using the same mathematical framework, as different approaches to the blind source separation problem. We study the efficiency of foreground subtraction both in the angular and radial (frequency) directions, as well as the dependence of this efficiency on different instrumental and modelling parameters. For well-behaved foregrounds and instrumental effects, we find that foreground subtraction can be successful to a reasonable level on most scales of interest. We also quantify the effect that the cleaning has on the recovered signal and power spectra. Interestingly, we find that the three methods yield quantitatively similar results, with PCA and ICA being almost equivalent.

Description: Observed galaxies with high stellar masses or in dense environments have low specific star formation rates, i.e. they are quenched. Based on cosmological hydrodynamic simulations that include a prescription where quenching occurs in regions dominated by hot (〉10 5.4  K) gas, we argue that this hot gas quenching in haloes 〉10 12 M drives both mass quenching (i.e. central quenching) and environment quenching (i.e. satellite quenching). These simulations reproduce a broad range of locally observed trends among quenching, halo mass, stellar mass, environment, and distance to halo centre. Mass quenching is independent of environment because ~10 12 –10 13 M ‘mass quenching haloes’ inhabit a large range of environments. On the other hand, environment quenching is independent of stellar mass because galaxies of all stellar masses may live in dense environments as satellites of groups and clusters. As in observations, the quenched fraction of satellites increases with halo mass and decreases with distance to the centre of the group or cluster. We investigate pre-processing in group haloes, ejected former satellites, and hot gas that extends beyond the virial radius. The agreement of our model with key observational trends suggests that hot gas in massive haloes plays a leading role in quenching low-redshift galaxies.

Description: We used Arecibo Observatory and the Green Bank Telescope to observe OH in 12 early-type galaxies with known reservoirs of dense gas. We present three new detections of OH in absorption in the 1667 MHz line. One objective of our survey was to find evidence of molecular outflows, but our sensitivity and the strength of the OH absorption were insufficient to detect outflows. The detected sources have infrared luminosities and dust temperatures among the lowest of any galaxy detected in OH absorption. The ratio L HCN / L CO , a measure of the dense gas fraction in galaxies, is a powerful selector of OH megamasers for galaxies with high infrared luminosity. In early-type galaxies, which have much lower infrared luminosities, L HCN / L CO is also a promising tool for discovering OH, but in absorption rather than in maser emission. In addition to dense molecular gas, a radio continuum source and a favourable line of sight to the observer are likely key factors in detecting OH absorbers.

Description: The initial mass function (IMF) of the Arches cluster, which was formed a few million years ago in the harsh environment of the Galactic Centre (GC), has long been a target of interest to those who study the GC and the theory of star formation. The distinct star-forming conditions in the GC might have caused the cluster to have a shallower slope or an elevated lower mass cutoff in its IMF. But its mass function (MF) has been revealed only down to 1–2 M (the lower limit of resolved stars), and the low-end MF of the Arches is still unknown. To estimate the unresolved part of the Arches MF, we have devised a novel photometric method that involves the histogram of pixel intensities in the observed image, which contains information on the unresolved, faint stars. By comparing the pixel intensity histograms (PIHs) of numerous artificial images constructed from model IMFs with the observed PIH, we find that the best-fitting model IMF for the Arches cluster has a cutoff mass less than or similar to 0.1 M and a shape very close to that of the Kroupa MF. Our findings imply that the IMF of the Arches cluster is similar to those found in the Galactic disc.

Description: Polarization in classical Be stars results from Thomson scattering of the unpolarized light from the Be star in the circumstellar disc. Theory and observations agree that the maximum degree of polarization from isolated Be stars is 4 per cent. We report on the first optical polarimetric observations of the Be/X-ray binary EXO 2030+375. We find that the optical ( R -band) light is strongly linearly polarized with a degree of polarization of 19 per cent, the highest ever measured either in a classical or Be/X-ray binary. We argue that the interstellar medium cannot account for this high-polarization degree and that a substantial amount must be intrinsic to the source. We propose that it may result from the alignment of non-spherical ferromagnetic grains in the Be star disc due to the strong neutron star magnetic field.

Description: We present two estimators to quantify the angular power spectrum of the sky signal directly from the visibilities measured in radio interferometric observations. This is relevant for both the foregrounds and the cosmological 21-cm signal buried therein. The discussion here is restricted to the Galactic synchrotron radiation, the most dominant foreground component after point source removal. Our theoretical analysis is validated using simulations at 150 MHz, mainly for GMRT and also briefly for Low-Frequency Array. The Bare Estimator uses pairwise correlations of the measured visibilities, while the Tapered Gridded Estimator uses the visibilities after gridding in the uv plane. The former is very precise, but computationally expensive for large data. The latter has a lower precision, but takes less computation time which is proportional to the data volume. The latter also allows tapering of the sky response leading to sidelobe suppression, an useful ingredient for foreground removal. Both estimators avoid the positive bias that arises due to the system noise. We consider amplitude and phase errors of the gain, and the w -term as possible sources of errors. We find that the estimated angular power spectrum is exponentially sensitive to the variance of the phase errors but insensitive to amplitude errors. The statistical uncertainties of the estimators are affected by both amplitude and phase errors. The w -term does not have a significant effect at the angular scales of our interest. We propose the Tapered Gridded Estimator as an effective tool to observationally quantify both foregrounds and the cosmological 21-cm signal.

Description: We extend the theory of astrophysical maser propagation through a medium with a Zeeman-split molecular response to the case of a non-uniform magnetic field, and allow a component of the electric field of the radiation in the direction of propagation: a characteristic of radiation with orbital angular momentum. A classical reduction of the governing equations leads to a set of nine differential equations for the evolution of intensity-like parameters for each Fourier component of the radiation. Four of these parameters correspond to the standard Stokes parameters, whilst the other five represent the z -component of the electric field, and its coupling to the conventional components in the x – y -plane. A restricted analytical solution of the governing equations demonstrates a non-trivial coupling of the Stokes parameters to those representing orbital angular momentum: the z -component of the electric field can grow from a background in which only Stokes- I is non-zero. A numerical solution of the governing equations reveals radiation patterns with a radial and angular structure for the case of an ideal quadrupole magnetic field perpendicular to the propagation direction. In this ideal case, generation of radiation orbital angular momentum, like polarization, can approach 100 per cent.

Description: A halo merger tree forms the essential backbone of a semi-analytic model for galaxy formation and evolution. Recent studies have pointed out that extracting merger trees from numerical simulations of structure formation is non-trivial; different tree building algorithms can give differing merger histories. These differences should be carefully understood before merger trees are used as input for models of galaxy formation. We investigate the impact of different halo merger trees on a semi-analytic model. We find that the z  = 0 galaxy properties in our model show differences between trees when using a common parameter set. The star formation history of the universe and the properties of satellite galaxies can show marked differences between trees with different construction methods. Independently calibrating the semi-analytic model for each tree can reduce the discrepancies between the z  = 0 global galaxy properties, at the cost of increasing the differences in the evolutionary histories of galaxies. Furthermore, the underlying physics implied can vary, resulting in key quantities such as the supernova feedback efficiency differing by factors of 2. Such a change alters the regimes where star formation is primarily suppressed by supernovae. Therefore, halo merger trees extracted from a common halo catalogue using different, but reliable, algorithms can result in a difference in the semi-analytic model. Given the uncertainties in galaxy formation physics, however, these differences may not necessarily be viewed as significant.

Description: We simulate the evolution of dense-cool clumps embedded in the intracluster medium (ICM) of cooling flow clusters of galaxies in response to multiple jet-activity cycles, and find that the main heating process of the clumps is mixing with the hot shocked jets’ gas, the bubbles, while shocks have a limited role. We use the pluto hydrodynamical code in two dimensions with imposed axisymmetry, to follow the thermal evolution of the clumps. We find that the inflation process of hot bubbles, which appear as X-ray deficient cavities in observations, is accompanied by complicated induced vortices inside and around the bubbles. The vorticity induces efficient mixing of the hot bubbles’ gas with the ICM and cool clumps, resulting in a substantial increase of the temperature and entropy of the clumps. For the parameters used by us, heating by shocks barely competes with radiative cooling, even after 25 consecutive shocks excited during 0.5 Gyr of simulation. Some clumps are shaped to filamentary structure that can turn to observed optical filaments. We find that not all clumps are heated. Those that cool to very low temperatures will fall in and feed the central supermassive black hole, hence closing the feedback cycle in what is termed the cold feedback mechanism.

Description: The pulsar IGR J16393–4643 belongs to a class of highly absorbed supergiant high-mass X-ray binaries (HMXBs), characterized by a very high column density of absorbing matter. We present the results of simultaneous broad-band pulsation and spectrum analysis from a 44-ks Suzaku observation of the source. The orbital intensity profile created with the Swift Burst Alert Telescope ( Swift –BAT) light curve shows an indication of IGR J16393–4643 being an eclipsing system with a short eclipse semi-angle E  ~ 17°. For a supergiant companion star with a 20-R radius, this implies an inclination of the orbital plane in the range 39°–57°, whereas for a main-sequence B star as the companion with a 10-R radius, the inclination of the orbital plane is in the range 60°–77°. Pulse profiles created for different energy bands have complex morphology, which shows some energy dependence and increases in pulse fraction with energy. We have also investigated broad-band spectral characteristics, phase-averaged spectra and resolving the pulse phase into peak and trough phases. The phase-averaged spectrum has a very high N H (~ 3 10 23  cm –2 ) and is described by a power law ( ~ 0.9) with a high-energy cut-off above 20 keV. We find a change in the spectral index in the peak and trough phases, implying an underlying change in the source spectrum.

Description: A large class of flat axially symmetric solutions to the Vlasov–Poisson system is constructed with the property that the corresponding rotation curves are approximately flat, slightly decreasing or slightly increasing. The rotation curves are compared with measurements from real galaxies and satisfactory agreement is obtained. These facts raise the question whether the observed rotation curves for disc galaxies may be explained without introducing dark matter. Furthermore, it is shown that for the ansatz we consider stars on circular orbits do not exist in the neighbourhood of the boundary of the steady state.

Description: This paper presents a detailed analysis of two-armed spiral structure in a sample of galaxies from the Spitzer Infrared Nearby Galaxies Survey, with particular focus on the relationships between the properties of the spiral pattern in the stellar disc and the global structure and environment of the parent galaxies. Following Paper I , we have used a combination of Spitzer Space Telescope mid-infrared imaging and visible multicolour imaging to isolate the spiral pattern in the underlying stellar discs, and we examine the systematic behaviours of the observed amplitudes and shapes (pitch angles) of these spirals. In general, spiral morphology is found to correlate only weakly at best with morphological parameters such as stellar mass, gas fraction, disc/bulge ratio, and v flat . In contrast to weak correlations with galaxy structure, a strong link is found between the strength of the spiral arms and tidal forcing from nearby companion galaxies. This appears to support the longstanding suggestion that either a tidal interaction or strong bar is a necessary condition for driving grand-design spiral structure. The pitch angles of the stellar arms are only loosely correlated with the pitch angles of the corresponding arms traced in gas and young stars. We find that the strength of the shock in the gas and the contrast in the star formation rate are strongly correlated with the stellar spiral amplitude.

Description: We combine photometry from the Ultra Deep Survey (UDS), Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) UDS and CANDELS the Great Observatories Origins Deep Survey-South (GOODS-S) surveys to construct the galaxy stellar mass function probing both the low- and high-mass end accurately in the redshift range 0.3 〈  z  〈 3. The advantages of using a homogeneous concatenation of these data sets include meaningful measures of environment in the UDS, due to its large area (0.88 deg 2 ), and the high-resolution deep imaging in CANDELS ( H 160  〉 26.0), affording us robust measures of structural parameters. We construct stellar mass functions for the entire sample as parametrized by the Schechter function, and find that there is a decline in the values of and of α with higher redshifts, and a nearly constant M * up to z  ~ 3. We divide the galaxy stellar mass function by colour, structure, and environment and explore the links between environmental overdensity, morphology, and the quenching of star formation. We find that a double Schechter function describes galaxies with high Sérsic index ( n  〉 2.5), similar to galaxies which are red or passive. The low-mass end of the n  〉 2.5 stellar mass function is dominated by blue galaxies, whereas the high-mass end is dominated by red galaxies. This shows that there is a possible link between morphological evolution and star formation quenching in high mass galaxies, which is not seen in lower mass systems. This in turn suggests that there are strong mass-dependent quenching mechanisms. In addition, we find that the number density of high-mass systems is elevated in dense environments, suggesting that an environmental process is building up massive galaxies quicker in over densities than in lower densities.

Description: We analyse a sample of 26 active galactic nuclei (AGN) with deep XMM–Newton observations, using principal component analysis (PCA) to find model-independent spectra of the different variable components. In total, we identify at least 12 qualitatively different patterns of spectral variability, involving several different mechanisms, including five sources which show evidence of variable relativistic reflection (MCG–6-30-15, NGC 4051, 1H 0707–495, NGC 3516 and Mrk 766) and three which show evidence of varying partial covering neutral absorption (NGC 4395, NGC 1365 and NGC 4151). In over half of the sources studied, the variability is dominated by changes in a power-law continuum, both in terms of changes in flux and power-law index, which could be produced by propagating fluctuations within the corona. Simulations are used to find unique predictions for different physical models, and we then attempt to qualitatively match the results from the simulations to the behaviour observed in the real data. We are able to explain a large proportion of the variability in these sources using simple models of spectral variability, but more complex models may be needed for the remainder. We have begun the process of building up a library of different principal components, so that spectral variability in AGN can quickly be matched to physical processes. We show that PCA can be an extremely powerful tool for distinguishing different patterns of variability in AGN, and that it can be used effectively on the large amounts of high-quality archival data available from the current generation of X-ray telescopes. We will make our PCA code available upon request to the lead author.

Description: Using N -body simulations we study the phenomenon of radial orbit instability occurring in dark matter haloes of the size of a dwarf galaxy. We carried out simulations of seven spherical models, with the same standard NFW (Navarro, Frenk & White) density profile but different anisotropy profiles of particle orbits. Four of them underwent instability: two with a constant positive anisotropy, one with an anisotropic core and an isotropic envelope and one with a very small isotropic core and an anisotropic envelope. Haloes affected by the instability become approximately axisymmetric and prolate, with the profile of the shortest-to-longest axis ratio increasing with radius. The lower limit for the central value of this axis ratio is 0.3 for an NFW halo. The density profiles of the haloes did not change significantly, whereas the velocity distributions became axisymmetric. The angular momentum modulus rose due to large-amplitude oscillations of its components perpendicular to the symmetry axis of the halo. We also studied orbits of individual particles assigning them to classical orbit families in triaxial potentials. We find that the membership of a given particle in a family depends on its initial angular momentum modulus and its components along the principal axes of matter distribution.

Description: We present a study of the prevalence and luminosity of active galactic nuclei (AGN; traced by optical spectra) as a function of both environment and galaxy interactions. For this study, we used a sample of more than 250 000 galaxies drawn from the Sloan Digital Sky Survey and, crucially, we controlled for the effect of both stellar mass and central star formation activity. Once these two factors are taken into account, the effect of the local density of galaxies and of one-on-one interactions is minimal in both the prevalence of AGN activity and AGN luminosity. This suggests that the level of nuclear activity depends primarily on the availability of cold gas in the nuclear regions of galaxies and that secular processes can drive the AGN activity in the majority of cases. Large-scale environment and galaxy interactions only affect AGN activity in an indirect manner, by influencing the central gas supply.

Description: We report the results of the photometric and spectroscopic monitoring campaign of the transient SN 2007sv. The observables are similar to those of Type IIn supernovae, a well-known class of objects whose ejecta interact with pre-existing circumstellar material (CSM). The spectra show a blue continuum at early phases and prominent Balmer lines in emission; however, the absolute magnitude at the discovery of SN 2007sv ( M R  = –14.25 ± 0.38) indicate it to be most likely a supernova impostor. This classification is also supported by the lack of evidence in the spectra of very high velocity material as expected in supernova ejecta. In addition, we find no unequivocal evidence of broad lines of α- and/or Fe-peak elements. The comparison with the absolute light curves of other interacting objects (including Type IIn supernovae) highlights the overall similarity with the prototypical impostor SN 1997bs. This supports our claim that SN 2007sv was not a genuine supernova, and was instead a supernova impostor, most likely similar to the major eruption of a luminous blue variable.

Description: The Cosmicflows-2 catalogue is a compendium of peculiar velocity measurements. While it has many objects in common with the COMPOSITE catalogue, a previously analysed collection of peculiar velocity data found to give an unexpectedly large bulk flow on large scales, the data in Cosmicflows-2 have been reanalysed to ensure consistency between distances measured using different methods. In particular, a focus on accurate distances led the authors of the Cosmicflows-2 to not correct for homogeneous or inhomogeneous Malmquist bias, both or which are corrected for in the COMPOSITE compilation. We find remarkable agreement between the COMPOSITE and the Cosmicflows-2 if the small EFAR sample of clusters located in two dense superclusters is removed from both surveys, giving results that are inconsistent with the cold dark matter standard model with Planck central parameters at the 98 per cent level. On smaller scales we find overall agreement between data sets and consistency with the standard model.

Description: We quantify the stellar abundances of neutron-rich r-process nuclei in cosmological zoom-in simulations of a Milky Way-mass galaxy from the Feedback In Realistic Environments project. The galaxy is enriched with r-process elements by binary neutron star (NS) mergers and with iron and other metals by supernovae. These calculations include key hydrodynamic mixing processes not present in standard semi-analytic chemical evolution models, such as galactic winds and hydrodynamic flows associated with structure formation. We explore a range of models for the rate and delay time of NS mergers, intended to roughly bracket the wide range of models consistent with current observational constraints. We show that NS mergers can produce [r-process/Fe] abundance ratios and scatter that appear reasonably consistent with observational constraints. At low metallicity, [Fe/H]  –2, we predict there is a wide range of stellar r-process abundance ratios, with both supersolar and subsolar abundances. Low-metallicity stars or stars that are outliers in their r-process abundance ratios are, on average, formed at high redshift and located at large galactocentric radius. Because NS mergers are rare, our results are not fully converged with respect to resolution, particularly at low metallicity. However, the uncertain rate and delay time distribution of NS mergers introduce an uncertainty in the r-process abundances comparable to that due to finite numerical resolution. Overall, our results are consistent with NS mergers being the source of most of the r-process nuclei in the Universe.

Description: We present time series spectroscopy of two short period cataclysmic variables, CC Scl and V2051 Oph, to test the efficiency of Doppler-tomography-based methods in constraining orbital parameters of evolved cataclysmic variables. We find that the Ca ii triplet lines offer superior diagnostics, revealing emission components from the mass donors and sharp images of the accretion discs. Furthermore, we use Monte Carlo methods to estimate the uncertainties from ensembles of Doppler maps. We compare our new methods against traditional radial velocity methods and show that they offer a valid route towards system parameter determination. Our analysis of CC Scl suggests a low mass ratio of q  = 0.08 ± 0.03 with a primary velocity of K 1  = 37 ± 14 km s –1 . This mass ratio is in between the pre- and post-period minimum status, however our K 1 solution favours a post-period minimum system. Our derived parameters for V2051 Oph ( q  = 0.18 ± 0.05, K 1  = 97 ± 10 km s –1 ) are in agreement with the eclipse solution ( q  = 0.19 ± 0.03), offering a direct validation of our methods.

Description: We present NuSTAR observations of the bright Seyfert 2 galaxy NGC 2110 obtained in 2012, when the source was at the highest flux level ever observed, and in 2013, when the source was at a more typical flux level. We include archival observations from other X-ray satellites, namely XMM–Newton , Suzaku , BeppoSAX , Chandra and Swift . Simultaneous NuSTAR and Swift broad-band spectra (in the 3–80 keV range) indicate a cutoff energy E c  〉 210 keV, with no detectable contribution from Compton reflection. NGC 2110 is one of the very few sources where no evidence for distant Compton-thick scattering is found and, by using temporal information collected over more than a decade, we investigate variations of the iron Kα line on time-scales of years. The Fe Kα line is likely the sum of two components: one constant (originating from distant Compton-thick material) and the other one variable and linearly correlated with the source flux (possibly arising from Compton-thin material much closer to the black hole).

Description: Polycyclic aromatic hydrocarbons (PAHs) are believed to be the small-size tail of the interstellar carbonaceous dust grain population. Their vibrational emission is the most widely accepted source of the aromatic near-infrared features, and their rotational radiation is a likely explanation for the dust-correlated anomalous microwave emission (AME). Yet, no individual interstellar PAH molecule has been identified to date. It was recently recognized that quasi-symmetric planar PAHs ought to have a well identifiable comb-like rotational spectrum, and suggested to search for them in spectroscopic data with matched-filtering techniques. We report the results of the first such search, carried out with the Green Bank Telescope, and targeting the star-forming region IC 348 in the Perseus molecular cloud, a known source of AME. Our observations amounted to 16.75 h and spanned a 3-GHz-wide band extending from 23.3 to 26.3 GHz. Using frequency switching, we achieved a sensitivity of 0.4 mJy per 0.4 MHz channel (1). The non-detection of comb-like spectra allowed us to set upper bounds on the abundance of specific quasi-symmetric PAH molecules (specified uniquely by their moments of inertia) of approximately 0.1 per cent of the total PAH abundance. This bound generically applies to PAHs with approximately 15–100 carbon atoms.

Description: As is well known, it is necessary to derive stellar parameters from massive amounts of spectral data automatically and efficiently. However, in traditional automatic methods such as artificial neural networks (ANNs) and kernel regression (KR), it is often difficult to optimize the algorithm structure and determine the optimal algorithm parameters. Gaussian process regression (GPR) is a recently developed method that has been proven to be capable of overcoming these difficulties. Here we apply GPR to derive stellar atmospheric parameters from spectra. Through evaluating the performance of GPR on Sloan Digital Sky Survey (SDSS) spectra, Medium resolution Isaac Newton Telescope Library of Empirical Spectra (MILES) spectra, ELODIE spectra and the spectra of member stars of galactic globular clusters, we conclude that GPR can derive stellar parameters accurately and precisely, especially when we use data preprocessed with principal component analysis (PCA). We then compare the performance of GPR with that of several widely used regression methods (ANNs, support-vector regression and KR) and find that with GPR it is easier to optimize structures and parameters and more efficient and accurate to extract atmospheric parameters.

Description: Galaxy–galaxy weak lensing is a direct probe of the mean matter distribution around galaxies. The depth and sky coverage of the Canada–France–Hawaii Telescope Legacy Survey yield statistically significant galaxy halo mass measurements over a much wider range of stellar masses (10 8.75 to 10 11.3 M ) and redshifts (0.2 〈  z  〈 0.8) than previous weak lensing studies. At redshift z  ~ 0.5, the stellar-to-halo mass ratio (SHMR) reaches a maximum of 4.0 ± 0.2 per cent as a function of halo mass at ~10 12.25 M . We find, for the first time from weak lensing alone, evidence for significant evolution in the SHMR: the peak ratio falls as a function of cosmic time from 4.5 ± 0.3 per cent at z  ~ 0.7 to 3.4 ± 0.2 per cent at z  ~ 0.3, and shifts to lower stellar mass haloes. These evolutionary trends are dominated by red galaxies, and are consistent with a model in which the stellar mass above which star formation is quenched ‘downsizes’ with cosmic time. In contrast, the SHMR of blue, star-forming galaxies is well fitted by a power law that does not evolve with time. This suggests that blue galaxies form stars at a rate that is balanced with their dark matter accretion in such a way that they evolve along the SHMR locus. The redshift dependence of the SHMR can be used to constrain the evolution of the galaxy population over cosmic time.

Description: We present 1000 mock galaxy catalogues (mocks) for the analysis of the low-redshift sample (LOWZ; effective redshift z  ~ 0.32) of the Baryon Oscillation Spectroscopic Survey (BOSS) Data Releases 10 and 11. These mocks have been created following the PTHalos method revised to include new developments. The main improvement is the introduction of a redshift dependence in the halo occupation distribution in order to account for the change of the galaxy number density with redshift. These mock galaxy catalogues are used in the analyses of the LOWZ galaxy clustering by the BOSS collaboration.

Description: We present two new catalogues of superclusters of galaxies out to a redshift of z  = 0.15, based on the Abell/ACO cluster redshift compilation maintained by one of us (HA). The first of these catalogues, the all-sky Main SuperCluster Catalogue (MSCC), is based on only the rich (A-) Abell clusters, and the second one, the Southern SuperCluster Catalogue (SSCC), covers declinations  〈 –17° and includes the supplementary Abell S-clusters. A tunable Friends-of-Friends algorithm was used to account for the cluster density decreasing with redshift and for different selection functions in distinct areas of the sky. We present the full list of Abell clusters used, together with their redshifts and supercluster memberships and including the isolated clusters. The SSCC contains about twice the number of superclusters than MSCC for  〈 –17°, which we found to be due to (1) new superclusters formed by A-clusters in their cores and surrounded by S-clusters (50 per cent), (2) new superclusters formed by S-clusters only (40 per cent), (3) redistribution of member clusters by fragmentation of rich (multiplicity m 〉 15) superclusters (8 per cent), and (4) new superclusters formed by the connection of A-clusters through bridges of S-clusters (2 per cent). Power-law fits to the cumulative supercluster multiplicity function yield slopes of α = –2.0 and α = –1.9 for MSCC and SSCC, respectively. This power-law behaviour is in agreement with the findings for other observational samples of superclusters, but not with that of catalogues based on cosmological simulations.

Description: We use two cosmological simulations of structure formation in the cold dark matter (CDM) scenario to study the evolutionary histories of dark matter haloes and to characterize the Lagrangian regions from which they form. We focus on haloes identified at redshift z id  = 0 and show that the classic ellipsoidal collapse model systematically overestimates their collapse times. If one imposes that halo collapse takes place at z id , this model requires starting from a significantly lower linear density contrast than what is measured in the simulations at the locations of halo formation. We attempt to explain this discrepancy by testing two key assumptions of the model. First, we show that the tides felt by collapsing haloes due to the surrounding large-scale structure evolve non-linearly. Although this effect becomes increasingly important for low-mass haloes, accounting for it in the ellipsoidal collapse model only marginally improves the agreement with N -body simulations. Second, we track the time evolution of the physical volume occupied by forming haloes and show that, after turnaround, it generally stabilizes at a well-defined redshift, z c  〉  z id , contrary to the basic assumption of extended Press–Schechter theory based on excursion sets. We discuss the implications of this result for understanding the origin of the mass dependence and scatter in the linear threshold for halo formation. Finally, we show that, when tuned for collapse at z c , a modified version of the ellipsoidal collapse model that also accounts for the triaxial nature of protohaloes predicts their linear density contrast in an unbiased way.

Description: The polarimetric measurement on the prompt phase of GRB 100826A shows that the polarization angle changes ~90° between two adjacent time intervals. We will show that this phenomenon can be naturally interpreted in the framework of the magnetic-dominated jet (MDJ) model. The MDJ model suggests that the bulk Lorentz factor of the outflow increases as r 1/3 , until reaching a saturated value sat . Electrons move in the globally ordered magnetic field advected by the jet from the central engine and produce synchrotron photons. The polarized synchrotron photons travel alone the jet direction and then collide with the cold electrons at the front of the jet. After the Compton scattering process, these photons escape from the jet and are detected by the observer locating slightly off-axis. If photons are emitted before the bulk Lorentz factor saturates, the change of polarization angle is a natural result of the acceleration of the outflow.

Description: The origin of trace hydrogen in white dwarfs (WDs) with He-dominated atmospheres is a long-standing problem, one that cannot satisfactorily be explained by the historically favoured hypothesis of accretion from the interstellar medium. Here we explore the possibility that the gradual accretion of exo-Oort cloud comets, which are a rich source of H, contributes to the apparent increase of trace H with WD cooling age. We determine how often remnant exo-Oort clouds, freshly excited from post-main-sequence stellar mass loss, dynamically inject comets inside the WD's Roche radius. We improve upon previous studies by considering a representative range of single WD masses (0.52–1.00 M ) and incorporating different cloud architectures, giant branch stellar mass loss, stellar flybys, Galactic tides and a realistic escape ellipsoid in self-consistent numerical simulations that integrate beyond 8 Gyr ages of WD cooling. We find that ~10 –5 of the material in an exo-Oort cloud is typically amassed on to the WD, and that the H deposits accumulate even as the cloud dissipates. This accumulation may account for the relatively large amount of trace H, 10 22 –10 25  g, that is determined frequently among WDs with cooling ages ≥1 Gyr. Our results also reaffirm the notion that exo-Oort cloud comets are not the primary agents of the metal budgets observed in polluted WD atmospheres.

Description: In this work, we investigate the statistical computation of the Boltzmann entropy of statistical samples. For this purpose, we use both histogram and kernel function to estimate the probability density function of statistical samples. We find that, due to coarse-graining, the entropy is a monotonic increasing function of the bin width for histogram or bandwidth for kernel estimation, which seems to be difficult to select an optimal bin width/bandwidth for computing the entropy. Fortunately, we notice that there exists a minimum of the first derivative of entropy for both histogram and kernel estimation, and this minimum point of the first derivative asymptotically points to the optimal bin width or bandwidth. We have verified these findings by large amounts of numerical experiments. Hence, we suggest that the minimum of the first derivative of entropy be used as a selector for the optimal bin width or bandwidth of density estimation. Moreover, the optimal bandwidth selected by the minimum of the first derivative of entropy is purely data-based, independent of the unknown underlying probability density distribution, which is obviously superior to the existing estimators. Our results are not restricted to one-dimensional, but can also be extended to multivariate cases. It should be emphasized, however, that we do not provide a robust mathematical proof of these findings, and we leave these issues with those who are interested in them.

Description: HD 76431 is a slow rotating post-HB star that shows an underabundance of helium by 0.5 dex relative to the solar value. These observational facts suggest that atomic diffusion could be active in its atmosphere. We have used the MMT and Bok spectra to estimate the atmospheric parameters of the target star using the model atmospheres and synthetic spectra calculated with tlusty and synspec . The derived values of the effective temperature, surface gravity, and helium abundance are consistent with those obtained by Ramspeck et al. It appears that non-local thermodynamic equilibrium (NLTE) effects are not important for HD 76431. We have used Stokes I spectra from ESPaDOnS at CFHT to perform an abundance analysis and a search for observational evidence of vertical stratification of the abundance of certain elements. The results of our abundance analysis are in good agreement with previously published data with respect to average abundances. Our numerical simulations show that carbon and nitrogen reveal signatures of vertical abundance stratification in the atmosphere of HD 76431. It appears that the carbon abundance increases towards the deeper atmospheric layers. Nitrogen also shows a similar behaviour, but in deeper atmospheric layers we obtain a significant dispersion for the estimates of its abundance. To our knowledge, this is the first demonstration of vertical abundance stratification of metals in a post-HB star and up to now it is the hottest star to show such stratification features. We also report the detection of two Si iii and one Ti iii emission lines in the spectra of HD 76431 that were not detected in previous studies.

Description: The Exoplanet Euclid Legacy Survey (ExELS) proposes to determine the frequency of cold exoplanets down to Earth mass from host separations of ~1 au out to the free-floating regime by detecting microlensing events in Galactic bulge. We show that ExELS can also detect large numbers of hot, transiting exoplanets in the same population. The combined microlensing+transit survey would allow the first self-consistent estimate of the relative frequencies of hot and cold sub-stellar companions, reducing biases in comparing ‘near-field’ radial velocity and transiting exoplanets with ‘far-field’ microlensing exoplanets. The age of the bulge and its spread in metallicity further allows ExELS to better constrain both the variation of companion frequency with metallicity and statistically explore the strength of star–planet tides. We conservatively estimate that ExELS will detect ~4100 sub-stellar objects, with sensitivity typically reaching down to Neptune-mass planets. Of these, ~600 will be detectable in both Euclid's VIS (optical) channel and Near Infrared Spectrometer and Photometer (NISP)- H -band imager, with ~90 per cent of detections being hot Jupiters. Likely scenarios predict a range of 2900–7000 for VIS and 400–1600 for H band. Twice as many can be expected in VIS if the cadence can be increased to match the 20-min H -band cadence. The separation of planets from brown dwarfs via Doppler boosting or ellipsoidal variability will be possible in a handful of cases. Radial velocity confirmation should be possible in some cases, using 30 m-class telescopes. We expect secondary eclipses, and reflection and emission from planets to be detectable in up to ~100 systems in both VIS and NISP- H . Transits of ~500 planetary-radius companions will be characterized with two-colour photometry and ~40 with four-colour photometry (VIS, YJH ), and the albedo of (and emission from) a large sample of hot Jupiters in the H band can be explored statistically.

Description: Motivated by the picture of a thin accretion disc around a black hole, radiating mainly in the direction perpendicular to its plane, we study the motion of test particles interacting with a test geodesic radiation flux originating in the equatorial plane of a Schwarzschild space–time and propagating initially in the perpendicular direction. We assume that the interaction with the test particles is modelled by an effective term corresponding to the Thomson-type interaction which governs the Poynting–Robertson effect. After approximating the individual photon trajectories adequately, we solve the continuity equation approximately in order to find a consistent flux density with a certain plausible prescribed equatorial profile. The combined effects of gravity and radiation are illustrated in several typical figures which confirm that the particles are generically strongly influenced by the flux. In particular, they are both collimated and accelerated in the direction perpendicular to the disc, but this acceleration is not enough to explain highly relativistic outflows emanating from some black hole–disc sources. The model can however be improved in a number of ways before posing further questions which are summarized in concluding remarks.

Description: We report the detection of Ne viii in a z abs = 0.599 61 absorber towards the QSO PG1407+265 ( z em = 0.94). Besides Ne viii , absorption from H i Lyman series lines (H i  1025–915), several other low (C ii , N ii , O ii and S ii ), intermediate (C iii , N iii , N iv , O iii , S iv and S v ) and high (S vi , O vi and Ne viii ) ionization metal lines are detected. Disparity in the absorption line kinematics between different ions implies that the absorbing gas comprises of multiple ionization phases. The low and the intermediate ions (except S v ) trace a compact (~410 pc), metal-rich ( Z  ~ Z ) and overdense (log n H  ~ –2.6) photoionized region that sustained star formation for a prolonged period. The high ions, Ne viii and O vi , can be explained as arising in a low density (–5.3 ≤ log n H ≤ –5.0), metal-rich ( Z Z ) and diffuse (~180 kpc) photoionized gas. The S v , S vi and C iv [detected in the Faint Object Spectrograph (FOS) spectrum] require an intermediate photoionization phase with –4.2 〈 log n H  〈 –3.5. Alternatively, a pure collisional ionization model, as used to explain the previous known Ne viii absorbers, with 5.65 〈 log T  〈 5.72, can reproduce the S vi , O vi and Ne viii column densities simultaneously in a single phase. However, even such models require an intermediate phase to reproduce any observable S v and/or C iv . Therefore, we conclude that when multiple phases are present, the presence of Ne viii is not necessarily an unambiguous indication of collisionally ionized hot gas.

Description: Depopulation of metastable He(2 3 S) and He(2 1 S) by radiative association with helium ions resulting in the formation of the He $_{2}^{+}$ molecular ions is investigated. Rate coefficients for spontaneous radiative association of the He $_{2}^{+}$ molecular ion on the spin-doublet manifold are presented as functions of temperature from 10 up to 500 000 K considering the association to rotational-vibrational bound states of the lowest doublet electronic states $X^{2}\Sigma ^{+}_{u}$ and $A^{2}\Sigma ^{+}_{g}$ from the continuum states of the excited doublet electronic states $B^{2}\Sigma ^{+}_{u}$ and $D^{2}\Sigma ^{+}_{u}$ . The dipole-driven processes B -〉 A and D -〉 A are compared to the quadrupole-driven processes B -〉 X and D -〉 X . For all considered temperatures, the dipole-driven process D -〉 A dominates over the other processes. The rate coefficient for the quadrupole-driven process B -〉 X is at least three orders of magnitude larger than the rate coefficient of the dipole-driven process B -〉 A .

Description: We present the results of a new analysis of the X-ray selected active galactic nuclei (AGN) population residing in and behind 135 of the most massive galaxy clusters in the redshift range of 0.2 〈  z  〈 0.9 observed with Chandra . With a sample of more than 11 000 X-ray point sources, we are able to measure, for the first time, evidence for evolution in the cluster AGN population beyond the expected evolution of field AGN. Our analysis shows that overall number density of cluster AGN scales with the cluster mass as ~ M 500 – 1.2 . There is no evidence for the overall number density of cluster member X-ray AGN depending on the cluster redshift in a manner different than field AGN, nor is there any evidence that the spatial distribution of cluster AGN (given in units of the cluster overdensity radius r 500 ) strongly depends on the cluster mass or redshift. The M –1.2 ± 0.7 scaling relation we measure is consistent with theoretical predictions of the galaxy merger rate in clusters, which is expected to scale with the cluster velocity dispersion, , as ~ –3 or ~ M –1 . This consistency suggests that galaxy mergers may be an important contributor to the cluster AGN population, a result that is further corroborated by visual inspection of Hubble images for 23 spectroscopically confirmed cluster member AGN in our sample. A merger-driven scenario for the triggering of X-ray AGN is not strongly favoured by studies of field galaxies, however, suggesting that different mechanisms may be primarily responsible for the triggering of cluster and field X-ray AGN.

Description: The analysis of SOlar and Heliospheric Observatory ( SOHO ) Solar Wind ANisotropies (SWAN) data for backscattered solar Lyman α radiation performed by Lallement et al. showed for the first time that the average direction of interstellar hydrogen flow in the heliosphere is deflected by several degrees relative to the original direction of the interstellar wind outside the heliosphere. This deflection is caused by the indirect influence of the interstellar magnetic field (IsMF) through charge exchange between hydrogen atoms and interstellar protons deflected by the IsMF in the region of interaction between the solar wind and the local interstellar medium (LISM). Thus, measurements of the backscattered Lyman α radiation at the Earth's orbit can be used as a remote IsMF diagnostic. However, the direction of interstellar hydrogen flow in the vicinity of the Sun may be influenced by other effects such as the solar radiation pressure, gravitation and ionization and kinetic non-Maxwellian properties of the hydrogen distribution and also may depend on other LISM parameters besides IsMF. In this work, we perform a theoretical modelling of the backscattered solar Lyman α radiation seen at 1 au from the Sun and analyse the direction of hydrogen flow in the heliosphere, which can be obtained from the spectral properties of the backscattered radiation. The influence of different effects mentioned above is investigated. Also we compare our results obtained by means of a state-of-art 3D time-dependent kinetic model of the hydrogen distribution with the SWAN data of 1996.

Description: Type Ia supernovae (SNe Ia) are often used as the standard candles to probe the anisotropic expansion of the Universe. In this paper, we make a comprehensive comparison between the hemisphere comparison (HC) method and dipole-fitting (DF) method in searching for the cosmological preferred direction using the Union2 data set, a compilation of 557 well-calibrated SNe Ia. We find that the directions of the faintest SNe Ia derived from these two methods are approximately opposite. Monte Carlo simulations show that the results of the HC method strongly depend on the distribution of the data points in the sky. The coincidence that the HC method and DF method give two completely opposite directions may be due to the extremely non-uniform distribution of the Union2 data set.

Description: We show that if young low-mass stars are subject to vigorous X-ray driven disc winds, then such winds may be rendered detectable in cluster environments through their interaction with ionizing radiation from massive stars. In particular we argue that in the Orion nebula cluster (ONC) one expects to see of order tens of ‘X-ray proplyds’ (i.e. objects with offset ionization fronts detectable through optical imaging) in the range 0.3–0.6 pc from 1 C Ori (the dominant O star in the ONC). Objects at this distance lie outside the central ‘FUV zone’ in the ONC where proplyd structures are instead well explained by neutral winds driven by external far-ultraviolet (FUV) emission from 1 C Ori. We show that the predicted numbers and sizes of X-ray proplyds in this region are compatible with the numbers of proplyds observed and that this may also provide an explanation for at least some of the far flung proplyds observed in the Carina nebula. We compare the sizes of observed proplyds outside the FUV region of the ONC with model predictions based on the current observed X-ray luminosities of these sources (bearing in mind that the current size is actually set by the X-ray luminosity a few hundred years previously, corresponding to the flow time to the ionization front). We discuss whether variability on this time-scale can plausibly explain the proplyd size data on a case-by-case basis. We also calculate the predicted radio free–free emission signature of X-ray proplyds and show that this is readily detectable. Monitoring is, however, required in order to distinguish such emission from non-thermal radio emission from active coronae. We also predict that it is only at distances more than a parsec from 1 C Ori that the free–free emission signature of such offset ionized structures would be clearly distinguishable from an externally driven ionized disc wind. We argue that the fortuitous proximity of massive stars in the ONC can be used as a beacon to light up internally driven X-ray winds and that this represents a promising avenue for observational tests of the X-ray photoevaporation scenario.

Description: Cross-correlating the Planck High Frequency Instrument maps against quasars from the Sloan Digital Sky Survey DR7, we estimate the intensity distribution of the cosmic infrared background (CIB) over the redshift range 0 〈  z  〈 5. We detect redshift-dependent spatial cross-correlations between the two data sets using the 857, 545, and 353 GHz channels and we obtain upper limits at 217 GHz consistent with expectations. At all frequencies with detectable signal we infer a redshift distribution peaking around z  ~ 1.2 and find the recovered spectrum to be consistent with emission arising from star-forming galaxies. By assuming simple modified blackbody and Kennicutt relations, we estimate dust and star formation rate density as a function of redshift, finding results consistent with earlier multiwavelength measurements over a large portion of cosmic history. However, we note that, lacking mid-infrared coverage, we are not able to make an accurate determination of the mean temperature for the dust responsible for the CIB. Our results demonstrate that clustering-based redshift inference is a valuable tool for measuring the entire evolution history of the cosmic star formation rate from a single and homogeneous data set.

Description: While wide-field surveys of M31 have revealed much substructure at large radii, understanding the nature and origin of this material is not straightforward from morphology alone. Using deep Hubble Space Telescope /Advanced Camera for Surveys data, we have derived further constraints in the form of quantitative star formation histories (SFHs) for 14 inner halo fields which sample diverse substructures. In agreement with our previous analysis of colour–magnitude diagram morphologies, we find the resultant behaviours can be broadly separated into two categories. The SFHs of ‘disc-like’ fields indicate that most of their mass has formed since z  ~ 1, with one quarter of the mass formed in the last 5 Gyr. We find ‘stream-like’ fields to be on average 1.5 Gyr older, with 10 per cent of their stellar mass formed within the last 5 Gyr. These fields are also characterized by an age–metallicity relation showing rapid chemical enrichment to solar metallicity by z  = 1, suggestive of an early-type progenitor. We confirm a significant burst of star formation 2 Gyr ago, discovered in our previous work, in all the fields studied here. The presence of these young stars in our most remote fields suggests that they have not formed in situ but have been kicked-out from the thin disc through disc heating in the recent past.

Description: The solar analogues 16 Cyg A and B are excellent asteroseismic targets in the Kepler field of view and together with a red dwarf and a Jovian planet form an interesting system. For these more evolved Sun-like stars we cannot detect surface rotation with the current Kepler data but instead use the technique of asteroseimology to determine rotational properties of both 16 Cyg A and B. We find the rotation periods to be $23.8^{+1.5}_{-1.8}$ and $23.2^{+11.5}_{-3.2} \rm \, d$ , and the angles of inclination to be $56^{+6}_{-5} \, ^{\circ }$ and $36^{+17}_{-7} \, ^{\circ }$ , for A and B, respectively. Together with these results we use the published mass and age to suggest that, under the assumption of a solar-like rotation profile, 16 Cyg A could be used when calibrating gyrochronology relations. In addition, we discuss the known 16 Cyg B star–planet eccentricity and measured low obliquity which is consistent with Kozai cycling and tidal theory.

Description: Current wide-area radio surveys are dominated by active galactic nuclei, yet many of these sources have no identified optical counterparts. Here we investigate whether one can constrain the nature and properties of these sources, using Fanaroff–Riley type II (FR II) radio galaxies as probes. These sources are easy to identify since the angular separation of their lobes remains almost constant at some tens of arcseconds for z  〉 1. Using a simple algorithm applied to the Faint Images of the Radio Sky at Twenty-cm survey, we obtain the largest FR II sample to date, containing over 10 4 double-lobed sources. A subset of 459 sources is matched to Sloan Digital Sky Survey quasars. This sample yields a statistically meaningful description of the fraction of quasars with lobes as a function of redshift and luminosity. This relation is combined with the bolometric quasar luminosity function and a disc–lobe correlation to obtain a robust prediction for the density of FR IIs on the radio sky. We find that the observed density can be explained by the population of known quasars, implying that the majority of powerful jets originate from a radiatively efficient accretion flow with a linear jet–disc coupling. Finally, we show that high-redshift jets are more often quenched within 100 kpc, suggesting a higher efficiency of jet-induced feedback into their host galaxies.

Description: The extremely high-redshift ( z  = 5.3) radio source SDSS J102623.61+254259.5 (J1026+2542) is among the most distant and most luminous radio-loud active galactic nuclei (AGN) known to date. Its one-sided radio jet structure on milliarcsecond (mas) and ~10-mas scales typical for blazars was first imaged at 5 GHz with very long baseline interferometry (VLBI) in 2006. Here we report on our dual-frequency (1.7 and 5 GHz) imaging observations performed with the European VLBI Network (EVN) in 2013. The prominent jet structure allows us to identify individual components whose apparent displacement can be detected over the time span of 7.33 yr. This is the first time when jet proper motions are directly derived in a blazar at z  〉 5. The small values of up to ~0.1 mas yr –1 are consistent with what is expected in a relativistic cosmological model if redshift is a measure of distance. The apparent superluminal jet speeds, considered tentative because derived from two epochs only, exceed 10  c for three different components along the jet. Based on modelling its spectral energy distribution, J1026+2542 is known to have its X-ray jet oriented close to the line of sight, with significant Doppler boosting and a large bulk Lorentz factor (  13). The new VLBI observations, indicating ~2.3 10 12  K lower limit to the core brightness temperature, are consistent with this picture. The spectral index in the core region is –0.35.

Description: We consider the evolution of metal-enriched gas exposed to a superposition of the time-dependent radiation field of a nearby starburst galaxy and a nearly invariant (on time-scales of 100 Myr) extragalactic ionization background. Using non-equilibrium (time-dependent) photoionization models, we determine the ionization fraction of the O  vi ion commonly observed in the galactic circumference. We then derive the conditions for O  vi to appear in absorption in extended galactic haloes, depending on the galactic mass and star formation rate. We have found that the maximum O  vi fraction can reach ~0.4–0.9 under the combined action of galactic and extragalactic ionizing radiation fields. We conclude that soft X-ray emission with E   113 eV from the stellar population of central star-forming galaxies is the main source of such a high fraction of O  vi . This circumstance can explain the high column densities, ${N(\rm O\,\small {vi})} \sim 10^{14.5\mbox{--}15.3}$  cm –2 , observed in the haloes of star-forming galaxies at low redshifts even for relatively low (~0.01–0.1 Z ) metallicity. As a result, the requirements for sources of oxygen in extended haloes relax to a reasonably conservative level. We show that, at z   0.5, the ionization kinetics of oxygen in a relatively dense plasma, n   10 –4  cm –3 , of an outer halo exposed to a low extragalactic ionizing flux is dominated by non-equilibrium effects.

Description: The VISTA (Visible and Infrared Survey Telescope for Astronomy) survey of the Magellanic Clouds System (VMC) is collecting deep K s -band time-series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper, we have analysed a sample of 130 Large Magellanic Cloud (LMC) Type II Cepheids (T2CEPs) found in tiles with complete or near-complete VMC observations for which identification and optical magnitudes were obtained from the OGLE III (Optical Gravitational Lensing Experiment) survey. We present J and K s light curves for all 130 pulsators, including 41 BL Her, 62 W Vir (12 pW Vir) and 27 RV Tau variables. We complement our near-infrared photometry with the V magnitudes from the OGLE III survey, allowing us to build a variety of period–luminosity (PL), period–luminosity–colour (PLC) and period–Wesenheit (PW) relationships, including any combination of the V , J , K s filters and valid for BL Her and W Vir classes. These relationships were calibrated in terms of the LMC distance modulus, while an independent absolute calibration of the PL( K s ) and the PW( K s , V ) was derived on the basis of distances obtained from Hubble Space Telescope parallaxes and Baade–Wesselink technique. When applied to the LMC and to the Galactic globular clusters hosting T2CEPs, these relations seem to show that (1) the two Population II standard candles RR Lyrae and T2CEPs give results in excellent agreement with each other; (2) there is a discrepancy of ~0.1 mag between Population II standard candles and classical Cepheids when the distances are gauged in a similar way for all the quoted pulsators. However, given the uncertainties, this discrepancy is within the formal 1 uncertainties.

Description: Building on the results of a previous paper, we compute for the first time a full first-order perturbative solution for the angular coordinates in the restricted post-Newtonian two-body problem with spin. The analytical integration of the angular coordinates, based on the theory of the Weierstrassian functions, allows us to investigate thoroughly the spin–orbit and spin–spin interactions, and to derive several new results. The application of our solution to a selection of idealized physical systems of interest reveals a rich variety of dynamical behaviours driven by purely relativistic effects. In particular, we highlight a new relativistic nutational motion resulting from the combined spin–orbit and spin–spin interactions.

Description: In this paper we aim to (i) test the number of statistically distinct classes required to classify the local galaxy population and (ii) identify the differences in the physical and star formation properties of visually distinct galaxies. To accomplish this, we analyse the structural parameters – effective radius ( R eff ), effective surface brightness within R eff (〈μ〉 e ), central surface brightness (μ 0 ) and Sérsic index ( n ) – obtained by fitting the light profile of 432 galaxies (0.002 〈  z  ≤ 0.02; Viking Z band), and their spectral energy distribution using multiband photometry in 18 broad-bands to obtain the stellar mass ( M *), the star formation rate (SFR), the specific SFR (sSFR) and the dust mass ( M dust ), respectively. We show that visually distinct, star-forming dwarf galaxies (irregulars, blue spheroids and low-surface-brightness galaxies) form a unimodal population in a parameter space mapped by 〈μ〉 e , μ 0 , n , R eff , SFR, sSFR, M *, M dust and ( g – i ). The SFR and sSFR distribution of passively evolving (dwarf) ellipticals on the other hand, statistically distinguish them from other galaxies with similar luminosity, while the giant galaxies clearly segregate into star-forming spirals and passive lenticulars. We therefore suggest that the morphology classification scheme(s) used in literature for dwarf galaxies only reflect the observational differences based on luminosity and surface brightness among the apparent distinct classes, rather than any physical differences between them.

Description: In this paper, we give a detailed account of the first three-dimensional (3D) relativistic magnetohydrodynamic simulations of pulsar wind nebulae, with parameters most suitable for the Crab nebula. In contrast to the previous 2D simulations, we also consider pulsar winds with much stronger magnetization, up to  ~= few. The 3D models preserve the separation of the post-termination shock flow into the equatorial and polar components, but the polar jets are disrupted by the kink mode of the current driven instability and ‘dissolve’ into the main body of the nebula after propagation of several shock radii. With the exception of the region near the termination shock, the 3D models do not exhibit the strong z -pinch configuration characteristic of the 1D and 2D models. Contrary to the expectations based on 1D analytical and semi-analytical models, the 3D solutions with highly magnetized pulsar winds still produce termination shocks with radii comparable to those deduced from the observations. The reason for this is not only the randomization of magnetic field observed in the 3D solutions, but also the magnetic dissipation inside the nebula. Assuming that the particle acceleration occurs only at the termination shock, we produced synthetic maps of the Crab nebula synchrotron emission. These maps retain most of the features revealed in the previous 2D simulations, including thin wisps and the inner knot. The polarization and variability of the inner knot is in a particularly good agreement with the observations of the Crab nebula and the overall polarization of the inner nebula is also reproduced quite well. However, the polar jet is not as bright as observed, suggesting that an additional particle acceleration, presumably related to the magnetic dissipation, has to be invoked.

Description: We investigate the accretion rate, bolometric luminosity, black hole (BH) growth time and BH spin in a large active galactic nucleus (AGN) sample under the assumption that all such objects are powered via thin or slim accretion discs (ADs). We use direct estimates of the mass accretion rate, $\dot{M}$ , to show that many currently used values of L bol and L / L Edd are either underestimated or overestimated because they are based on bolometric correction factors that are adjusted to the properties of moderately accreting AGNs and do not take into account the correct combination of BH mass, spin and accretion rate. The consistent application of AD physics to our sample of Sloan Digital Sky Survey (SDSS) AGNs leads to the following findings. (1) Even the most conservative assumption about the radiative efficiency of fast-accreting BHs shows that many of these sources must contain slim ADs. We illustrate this by estimating the fraction of such objects at various redshifts. (2) Many previously estimated BH growth times are inconsistent with the AD theory. In particular, the growth times of the fastest accreting BHs were overestimated in the past by large factors with important consequences to AGN evolution. (3) Currently used bolometric correction factors for low accretion rate very massive SDSS BHs are inconsistent with the AD theory. Applying the AD set of assumptions to such objects, combined with standard photoionization calculations of broad emission lines, leads to the conclusion that many such objects must contain fast-spinning BHs.

Description: This paper describes an explicit multidimensional numerical scheme for special relativistic two-fluid magnetohydrodynamics of electron–positron plasma and a suit of test problems. The scheme utilizes Cartesian grid and the third-order weighted essentially non-oscillatory interpolation. Time integration is carried out using the third-order total variation diminishing method of Runge–Kutta type, thus ensuring overall third-order accuracy on smooth solutions. The magnetic field is kept near divergence-free by means of the method of generalized Lagrange multiplier. The test simulations, which include linear and non-linear continuous plasma waves, shock waves, strong explosions and the tearing instability, show that the scheme is sufficiently robust and confirm its accuracy.

Description: We measure the angular clustering of 33 415 extremely red objects (EROs) in the Elais-N1 field covering 5.33 deg 2 , which cover the redshift range z  = 0.8 to 2. This sample was made by merging the UKIDSS Deep eXtragalactic Survey (DXS) with the optical Subaru and Pan-STARRS PS1 data sets. We confirm the existence of a clear break in the angular correlation function at ~0.02° corresponding to 1 h –1 Mpc at z ~ 1. We find that redder or brighter EROs are more clustered than bluer or fainter ones. Halo occupation distribution (HOD) model fits imply that the average mass of dark matter haloes which host EROs is over 10 13 h –1 M and that EROs have a bias ranging from 2.7 to 3.5. Compared to EROs at z ~ 1.1, at z ~ 1.5 EROs have a higher bias and fewer are expected to be satellite galaxies. Furthermore, EROs reside in similar dark matter haloes to those that host 10 11.0 M  〈  M *  〈 10 11.5 M galaxies. We compare our new measurement and HOD fits with the predictions of the galform semi-analytical galaxy formation model. Overall, the clustering predicted by galform gives an encouraging match to our results. However, compared to our deductions from the measurements, galform puts EROs into lower mass haloes and predicts that a larger fraction of EROs are satellite galaxies. This suggests that the treatment of gas cooling may need to be revised in the model. Our analysis illustrates the potential of clustering analyses to provide observational constraints on theoretical models of galaxy formation.

Description: Symbiotic stars are long-orbital-period interacting binaries characterized by extended emission over the whole electromagnetic range and by complex photometric and spectroscopic variability. In this paper, the first of a series, we present Optical Gravitational Lensing Experiment (OGLE) light curves of all the confirmed symbiotic stars in the Large Magellanic Cloud, with one exception. By careful visual inspection and combined time series analysis techniques, we investigate for the first time in a systematic way the photometric properties of these astrophysical objects, trying in particular to distinguish the nature of the cool component (e.g. semiregular Variable versus OGLE small-amplitude red giant), to provide its first-order pulsational ephemerides and to link all this information with the physical parameters of the binary system as a whole. Among the most interesting results, there is the discovery of a 20 yr-long steady fading of Sanduleak's star, a peculiar symbiotic star known to produce the largest stellar jet ever discovered. We discuss by means of direct examples the crucial need for long-term multi-band observations to get a real understanding of symbiotic and other interacting binary stars. We eventually introduce BOMBOLO, a multi-band simultaneous imager for the Southern Astrophysical Research 4 m Telescope, whose design and construction we are currently leading.

Description: We examine systematic differences in the derived X-ray properties of galaxy clusters as reported by three different groups: Vikhlinin et al., Mantz et al. and Plank Collaboration. The sample overlap between any two pairs of works ranges between 16 to 28 galaxy clusters. We find systematic differences in most reported X-ray properties, including the total cluster mass, M 500 . The most extreme case is an average 45 ± 5 per cent difference in cluster mass between the Plank Collaboration and Mantz et al., for clusters at z  〉 0.13 (averaged over 16 clusters). These differences also induce differences in cluster observables defined within an R 500 aperture. After accounting for aperture differences, we find very good agreement in gas mass estimates between the different groups. However, the soft-band X-ray luminosity, L X , core-excised spectroscopic temperature, T X , and gas thermal energy, Y X  =  M gas T X display mean differences at the 5–15 per cent level. We also find that the low ( z ≤ 0.13) and high ( z  ≥ 0.13) redshift galaxy cluster samples in Plank Collaboration appear to be systematically different: the Y SZ / Y X ratio for each of these two sub-samples is ln ( Y SZ / Y X ) = –0.06 ± 0.04 and ln ( Y SZ / Y X ) = 0.08 ± 0.04, respectively.

Description: Transient surveys have recently discovered a class of supernovae (SNe) with extremely rapidly declining light curves. These events are also often relatively faint, especially compared to Type Ia SNe. The common explanation for these events involves a weak explosion, producing a radioactive outflow with small ejected mass and kinetic energy ( M  ~ 0.1 M and E  ~ 0.1 B, respectively), perhaps from the detonation of a helium shell on a white dwarf. We argue, in contrast, that these events may be Type Ib/c SNe with typical masses and energies ( M  ~ 3 M , E  ~ 1 B), but which ejected very little radioactive material. In our picture, the light curve is powered by the diffusion of thermal energy deposited by the explosion shock wave, and the rapid evolution is due to recombination, which reduces the opacity and results in an ‘oxygen-plateau’ light curve. Using a radiative transfer code and simple 1D ejecta profiles, we generate synthetic spectra and light curves and demonstrate that this model can reasonably fit the observations of one event, SN 2010X. Similar models may explain the features of other rapidly evolving SNe such as SN 2002bj and SN 2005ek. SNe such as these may require stripped-envelope progenitors with rather large radii ( R  ~ 20 R ), which may originate from a mass-loss episode occurring just prior to explosion.

Description: This is the first paper in a dedicated series to study the properties of the optically-selected broad-line-region-less (BLR-less) active galactic nuclei (AGNs; with no-hidden central broad emission line regions). We carried out a systematic search for the BLR-less AGNs through the Sloan Digital Sky Survey Legacy Survey (SDSS Stripe82 Database). Based on the spectral decomposition results for all the 136 676 spectroscopic objects (galaxies and quasars) with redshift less than 0.35 covered by the SDSS Stripe82 region, our spectroscopic sample for the BLR-less AGNs includes 22 693 pure narrow line objects without broad emission lines but with apparent AGN continuum emission R AGN  〉 0.3 and apparent stellar lights R ssp  〉 0.3. Then, using the properties of the photometry magnitude RMS ( RMS ) and Pearson's coefficients ( R 1, 2 ) between two different SDSS band light curves: $RMS_k 〉 3\times RMS_{M_k}$ and R 1, 2  〉 ~0.8, the final 281 pure narrow line objects with true photometry variabilities are our selected reliable candidates for the BLR-less AGNs. The selected candidates with higher confidence levels not only have the expected spectral features of the BLR-less AGNs, but also show significant true photometry variabilities. The reported sample enlarges at least four times the current sample of the BLR-less AGNs, and will provide more reliable information to explain the lack of the BLRs of AGNs in our following studies.

Description: We evaluate a distribution function for the system of galaxies clustering gravitationally in an expanding universe on the basis of statistical mechanics. We extend our previous work to incorporate the effect of any ratio of gravitational potential to kinetic energies. We determine the cosmological many-body partition function inclusive of higher order terms and calculate all thermodynamic quantities and the distribution function from it. We find that our new results are consistent with the previous ones, particularly in the large $\bar{N}$ (average number of galaxies) limit. We also investigate the effect on clustering parameter b and find our new results in very good agreement with the previous ones in the small b limit. We find that for large b , the departure from the original distribution function is greater. We also observe that the effect of softening on the distribution function is consistent with our previous work.

Description: We estimate the turbulent ambipolar diffusion length-scale and magnetic field strength in the massive dense cores CygX-N03 and CygX-N53, located in the Cygnus-X star-forming region. The method we use requires comparing the velocity dispersions in the spectral line profiles of the coexistent ion and neutral pair H 13 CN and H 13 CO + ( J  = 1 -〉 0) at different length-scales. We fit Kolmogorov-type power laws to the lower envelopes of the velocity dispersion spectra of the two species. This allows us to calculate the turbulent ambipolar diffusion scale, which in turn determines the plane-of-the-sky magnetic field strength. We find turbulent ambipolar diffusion length-scales of 3.8 ± 0.1 and 21.2 ± 0.4 mpc, and magnetic field strengths of 0.33 and 0.76 mG for CygX-N03 and CygX-N53, respectively. These magnetic field values have uncertainties of a factor of a few. Despite a lower signal-to-noise ratio of the data in CygX-N53 than in CygX-N03, and the caveat that its stronger field might stem in part from projection effects, the difference in field strengths suggests different fragmentation efficiencies of the two cores. Even though the quality of our data, obtained with the Institut de Radio Astronomie Millimetrique (IRAM) Plateau de Bure Interferometer, is somewhat inferior to previous single-dish data, we demonstrate that this method is suited also for observations at high spatial resolution.

Description: The dramatic relativistic jets pointing directly at us in BL Lacertae (BL Lac) objects can be well modelled by bulk motion beaming of synchrotron self-Compton emission powered by a low Eddington fraction accretion flow. Nearly 500 of these active galactic nuclei (AGN) are seen in the second Fermi Large Area Telescope catalogue of AGN. We combine the jet models which describe individual spectra with the expected jet parameter scalings with mass and mass accretion rate to predict the expected number of Fermi detected sources given the number densities of AGN from cosmological simulations. We select only sources with Eddington scaled mass accretion rate 〈0.01 (i.e. radiatively inefficient flows), and include cooling, orientation effects and the effects of absorption from pair production on the extragalactic infrared background. These models overpredict the number of Fermi detected BL Lacs by a factor of 1000! This clearly shows that one of the underlying assumptions is incorrect, almost certainly that jets do not scale simply with mass and accretion rate. The most plausible additional parameter which can affect the region producing the Fermi emission is black hole spin. We can reproduce the observed numbers of BL Lacs if such relativistic jets are only produced by the highest spin ( a *  〉 0.8) black holes, in agreement with the longstanding spin–jet paradigm. This also requires that high spins are intrinsically rare, as predicted by the cosmological simulations for growing black hole mass via chaotic (randomly aligned) accretion episodes, where only the most massive black holes have high spin due to black hole–black hole mergers.

Description: Stark widths and shifts of Cr ii lines with wavelengths in the range 2000–3500 Å have been determined by laser-induced breakdown spectroscopy. The spectra have been measured at different instants of the plasma evolution from 0.6 to 3.4 μs, at which the temperature and electron density are in the ranges 12 000–16 300 K and (0.89–8.2) 10 17 cm –3 , respectively. The laser-induced plasmas have been generated from three fused glass samples with different chromium concentrations, selected to control the self-absorption of the lines. The Stark widths and shifts are compared with the experimental and theoretical data available in the literature.

Description: We present near-infrared ( H - and K -band) integral-field observations of the inner ~700 pc of the active spiral galaxy NGC 613, obtained with SINFONI on the Very Large Telescope. We use emission-line ratios to determine the dominant excitation mechanisms in different regions within our field of view, in particular, the active nucleus and the star-forming circumnuclear ring. Diagnostic diagrams involving [Fe ii ] and H 2 fluxes indicate that the gas is not only photoionized by the active galactic nucleus (AGN) in the nucleus of NGC 613, but also shock heated. On the other hand, the emission-line ratios measured in the ‘hotspots’ along the ring are fully consistent with them being young star-forming regions. We find no sign of radial gas transport from the ring into the core region dominated by the AGN. The ring morphology appears disturbed by a radial outflow of material from the AGN, which is confirmed by the existence of a weak jet in archival radio maps. However, this jet does not seem to have any significant effect on the morphology of the large (~8 10 7 M ) reservoir of molecular gas that has accumulated inside the central ~100 pc. Such a concentration of molecular gas around an AGN is unusual, and supports a scenario in which star formation is recurrent and episodic in spiral galaxies. In this context, NGC 613 appears to be in final stages of the gas accumulation phase and is likely to undergo a nuclear starburst in the near future.

Description: The interaction of differential rotation and toroidal fields that are current-free in the gap between two corotating axially unbounded cylinders is considered. It is shown that non-axisymmetric perturbations are unstable if the rotation rate and Alfvén frequency of the field are of the same order, almost independent of the magnetic Prandtl number Pm. For the very steep rotation law    R –2 (the Rayleigh limit) and for small Pm, the threshold values of rotation and field for this azimuthal magnetorotational instability (AMRI) scale with the ordinary Reynolds number and the Hartmann number, respectively. A laboratory experiment with liquid metals like sodium or gallium in a Taylor–Couette container has been designed on the basis of this finding. For fluids with more flat rotation laws, the Reynolds number and the Hartmann number are no longer typical quantities for the instability. For the weakly non-linear system, the numerical values of the kinetic energy and the magnetic energy are derived for magnetic Prandtl numbers ≤ 1. We find that the magnetic energy grows monotonically with the magnetic Reynolds number Rm, while the kinetic energy grows with ${\rm Rm}/\sqrt{\rm Pm}$ . The resulting turbulent Schmidt number, as the ratio of the ‘eddy’ viscosity and the diffusion coefficient of a passive scalar (such as lithium), is of the order of 20 for Pm = 1, but for small Pm it drops to the order of unity. Hence, in a stellar core with fossil fields and steep rotation law, the transport of angular momentum by AMRI is always accompanied by an intense mixing of the plasma, until the rotation becomes rigid.

Description: We analyse line-of-sight velocity and proper motion data of stars in the Galactic globular cluster M15 using a new method to fit dynamical models to discrete kinematic data. Our fitting method maximizes the likelihood for individual stars and, as such, does not suffer the same loss of spatial and velocity information incurred when spatially binning data or measuring velocity moments. In this paper, we show that the radial variation in M15 of the mass-to-light ratio is consistent with previous estimates and theoretical predictions, which verifies our method. Our best-fitting axisymmetric Jeans models do include a central dark mass of ~2 ± 1 10 3 M , which can be explained by a high concentration of stellar remnants at the cluster centre. This paper shows that, from a technical point of view and with current computing power, spatial binning of data is no longer necessary. This not only leads to more accurate fits, but also avoids biased mass estimates due to the loss of resolution. Furthermore, we find that the mass concentration in M15 is significantly higher than previously measured, and is in close agreement with theoretical predictions for core-collapsed globular clusters without a central intermediate-mass black hole.

Description: We examine recent measurements of the z 2.5 intergalactic medium (IGM) which constrain the H  i frequency distribution $f(N_{\rm H\,{\small I}})$ and the mean free path $\lambda _{\rm mfp}^{912}$ to ionizing radiation. We argue that line-blending and the clustering of strong absorption-line systems have led previous authors to systematically overestimate the effective Lyman limit opacity, yielding too small of a $\lambda _{\rm mfp}^{912}$ for the IGM. We further show that recently published measurements of $f(N_{\rm H\,{\small I}})$ at $N_{\rm H\,{\small I}}\approx 10^{16} \, {\rm cm^{-2}}$ lie in strong disagreement, implying underestimated uncertainty from sample variance and/or systematics like line-saturation. Allowing for a larger uncertainty in the $f(N_{\rm H\,{\small I}})$ measurements, we provide a new cubic Hermite spline model for $f(N_{\rm H\,{\small I}})$ which reasonably satisfies all of the observational constraints under the assumption of randomly distributed absorption systems. We caution, however, that this formalism is invalid in the light of absorber clustering and use a toy model to estimate the effects. Future work must properly account for the non-Poissonian nature of the IGM.

Description: We present ultraviolet, optical, near-infrared photometry and spectroscopy of SN 2009N in NGC 4487. This object is a Type II-P supernova with spectra resembling those of subluminous II-P supernovae, while its bolometric luminosity is similar to that of the intermediate-luminosity SN 2008in. We created synow models of the plateau phase spectra for line identification and to measure the expansion velocity. In the near-infrared spectra we find signs indicating possible weak interaction between the supernova ejecta and the pre-existing circumstellar material. These signs are also present in the previously unpublished near-infrared spectra of SN 2008in. The distance to SN 2009N is determined via the expanding photosphere method and the standard candle method as D  = 21.6 ± 1.1 Mpc. The produced nickel-mass is estimated to be ~0.020 ± 0.004 M . We infer the physical properties of the progenitor at the explosion through hydrodynamical modelling of the observables. We find the values of the total energy as ~0.48 10 51  erg, the ejected mass as ~11.5 M , and the initial radius as ~287 R .

Description: Active galactic nuclei (AGN) are characterized by similar broad emission lines properties at all luminosities (10 39 – 10 47 erg s –1 ). What produces this similarity over a vast range of 10 8 in luminosity? Photoionization is inevitably associated with momentum transfer to the photoionized gas. Yet, most of the photoionized gas in the broad-line region (BLR) follows Keplerian orbits, which suggests that the BLR originates from gas with a large enough column for gravity to dominate. The photoionized surface layer of the gas must develop a pressure gradient due to the incident radiation force. We present solutions for the structure of such a hydrostatic photoionized gas layer in the BLR. The gas is stratified, with a low-density highly ionized surface layer, a density rise inwards and a uniform-density cooler inner region, where the gas pressure reaches the incident radiation pressure. This radiation pressure confinement (RPC) of the photoionized layer leads to a universal ionization parameter U  ~ 0.1 in the inner photoionized layer, independent of luminosity and distance. Thus, RPC appears to explain the universality of the BLR properties in AGN. We present predictions for the BLR emission per unit covering factor, as a function of distance from the ionizing source, for a range of ionizing continuum slopes and gas metallicity. The predicted mean strength of most lines (excluding H β), and their different average-emission radii, are consistent with available observations.

Description: The properties of isolated galaxies are driven mainly by intrinsic evolution and not by the external influence of their environments. Therefore, the sample of isolated galaxies can be considered as a reference sample to study different environmental effects. We have made detailed comparisons between the near-infrared (Two-Micron All-Sky Survey, 2MASS) and optical (Sloan Digital Sky Survey, SDSS) colours of the 2MASS Isolated Galaxies (2MIG) sample selected from the 2MASS Extended Source Catalogue and with other objects from the wide range of denser environments (field, groups/clusters, triplets and pairs). We have found that early-type galaxies show similar ( J  – H ) rest and ( g  – r ) rest colours in practically all types of environments, except for the massive early-type galaxies located in compact pairs with high velocity difference ( dV  ~ 180 km s –1 ), which are significantly redder and brighter than isolated galaxies. We assume that these pairs are located in the centres of more populated groups and clusters. In general, galaxies in groups and pairs of spiral and late morphological types have redder near-infrared colours ( J  – H ) rest than 2MIG isolated galaxies. The ( g  – r ) rest colours of galaxies in groups and pairs with high velocity difference are also significantly redder than the corresponding colours of 2MIG isolated galaxies. In contrast, the members of most compact pairs ( dV  ~ 50 km s –1 , R  ~ 30 kpc) show the same ( g  – r ) rest colour and even tend to be bluer than 2MIG isolated galaxies. In summary, our results show that the colours of galaxies depend very much on external factors.

Description: We explore the role of environment in the evolution of galaxies over 0.1 〈 z  〈 0.7 using the final zCOSMOS-bright data set. Using the red fraction of galaxies as a proxy for the quenched population, we find that the fraction of red galaxies increases with the environmental overdensity and with the stellar mass M * , consistent with previous works. As at lower redshift, the red fraction appears to be separable in mass and environment, suggesting the action of two processes: mass m ( M * ) and environmental () quenching. The parameters describing these appear to be essentially the same at z  ~ 0.7 as locally. We explore the relation between red fraction, mass and environment also for the central and satellite galaxies separately, paying close attention to the effects of impurities in the central-satellite classification and using carefully constructed samples well matched in stellar mass. There is little evidence for a dependence of the red fraction of centrals on overdensity. Satellites are consistently redder at all overdensities, and the satellite quenching efficiency, sat (, M * ), increases with overdensity at 0.1 〈 z  〈 0.4. This is less marked at higher redshift, but both are nevertheless consistent with the equivalent local measurements. At a given stellar mass, the fraction of galaxies that are satellites, f sat (, M * ), also increases with overdensity. The obtained ()/ f sat (, M * ) agrees well with sat (, M * ), demonstrating that the environmental quenching in the overall population is consistent with being entirely produced by a satellite quenching process at least up to z  = 0.7. However, despite the unprecedented size of our high-redshift samples, the associated statistical uncertainties are still significant and our statements should be understood as approximations to physical reality, rather than physically exact formulae.

Description: We study the linear thermal instability of a self-gravitating cloud, including the Hall effect and ambipolar diffusion, when the unperturbed state is subject to global cooling and expansion. We derive the eighth-order characteristic equation, which, in the absence of the self-gravity, expansion and other added effects, leads to the prior characteristic equations. The new criteria for thermal instability show that the background expansion (but not self-gravity) stabilizes the medium, but each of these diffusion mechanisms can destabilize the system for some of the angles. We find that self-gravity has a destabilizing effect on the isobaric thermal mode. When non-ideal effects are neglected, the stabilizing effect of the magnetic field might be reduced by the self-gravity for the wave vectors normal to the magnetic field vector. The effect of diffusion mechanisms on an expanding medium with self-gravity is similar to that on a medium without expansion and self-gravity. We can conclude that structures can form along the direction of the magnetic field lines.

Description: We present a novel, general-purpose method for deconvolving and denoizing images from gridded radio interferometric visibilities using Bayesian inference based on a Gaussian process model. The method automatically takes into account incomplete coverage of the uv -plane, signal mode coupling due to the primary beam and noise mode coupling due to uv sampling. Our method uses Gibbs sampling to efficiently explore the full posterior distribution of the underlying signal image given the data. We use a set of widely diverse mock images with a realistic interferometer set-up and level of noise to assess the method. Compared to results from a proxy for point source-based clean method we find that in terms of rms error and signal-to-noise ratio our approach performs better than traditional deconvolution techniques, regardless of the structure of the source image in our test suite. Our implementation scales as $\mathcal {O}(n_{\rm p} \log n_{\rm p})$ provides full statistical and uncertainty information of the reconstructed image, requires no supervision and provides a robust, consistent framework for incorporating noise and parameter marginalizations and foreground removal.

Description: We are now moving into an era where multi-object wide-field surveys, which traditionally use single fibres to observe many targets simultaneously, can exploit compact integral field units (IFUs) in place of single fibres. Current multi-object integral field instruments such as Sydney-AAO Multi-object Integral field spectrograph have driven the development of new imaging fibre bundles (hexabundles) for multi-object spectrographs. We have characterized the performance of hexabundles with different cladding thicknesses and compared them to that of the same type of bare fibre, across the range of fill fractions and input f-ratios likely in an IFU instrument. Hexabundles with 7-cores and 61-cores were tested for focal ratio degradation (FRD), throughput and cross-talk when fed with inputs from F/3.4 to 〉F/8. The five 7-core bundles have cladding thickness ranging from 1 to 8 μm, and the 61-core bundles have 5 μm cladding. As expected, the FRD improves as the input focal ratio decreases. We find that the FRD and throughput of the cores in the hexabundles match the performance of single fibres of the same material at low input f-ratios. The performance results presented can be used to set a limit on the f-ratio of a system based on the maximum loss allowable for a planned instrument. Our results confirm that hexabundles are a successful alternative for fibre imaging devices for multi-object spectroscopy on wide-field telescopes and have prompted further development of hexabundle designs with hexagonal packing and square cores.

Description: The detached-binary channel is an important channel for the formation of contact binaries, according to which a detached binary might evolve into contact by evolutionary expansion of the components, or angular momentum loss through the effect of magnetic braking. We have carried out a detailed binary population synthesis study of this channel, and obtained the parameter regions for detached binaries to evolve into contact. Combining the observations from the Kepler satellite with our results, we found that the ratio of the birth rate of the progenitors of contact binaries to that of contact binaries is greater than about 1.2. This suggests that for the detached-binary channel, the progenitors can be sufficient to produce observed contact binaries. In this channel, we find that the distribution of orbital period for contact binaries has a peak at about 0.25 d and a tail extending to longer periods, and the formation time-scale of contact binaries has a large range from ~1 Myr to 15 Gyr. These results show that the detached-binary channel could explain satisfactorily the main observational characteristics of contact binaries, in particular the distribution of orbital period shown by the Kepler observations and the existence of very young contact binaries.

Description: We investigate the problem of predicting the halo mass function from the properties of the Lagrangian density field. We focus on a perturbation spectrum with a small-scale cut-off (as in warm dark matter cosmologies). This cut-off results in a strong suppression of low-mass objects, providing additional leverage to rigorously test which perturbations collapse and to what mass. We find that all haloes are consistent with forming near peaks of the initial density field, with a strong correlation between protohalo density and ellipticity. We demonstrate that, while standard excursion set theory with correlated steps completely fails to reproduce the mass function, the inclusion of the peaks constraint leads to the correct number of haloes but significantly underpredicts the masses of low-mass objects (with the predicted halo mass function at low masses behaving like d n /d ln m  ~ m 2/3 ). This prediction is very robust and cannot be easily altered within the framework of a single collapse barrier. The nature of collapse in the presence of a small-scale cut-off thus reveals that excursion set calculations require a more detailed understanding of the collapse-time of a general ellipsoidal perturbation to predict the ultimate collapsed mass of a peak – a problem that has been hidden in the large abundance of small-scale structure in cold dark matter. We demonstrate how this problem can be resolved within the excursion set framework.

Description: We present a search for transient and variable radio sources at 154 MHz with the Murchison Widefield Array 32-tile prototype. 51 images were obtained that cover a field of view of 1430 deg 2 centred on Hydra A. The observations were obtained over three days in 2010 March and three days in 2011 April and May. The mean cadence of the observations was 26 min and there was additional temporal information on day and year time-scales. We explore the variability of a sample of 105 low-frequency radio sources within the field. Four bright ( S  〉 6 Jy) candidate variable radio sources were identified that displayed low levels of short time-scale variability (26 min). We conclude that this variability is likely caused by simplifications in the calibration strategy or ionospheric effects. On the time-scale of 1 yr we find two sources that show significant variability. We attribute this variability to either refractive scintillation or intrinsic variability. No radio transients were identified and we place an upper limit on the surface density of sources  〈 7.5 10 –5  deg –2 with flux densities 〉5.5 Jy, and characteristic time-scales of both 26 min and 1 yr.

Description: Extended emission (EE) is a high-energy, early time rebrightening sometimes seen in the light curves of short gamma-ray bursts (GRBs). We present the first contiguous fits to the EE tail and the later X-ray plateau seen by the Swift mission, unified within a single model. Our central engine is a magnetar surrounded by a fall-back accretion disc, formed by either the merger of two compact objects or the accretion-induced collapse of a white dwarf. During the EE phase, material is accelerated to super-Keplarian velocities and ejected from the system by the rapidly rotating ( P 1–10 ms) and very strong (10 15 G) magnetic field in a process known as magnetic propellering. The X-ray plateau is modelled as magnetic dipole spin-down emission. We first explore the range of GRB phenomena that the propeller could potentially reproduce, using a series of template light curves to devise a classification scheme based on phenomology. We then obtain fits to the light curves of nine GRBs with EE, simultaneously fitting both the propeller and the magnetic dipole spin-down and finding typical disc masses of a few 10 –3 M to a few 10 –2 M . This is done for ballistic, viscous disc and exponential accretion rates. We find that the conversion efficiency from kinetic energy to EM emission for propellered material needs to be 10 per cent and that the best-fitting results come from an exponential accretion profile.

Description: Quasar spectra reveal a rich array of important astrophysical information about galaxies which intersect the quasar line of sight. They also enable tests of the variability of fundamental constants over cosmological time- and distance-scales. Key to these endeavours are the laboratory frequencies, isotopic and hyperfine structures of various metal-ion transitions. Here, we review and synthesize the existing information about these quantities for 43 transitions which are important for measuring possible changes in the fine-structure constant, α, using optical quasar spectra, i.e. those of Na, Mg, Al, Si, Ca, Cr, Mn, Fe, Ni and Zn. We also summarize the information currently missing that precludes more transitions being used. We present an up-to-date set of coefficients, q , which define the sensitivity of these transitions to variations in α. New calculations of isotopic structures and q -coefficients are performed for ${\rm Si\,{\small{ II}}}$ and ${\rm Ti\,{\small{ II}}}$ , including ${\rm Si\,\small{ II}}$ 1808 and ${\rm Ti\,{\small{ II}}}$ 1910.6/1910.9 for the first time. Finally, simulated absorption-line spectra are used to illustrate the systematic errors expected if the isotopic/hyperfine structures are omitted from profile fitting analyses. To ensure transparency, repeatability and currency of the data and calculations, we supply a comprehensive data base as Supporting Information. This will be updated as new measurements and calculations are performed.

Description: We investigate how ram pressure of intragroup and intracluster medium can influence the spatial and temporal variations of star formation (SF) of disc galaxies with halo masses ( M h ) ranging from 10 10 to 10 12 M (i.e. from dwarf irregular to Milky Way-type) in groups and clusters with 10 13 ≤ M h /M ≤ 10 15 by using numerical simulations with a new model for time-varying ram pressure. The long-term evolution of SF rates and Hα morphologies corresponding to the distributions of star-forming regions are particularly investigated for different model parameters. The principal results are as follows. Whether ram pressure can enhance or reduce SF depends on M h of disc galaxies and inclination angles of gas discs with respect to their orbital directions for a given orbit and a given environment. For example, SF can be moderately enhanced in disc galaxies with M h  = 10 12 M at the pericentre passages in a cluster with M h  = 10 14 M whereas it can be completely shut down (‘quenching’) for low-mass discs with M h  = 10 10 M . Ram pressure can reduce the Hα-to-optical-disc-size ratios of discs and the level of the reduction depends on M h and orbits of disc galaxies for a given environment. Disc galaxies under strong ram pressure show characteristic Hα morphologies such as ring-like, one-sided and crescent-like distributions.

Description: We present initial results from the Jubilee Integrated Sachs-Wolfe (ISW) project, which models the expected cold dark matter ISW effect in the Jubilee simulation. The simulation volume is (6 h –1 Gpc) 3 , allowing power on very large scales to be incorporated into the calculation. Haloes are resolved down to a mass of 1.5 10 12 h –1 M , which allows us to derive a catalogue of mock Luminous Red Galaxies (LRGs) for cross-correlation analysis with the ISW signal. We find the ISW effect observed on a projected sky to grow stronger at late times with the evolution of the ISW power spectrum matching expectations from linear theory. Maps of the gravitational-lensing effect are calculated using the same potential as for the ISW. We calculate the redshift dependence of the ISW–LRG cross-correlation signal for a full-sky survey with no noise considerations. For  〈 30, the signal is strongest for lower redshift bins ( z  ~ 0.2–0.5), whereas for  〉 30, the signal is best observed with surveys covering z  ~ 0.6–1.0.

Description: Multifrequency Very Long Baseline Array (VLBA) observations were performed to study the radio morphology and synchrotron spectra of four high-frequency peaking radio sources. They are resolved into several compact components and the radio emission is dominated by hotspots/lobes. The core region is detected unambiguously in J1335+5844 and J1735+5049. The spectra of the main source components peak above 3 GHz. Assuming that the spectral peak is produced by synchrotron self-absorption, we estimate the magnetic field directly from observable quantities: in half of the components it agrees with the equipartition field, while in the others the difference exceeds an order of magnitude. By comparing the physical properties of the targets with those of larger objects, we found that the luminosity increases with linear size for sources smaller than a few kpc, while it decreases for larger objects. The asymmetric sources J1335+5844 and J1735+5049 suggest that the ambient medium is inhomogeneous and is able to influence the evolution of the radio emission even during its first stages. The core luminosity increases with linear size for sources up to a few kpc, while it seems constant for larger sources, suggesting an evolution independent of source total luminosity.

Description: In this work, we carry out an analysis of the observed times of primary and secondary eclipses of the post-common envelope binary NSVS 14256825. Recently, Almeida, Jablonski and Rodrigues proposed that two circumbinary companions orbit this short-period eclipsing binary, in order to explain observed variations in the timing of mutual eclipses between the two binary components. Using a standard weighted least-squares minimization technique, we have extensively explored the topology of 2 parameter space of a single planet model. We find the data set to be insufficient to reliably constrain a one-companion model. Various models, each with similar statistical significance, result in substantially different orbital architectures for the additional companion. No evidence is seen for a second companion of planetary nature. We suspect insufficient coverage (baseline) of timing data causing the best-fitting parameters to be unconstrained.

Description: We have studied the interstellar extinction in a field of ~ 3 arcmin x 3 arcmin located about 6 arcmin southwest of 30 Doradus in the Large Magellanic Cloud (LMC). Hubble Space Telescope observations in the U , B , V , I and Hα bands reveal patchy extinction in this field. The colour–magnitude diagram (CMD) shows an elongated stellar sequence, almost parallel to the main sequence (MS), which is in reality made up of stars of the red giant clump (RC) spread across the CMD by the uneven levels of extinction in this region. Since these objects are all at the same distance from us and share very similar physical properties, we can derive quantitatively both the extinction law in the range 3000–8000 Å and the absolute extinction towards about 100 objects, setting statistically significant constraints on the dust grains properties in this area. We find an extinction curve considerably flatter than the standard Galactic one and than those obtained before for the LMC. The derived value of R V  = 5.6 ± 0.3 implies that in this region larger grains dominate. Upper MS stars span a narrower range of E ( B – V ) values than RC objects, at variance with what has been found elsewhere in the LMC.

Description: Heavily obscured and Compton-thick active galactic nuclei (AGNs) are missing even in the deepest X-ray surveys, and indirect methods are required to detect them. Here we use a combination of the XMM–Newton serendipitous X-ray survey with the optical Sloan Digital Sky Survey (SDSS), and the infrared WISE all-sky survey in order to check the efficiency of the low X-ray-to-infrared luminosity selection method in finding heavily obscured AGNs. We select the sources which are detected in the hard X-ray band (2–8 keV), and also have a redshift determination (photometric or spectroscopic) in the SDSS catalogue. We match this sample with the WISE catalogue, and fit the spectral energy distributions of the 2844 sources which have three, or more, photometric data points in the infrared. We then select the heavily obscured AGN candidates by comparing their 12 μm luminosity to the observed 2–10 keV X-ray luminosity and the intrinsic relation between the X-ray and the mid-infrared luminosities. With this approach, we find 20 candidate heavily obscured AGNs and we then examine their X-ray and optical spectra. Of the 20 initial candidates, we find nine (64 per cent; out of the 14, for which X-ray spectra could be fitted) based on the X-ray spectra, and seven (78 per cent; out of the nine detected spectroscopically in the SDSS) based on the [O iii ] line fluxes. Combining all criteria, we determine the final number of heavily obscured AGNs to be 12–19, and the number of Compton-thick AGNs to be 2–5, showing that the method is reliable in finding obscured AGNs, but not Compton thick. However, those numbers are smaller than what would be expected from X-ray background population synthesis models, which demonstrates how the optical–infrared selection and the scatter of the L x - L MIR relation limit the efficiency of the method. Finally, we test popular obscured AGN selection methods based on mid-infrared colours, and find that the probability of an AGN to be selected by its mid-infrared colours increases with the X-ray luminosity. The (observed) X-ray luminosities of heavily obscured AGNs are relatively low ( $L_{\rm 2{\rm -}10\,keV} 〈 10^{44}\,{\rm erg\,s^{-1}}$ ), even though most of them are located in the ‘quasi stellar object (QSO) locus’. However, a selection scheme based on a relatively low X-ray luminosity and mid-infrared colours characteristic of QSOs would not select ~25 per cent of the heavily obscured AGNs of our sample.

Description: We combine cosmological, hydrodynamical simulations with accurate radiative transfer corrections to investigate the relation between strong ${{\rm H}\,\small{I}}$ absorbers ( ${N_{\rm {H}\,\small{I}}}\gtrsim 10^{17}\,{\rm cm^{-2}}$ ) and galaxies at redshift z  = 3. We find a strong anticorrelation between the column density and the impact parameter that connects the absorber to the nearest galaxy. The median impact parameters for Lyman Limit (LL) and Damped Lyman α systems (DLAs) are ~10 and ~1 proper kpc, respectively. If normalized to the size of the halo of the nearest central galaxy, the median impact parameters for LL and DLA systems become ~1 and ~10 –1 virial radii, respectively. At a given ${{\rm H}\,\small{I}}$ column density, the impact parameter increases with the mass of the closest galaxy, in agreement with observations. We predict most strong ${{\rm H}\,\small{I}}$ absorbers to be most closely associated with extremely low-mass galaxies, M * 〈 10 8 M and star formation rate 〈 10 – 1 M yr – 1 . We also find a correlation between the column density of absorbers and the mass of the nearest galaxy. This correlation is most pronounced for DLAs with ${N_{\rm {H}\,\small{I}}} 〉 10^{21} \,{\rm cm^{-2}}$ which are typically close to galaxies with M * 10 9 M . Similar correlations exist between column density and other properties of the associated galaxies such as their star formation rates, halo masses and ${{\rm H}\,\small{I}}$ content. The galaxies nearest to ${{\rm H}\,\small{I}}$ absorbers are typically far too faint to be detectable with current instrumentation, which is consistent with the high rate of (often unpublished) non-detections in observational searches for the galaxy counterparts of strong ${{\rm H}\,{\small {I}}}$ absorbers. Moreover, we predict that the detected nearby galaxies are typically not the galaxies that are most closely associated with the absorbers; thus, causing the impact parameters, star formation rates and stellar masses of the observed counterparts to be biased high.

Description: We examine substructure and mass segregation in the massive OB association Cygnus OB2 to better understand its initial conditions. Using a well-understood Chandra X-ray selected sample of young stars, we find that Cyg OB2 exhibits considerable physical substructure and has no evidence for mass segregation, both indications that the association is not dynamically evolved. Combined with previous kinematical studies we conclude that Cyg OB2 is dynamically very young, and what we observe now is very close to its initial conditions: Cyg OB2 formed as a highly substructured, unbound association with a low volume density (〈100 stars pc –3 ). This is inconsistent with the idea that all stars form in dense, compact clusters. The massive stars in Cyg OB2 show no evidence for having formed particularly close to one another, nor in regions of higher than average density. Since Cyg OB2 contains stars as massive as ~100 M , this result suggests that very massive stars can be born in relatively low-density environments. This would imply that massive stars in Cyg OB2 did not form by competitive accretion, or by mergers.

Description: The X-ray transient IGR J18245–2452 in the globular cluster M28 contains the first neutron star (NS) seen to switch between rotation-powered and accretion-powered pulsations. We analyse its 2013 March–April 25 d long outburst as observed by Swift , which had a peak bolometric luminosity of ~6 per cent of the Eddington limit ( L Edd ), and give detailed properties of the thermonuclear burst observed on 2013 April 7. We also present a detailed analysis of new and archival Chandra data, which we use to study quiescent emission from IGR J18245–2452 between 2002 and 2013. Together, these observations cover almost five orders of magnitude in X-ray luminosity ( L X , 0.5–10 keV). The Swift spectrum softens during the outburst decay (photon index from 1.3 above L X / L Edd  = 10 –2 to ~2.5 at L X / L Edd  = 10 –4 ), similar to other NS and black hole transients. At even lower luminosities, L X / L Edd  = [10 –4 –10 –6 ], deep Chandra observations reveal hard ( = 1–1.5), purely non-thermal and highly variable X-ray emission in quiescence. We therefore find evidence for a spectral transition at L X / L Edd ~ 10 –4 , where the X-ray spectral softening observed during the outburst decline turns into hardening as the source goes to quiescence. Furthermore, we find a striking variability pattern in the 2008 Chandra light curves: rapid switches between a high-luminosity ‘active’ state ( L X ~= 3.9 10 33 erg s –1 ) and a low-luminosity ‘passive’ state ( L X ~= 5.6 10 32 erg s –1 ), with no detectable spectral change. We put our results in the context of low-luminosity accretion flows around compact objects and X-ray emission from millisecond radio pulsars. Finally, we discuss possible origins for the observed mode switches in quiescence, and explore a scenario where they are caused by fast transitions between the magnetospheric accretion and pulsar wind shock emission regimes.

Description: We investigated the spectral and timing properties of the type B quasi-periodic oscillations (QPOs) showing up in the transient black hole binary GX 339-4 during its four outbursts observed by Rossi X-ray Timing Explorer (RXTE)/PCA and HEXTE in 2002, 2004, 2007 and 2010. We find that, the dependence on variability of the accretion flow turns out to be similar for the type B QPOs occurring in these four outbursts. We therefore take the results from the 2010 outburst for presentation. Our spectral results obtained from both the energy and time domains show that, the occurrence of the type B QPO is accompanied with sudden increase of hard component flux, relatively smaller inner disk radius, stable disk but variable corona. The latter may be understood in a scenario of variable input of seed photons for Comptonization in the corona. Further clues to probing the possible origination of the type B QPO come from our analysis of time lag and its energy dependence. The energy dependence of type B QPO amplitude suggests that the hard component dominate the variability and the time lag spectral analysis results suggests the type B QPO could be related to inverse Compton scattering. The time lag between hard and soft energy band is about 10 ms and found to depend on frequency in a form of –0.7 for type B QPOs in the rising phase. Finally we put these results in a context of a blob mechanism at work.

Description: The bright binary system YZ Cassiopeiae is a remarkable laboratory for studying the Am phenomenon. It consists of a metallic-lined A2 star and an F2 dwarf on a circular orbit, which undergo total and annular eclipses. We present an analysis of 15 published light curves and 42 new high-quality échelle spectra, resulting in measurements of the masses, radii, effective temperatures and photospheric chemical abundances of the two stars. The masses and radii are measured to 0.5 per cent precision: M A  = 2.263 ± 0.012 M , M B  = 1.325 ± 0.007 M , R A  = 2.525 ± 0.011 R and R B  = 1.331 ± 0.006 R . We determine the abundance of 20 elements for the primary star, of which all except scandium are supersolar by up to 1 dex. The temperature of this star (9520 ± 120 K) makes it one of the hottest Am stars. We also measure the abundances of 25 elements for its companion ( T eff  = 6880 ± 240 K), finding all to be solar or slightly above solar. The photospheric abundances of the secondary star should be representative of the bulk composition of both stars. Theoretical stellar evolutionary models are unable to match these properties: the masses, radii and temperatures imply a half-solar chemical composition ( Z  = 0.009 ± 0.003) and an age of 490–550 Myr. YZ Cas therefore presents a challenge to stellar evolutionary theory.

Description: We present the result of the cross-matching between ultraviolet (UV)-excess sources selected from the UV-Excess Survey of the Northern Galactic Plane (UVEX) and several infrared (IR) surveys (2MASS, UKIDSS and WISE ). From the position in the ( J  –  H ) versus ( H  –  K ) colour–colour diagram, we select UV-excess candidate white dwarfs with an M-dwarf type companion, candidates that might have a lower mass, brown-dwarf type companion and candidates showing an IR-excess only in the K band, which might be due to a debris disc. Grids of reddened DA+dM and sdO+MS/sdB+MS model spectra are fitted to the U , g , r , i , z , J , H , K photometry in order to determine spectral types and estimate temperatures and reddening. From a sample of 964 hot candidate white dwarfs with ( g  –  r ) 〈 0.2, the spectral energy distribution fitting shows that ~2–4 per cent of the white dwarfs have an M-dwarf companion, ~2 per cent have a lower-mass companion, and no clear candidates for having a debris disc are found. Additionally, from WISE six UV-excess sources are selected as candidate quasi-stellar objects (QSOs). Two UV-excess sources have a WISE IR-excess showing up only in the mid-IR W 3 band of WISE , making them candidate luminous infrared galaxies (LIRGs) or Sbc starburst galaxies.

Description: We demonstrate that optical data from Sloan Digital Sky Survey, X-ray data from ROSAT and Chandra , and Sunyaev–Zel'dovich (SZ) data from Planck can be modelled in a fully self-consistent manner. After accounting for systematic errors and allowing for property covariance, we find that scaling relations derived from optical and X-ray selected cluster samples are consistent with one another. Moreover, these cluster scaling relations satisfy several non-trivial spatial abundance constraints and closure relations. Given the good agreement between optical and X-ray samples, we combine the two and derive a joint set of L X - M and Y SZ - M relations. Our best-fitting Y SZ - M relation is in good agreement with the observed amplitude of the thermal SZ power spectrum for a Wilkinson Microwave Anisotropy Probe 7 cosmology, and is consistent with the masses for the two CLASH galaxy clusters published thus far. We predict the halo masses of the remaining z ≤ 0.4 CLASH clusters, and use our scaling relations to compare our results with a variety of X-ray and weak lensing cluster masses from the literature.

Description: From a volume-limited sample of 45 542 galaxies and 6000 groups with z  ≤ 0.213, we use an adapted minimal spanning tree algorithm to identify and classify large-scale structures within the Galaxy And Mass Assembly (GAMA) survey. Using galaxy groups, we identify 643 filaments across the three equatorial GAMA fields that span up to 200 h –1 Mpc in length, each with an average of eight groups within them. By analysing galaxies not belonging to groups, we identify a secondary population of smaller coherent structures composed entirely of galaxies, dubbed ‘tendrils’ that appear to link filaments together, or penetrate into voids, generally measuring around 10 h –1 Mpc in length and containing on average six galaxies. Finally, we are also able to identify a population of isolated void galaxies. By running this algorithm on GAMA mock galaxy catalogues, we compare the characteristics of large-scale structure between observed and mock data, finding that mock filaments reproduce observed ones extremely well. This provides a probe of higher order distribution statistics not captured by the popularly used two-point correlation function.

Description: We explore the dependence of the galaxy mass-metallicity relation on environment in SDSS, in terms of both over-density and central/satellite dichotomy. We find that at a given stellar mass, there is a strong dependence of metallicity on over-density for star-forming satellites (i.e. all galaxies members of groups/clusters which are not centrals). High metallicity satellites reside, on average, in regions four times denser than the low metallicity ones. Instead, for star-forming centrals no correlation is found. Star-forming satellites at different stellar masses form a tight sequence in the average over-density – metallicity plane, which covers the entire observed range of metallicities and stellar masses. This remarkable result appears to imply that there exists a universal evolutionary path for all star-forming satellites, regardless of their stellar masses. The strong correlation between over-density and metallicity for star-forming satellites indicates that the gas inflow of satellite galaxies is progressively metal-enriched in denser regions. We interpret our results by employing the gas regulator model and find that the metallicity of the enriched inflow of star-forming satellite galaxies, Z 0, sat , strongly increases with increasing over-density. The derived Z 0, sat – overdensity relation is largely independent of stellar mass and can be well described by a simple power law. If the metallicity of the inflow of star-forming satellites can represent the metallicity of the IGM, then the implied metallicity of the IGM rises from ~0.01 Z in the void-like environment to ~0.3 Z in the cluster-like environment, in broad agreement with observations. We show that the observed metallicity difference between star-forming centrals and star-forming satellites becoming smaller towards high stellar masses can be simply explained by the mass-independent enriched inflow, without the need to involve any mass-dependent environmental effect on metallicity. Since satellite galaxies account for at least half of the galaxy population, our findings prompt for a revision of many galaxy evolutionary models, which generally assume pristine gas inflows.