ALBERT

Description: We present measurements of higher order clustering of galaxies in the latest release of the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS)-Wide. We construct a series of volume-limited sample of galaxies containing more than one million galaxies over the redshift range 0.2 〈  z  〈 1 in the four independent fields of the CFHTLS-Wide. Using a counts-in-cells technique we measure the variance ${\bar{\xi }}_2$ and the hierarchical moments $S_{n}= {{\bar{\xi }}_n / {\bar{\xi }}_2^{n-1}}$ (3 ≤  n  ≤ 5) as a function of redshift and angular scale. We find that the measured field-to-field scatter in our estimators is in excellent agreement with analytical predictions. At small scales, corresponding to the highly non-linear regime, we find tentative evidence at the 1 level that the hierarchical moments increase with redshift. At large scales, corresponding to the weakly non-linear regime, our measurements are marginally consistent with perturbation theory predictions for standard cold dark matter cosmology using a simple linear bias. The predictions of perturbation theory tend to slightly overestimate our measurements, which may be a signature of non-linear bias.

Description: We estimate cosmic microwave background (CMB) polarization power spectra and temperature–polarization cross-spectra, from the 9-year data of the Wilkinson Microwave Anisotropy Probe ( WMAP ). Foreground cleaning is implemented using minimum variance linear combinations of the coefficients of needlet decompositions of sky maps for all WMAP channels, to produce maps for CMB temperature anisotropies ( T -mode) and polarization ( E and B -modes), for nine different years of observation. The final power spectra are computed from averages of all possible cross-year power spectra obtained using foreground-cleaned maps for the different years. Our analysis technique yields a measurement of the EE spectrum that is in excellent agreement with theoretical expectations from the current cosmological model. By comparison, the publicly available WMAP EE power spectrum is higher on average (and significantly higher than the predicted EE spectrum from the current best fit) at scales larger than about a degree, an excess that is not confirmed by our analysis. Our TE and TB measurements are in good agreement overall with the WMAP ones and are compatible with the theoretical expectations, although a few data points are off by a few standard deviations, and yield a reduced 2 somewhat above expectation. As predicted for a standard cosmological model with low tensor-to-scalar ratio, the EB and BB power spectra obtained in our analysis are compatible with zero.

Description: We present optical integral field unit observations of two gas pillars surrounding the Galactic young massive star cluster NGC 3603. The high S/N and spectral resolution of these data have allowed us to accurately quantify the Hα, [N ii ] and [S ii ] emission line shapes, and we find a mixture of broad (FWHM ~ 70–100 km s –1 ) and narrow (〈50 km s –1 ) components. The broad components are found close to the edges of both pillars, suggesting that they originate in turbulent mixing layers (TMLs) driven by the effect of the star cluster wind. Both pillars exhibit surprisingly high ionized gas densities of 〉10 000 cm –3 . In one pillar we found that these high densities are only found in the narrow component, implying that they must originate from deeper within the pillar than the broad component. From this, together with our kinematical data, we conclude that the narrow component traces a photoevaporation flow, and that the TML forms at the interface with the hot wind. On the pillar surfaces, we find a consistent offset in radial velocity between the narrow (brighter) components of Hα and [N ii ] of ~5–8 km s –1 , for which we were unable to find a satisfactory explanation. We urge the theoretical community to simulate mechanical and radiative cloud interactions in more detail to address the many unanswered questions raised by this study.

Description: By exploiting the data base of early-type galaxy (ETG) members of the WINGS survey of nearby clusters, we address here the long debated question of the origin and shape of the Fundamental Plane (FP). Our data suggest that different physical mechanisms concur in shaping and ‘tilting’ the FP with respect to the virial plane (VP) expectation. In particular, a ‘hybrid solution’ in which the structure of galaxies and their stellar population are the main contributors to the FP tilt seems to be favoured. We find that the bulk of the tilt should be attributed to structural non-homology, while stellar population effects play an important but less crucial role. In addition, our data indicate that the differential FP tilt between the V and K band is due to a sort of entanglement between structural and stellar population effects, for which the inward steepening of colour profiles ( V  –  K ) tends to increase at increasing the stellar mass of ETGs. The same kind of analysis applied to the ATLAS 3 D and Sloan Digital Sky Survey (SDSS) data in common with WINGS ( WSDSS throughout the paper) confirms our results, the only remarkable difference being the less important role that our data attribute to the stellar mass-to-light-ratio (stellar populations) in determining the FP tilt . The ATLAS 3 D data also suggest that the FP tilt depends as well on the dark matter (DM) fraction and on the rotational contribution to the kinetic energy ( V rot /), thus again pointing towards the above-mentioned ‘hybrid solution’. We show that the global properties of the FP, i.e. its tilt and tightness, can be understood in terms of the underlying correlation among mass, structure and stellar population of ETGs, for which, at increasing the stellar mass, ETGs become (on average) ‘older’ and more centrally concentrated. Finally, we show that a Malmquist-like selection effect may mimic a differential evolution of the mass-to-light ratio for galaxies of different masses. This should be taken into account in the studies investigating the amount of the so-called ‘downsizing’ phenomenon.

Description: I present a new algorithm, Curved-sky grAvitational Lensing for Cosmological Light conE simulatioNS ( calclens ), for efficiently computing weak gravitational lensing shear signals from large N -body light cone simulations over a curved sky. This new algorithm properly accounts for the sky curvature and boundary conditions, is able to produce redshift-dependent shear signals including corrections to the Born approximation by using multiple-plane ray tracing and properly computes the lensed images of source galaxies in the light cone. The key feature of this algorithm is a new, computationally efficient Poisson solver for the sphere that combines spherical harmonic transform and multigrid methods. As a result, large areas of sky (~10 000 square degrees) can be ray traced efficiently at high resolution using only a few hundred cores. Using this new algorithm and curved-sky calculations that only use a slower but more accurate spherical harmonic transform Poisson solver, I study the convergence, shear E-mode, shear B-mode and rotation mode power spectra. Employing full-sky E/B-mode decompositions, I confirm that the numerically computed shear B-mode and rotation mode power spectra are equal at high accuracy (1 per cent) as expected from perturbation theory up to second order. Coupled with realistic galaxy populations placed in large N -body light cone simulations, this new algorithm is ideally suited for the construction of synthetic weak lensing shear catalogues to be used to test for systematic effects in data analysis procedures for upcoming large-area sky surveys. The implementation presented in this work, written in c and employing widely available software libraries to maintain portability, is publicly available at http://code.google.com/p/calclens .

Description: Quasar accretion disc winds observed via broad absorption lines (BALs) in the UV produce strong continuous absorption in X-rays. The X-ray absorber is believed to serve critically as a radiative shield to keep the outflow ionizations low enough for radiative driving. However, previous studies have shown that ‘mini-BAL’ and narrow absorption line (NAL) outflows have dramatically less X-ray absorption than BALs. Here, we examine X-ray and rest-frame UV spectra of eight mini-BAL quasars with outflow speeds in the range 0.1–0.2c to test the hypothesis that these extreme speeds require a strong shield. We find that the X-ray absorption is weak or moderate, with neutral-equivalent column densities N H  〈 few 10 22 cm –2 , consistent with mini-BALs at lower speeds. We use photoionization models to show that the amount of shielding consistent with our data is too weak to control the outflow ionizations and, therefore, it is not important for the acceleration. Shielding in complex geometries also seems unlikely because the alleged shield would need to extinguish the ionizing far-UV flux while avoiding detection in X-rays and the near-UV. We argue that the outflow ionizations are kept moderate, instead, by high gas densities in small clouds. If the mini-BALs form at radial distances of the order of R ~ 2 pc from the central quasar (broadly consistent with theoretical models and with the mini-BAL variabilities observed here and in previous work), and the total column densities in the mini-BAL gas are N H 10 21 cm –2 , then the total radial extent of outflow clouds is only R clouds 3 x 10 13 cm in cases of no/weak shielding or R clouds 3 x 10 14 cm behind the maximum shield allowed by our data. This implies radial filling factors R clouds / R 5 x 10 – 6 or 5 x 10 – 5 for the unshielded or maximally shielded cases, respectively. Compared to the transverse sizes 8 x 10 15 cm (based on measured line depths), the outflows have shapes like thin ‘pancakes’ viewed face-on, or they occupy larger volumes like a spray of many dense clouds with a small volume filling factor. These results favour models with magnetic confinement in magnetic disc winds. To the extent that BALs, mini-BALs and NALs probe the same general outflow phenomenon, our result for dense substructures should apply to all three outflow types.

Description: The estimated stellar masses of galaxies are widely used to characterize how the galaxy population evolves over cosmic time. If stellar masses can be estimated in a robust manner, free from any bias, global diagnostics such as the stellar mass function can be used to constrain the physics of galaxy formation. We explore how galaxy stellar masses, estimated by fitting broad-band spectral energy distributions (SEDs) with stellar population models, can be biased as a result of commonly adopted assumptions for the star formation and chemical enrichment histories, recycled fractions and dust attenuation curves of galaxies. We apply the observational technique of broad-band SED fitting to model galaxy SEDs calculated by the theoretical galaxy formation model GALFORM, isolating the effect of each of these assumptions. We find that, averaged over the entire galaxy population, the common assumption of exponentially declining star formation histories does not, by itself, adversely affect stellar mass estimation. However, we also show that this result does not hold when considering galaxies that have undergone a recent burst of star formation. We show that fixing the metallicity in SED fitting or using sparsely sampled metallicity grids can introduce mass-dependent systematics into stellar mass estimates. We find that the common assumption of a star–dust geometry corresponding to a uniform foreground dust screen can cause the stellar masses of dusty model galaxies to be significantly underestimated. Finally, we show that stellar mass functions recovered by applying SED fitting to model galaxies at high redshift can differ significantly in both shape and normalization from the intrinsic mass functions predicted by a given model. In particular, the effects of dust can reduce the normalization at the high-mass end by up to 0.6 dex in some cases. Given these differences, our methodology of using stellar masses estimated from model galaxy SEDs offers a new, self-consistent way to compare model predictions with observations. We conclude that great care should be taken when comparing theoretical galaxy formation models to observational results based on the estimated stellar masses of high-redshift galaxies.

Description: We analyse the 2D correlation function of the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey (BOSS) CMASS sample of massive galaxies of the ninth data release to measure cosmic expansion H and the angular diameter distance D A at a mean redshift of 〈 z 〉 = 0.57. We apply, for the first time, a new correlation function technique called clustering wedges μ ( s ). Using a physically motivated model, the anisotropic baryonic acoustic feature in the galaxy sample is detected at a significance level of 4.7 compared to a featureless model. The baryonic acoustic feature is used to obtain model-independent constraints cz / H / r s = 12.28 ± 0.82 (6.7 percent accuracy) and D A / r s =  9.05 ± 0.27 (3.0 per cent) with a correlation coefficient of –0.5, where r s is the sound horizon scale at the end of the baryonic drag era. We conduct thorough tests on the data and 600 simulated realizations, finding robustness of the results regardless of the details of the analysis method. Combining this with r s constraints from the cosmic microwave background, we obtain H (0.57) = 90.8 ± 6.2 km s –1 Mpc –1 and D A (0.57) = 1386 ± 45 Mpc. We use simulations to forecast results of the final BOSS CMASS data set. We apply the reconstruction technique on the simulations demonstrating that the sharpening of the anisotropic baryonic acoustic feature should improve the detection as well as tighten constraints of H and D A by ~30 per cent on average.

Description: We present an analysis of Chandra archival, pre-explosion data of the positions of three nearby (〈25 Mpc) Type Ia supernovae, SN2011iv, SN2012cu and SN2012fr. No sources corresponding to the progenitors were found in any of the observations. Combining all sources with well-defined backgrounds does not reveal any evidence for X-ray emission from the progenitors either. We calculated upper limits on the bolometric luminosities of the progenitors, under the assumption that they were black bodies with effective temperatures between 30 and 150 eV, corresponding to ‘canonical’ supersoft X-ray sources. The upper limits of SN2012fr straddle the Eddington luminosity of canonical supersoft sources, but fainter canonical supersoft sources cannot be ruled out by this study. We also compare our upper limits with known compact binary supersoft X-ray sources. This study is a continuation of the campaign to directly detect or constrain the X-ray characteristics of pre-explosion observations of nearby Type Ia supernova progenitors; with the results reported in Nielsen, Voss & Nelemans (see reference in Introduction), the number of nearby Type Ia supernovae for which pre-explosion images are available in the Chandra archive is now 13 and counting.

Description: In this work, we report the Photodetector Array Camera and Spectrometer (PACS) 100 μm/160 μm detections of a sample of 42 GALEX -selected and far-infrared (FIR)-detected Lyman break galaxies (LBGs) at z  ~ 1 located in the Cosmic Evolution Survey (COSMOS) field and analyse their ultraviolet (UV) to FIR properties. The detection of these LBGs in the FIR indicates that they have a dust content high enough so that its emission can be directly detected. According to a spectral energy distribution (SED) fitting with stellar population templates to their UV-to-near-IR observed photometry, PACS-detected LBGs tend to be bigger ( R eff  ~ 4.1 kpc), more massive [log ( M * /M ) ~ 10.7], dustier [ E s ( B  –  V ) ~ 0.40], redder in the UV continuum (β ~ –0.60) and UV-brighter [log ( L UV /L ) ~ 10.1] than PACS-undetected LBGs. PACS-detected LBGs at z  ~ 1 are mostly disc-like galaxies and are located over the green valley and red sequence of the colour–magnitude diagram of galaxies at their redshift. By using their UV and IR emission, we find that PACS-detected LBGs tend to be less dusty and have slightly higher total star formation rates (SFRs) than other PACS-detected UV-selected galaxies within the same redshift range. As a consequence of the selection effect due to the depth of the FIR observations employed, all our PACS-detected LBGs have total IR luminosities, L IR , higher than 10 11 L and thus are luminous IR galaxies. However, none of the PACS-detected LBGs are in the ultra-luminous IR galaxy (ULIRG) regime, L IR  ≥ 10 12 L , where the FIR observations are complete. The finding of ULIRGs-LBGs at higher redshifts ( z  ~ 3) suggests an evolution of the FIR emission of LBGs with cosmic time. In an IRX–β diagram, PACS-detected LBGs at z  ~ 1 tend to be located around the relation for local starburst similarly to other UV-selected PACS-detected galaxies at the same redshift. Consequently, the dust-correction factors obtained with their UV continuum slope allow us to determine their total SFR, unlike at higher redshifts. However, the dust attenuation derived from UV to NIR SED fitting overestimates the total SFR for most of our PACS-detected LBGs in an age-dependent way: the overestimation factor is higher in younger galaxies. This is likely due to the typical degeneracy between dust attenuation and age in the SED fitting with synthetic templates and highlights the importance of the FIR measurements in the analysis of star-forming galaxies at intermediate redshifts.