ALBERT

Description: We present a dynamical analysis of the galaxy cluster AC114 based on a catalogue of 524 velocities. Of these, 169 (32 per cent) are newly obtained at European Southern Observatory (Chile) with the Very Large Telescope and the VIsible MultiObject spectrograph. Data on individual galaxies are presented and the accuracy of the measured velocities is discussed. Dynamical properties of the cluster are derived. We obtain an improved mean redshift value z  = 0.31665 ± 0.0008 and velocity dispersion $\sigma = 1893^{+73}_{-82}\ {\rm km\,s^{-1}}$ . A large velocity dispersion within the core radius and the shape of the infall pattern suggests that this part of the cluster is in a radial phase of relaxation with a very elongated radial filament spanning 12 000 km s –1 . A radial foreground structure is detected within the central 0.5  h –1  Mpc radius, recognizable as a redshift group at the same central redshift value. We analyse the colour distribution for this archetype Butcher–Oemler galaxy cluster and identify the separate red and blue galaxy sequences. The latter subset contains 44 per cent of confirmed members of the cluster, reaching magnitudes as faint as R f = 21.1 (1.0 mag fainter than previous studies). We derive a mass M 200  = (4.3 ± 0.7)  x 10 15 M   h –1 . In a subsequent paper, we will utilize the spectral data presented here to explore the mass–metallicity relation for this intermediate redshift cluster.

Description: We use the H ii galaxies L – relation and the resulting Hubble expansion cosmological probe of a sample of just 25 high- z (up to z ~ 2.33) H ii galaxies, in a joint likelihood analysis with other well tested cosmological probes (cosmic microwave background, CMB, Baryon Acoustic Oscillations, BAOs) in an attempt to constrain the dark energy equation of state (EoS). The constraints, although still weak, are in excellent agreement with those of a similar joint analysis using the well established SNIa Hubble expansion probe. Interestingly, even with the current small number of available high redshift H ii galaxies, the H ii /BAO/CMB joint analysis gives a 13 per cent improvement of the quintessence dark energy cosmological constraints compared to the BAO/CMB joint analysis. We have further performed extensive Monte Carlo simulations, with a realistic redshift sampling, to explore the extent to which the use of the L – relation, observed in H ii galaxies, can constrain effectively the parameter space of the dark energy EoS. The simulations predict substantial improvement in the constraints when increasing the sample of high- z H ii galaxies to 500, a goal that can be achieved in reasonable observing times with existing large telescopes and state-of-the-art instrumentation.

Description: We acquired spectra of 141 H  ii regions in 10 late-type low surface brightness galaxies (LSBGs). The analysis of the chemical abundances obtained from the nebular emission lines shows that metallicity gradients are a common feature of LSBGs, contrary to previous claims concerning the absence of such gradients in this class of galaxies. The average slope, when expressed in units of the isophotal radius, is found to be significantly shallower in comparison to galaxies of high surface brightness. This result can be attributed to the reduced surface brightness range measured across their discs, when combined with a universal surface mass density–metallicity relation. With a similar argument we explain the common abundance gradient observed in high surface brightness galaxy (HSBG) discs and its approximate dispersion. This conclusion is reinforced by our result that LSBGs share the same common abundance gradient with HSBGs, when the slope is expressed in terms of the exponential disc scalelength.

Description: The radially averaged metallicity distribution of the interstellar medium (ISM) and the young stellar population of a sample of 20 disc galaxies is investigated by means of an analytical chemical evolution model which assumes constant ratios of galactic wind mass-loss and accretion mass gain to star formation rate. Based on this model, the observed metallicities and their gradients can be described surprisingly well by the radially averaged distribution of the ratio of stellar mass to ISM gas mass. The comparison between observed and model-predicted metallicity is used to constrain the rate of mass-loss through galactic wind and accretion gain in units of the star formation rate. Three groups of galaxies are found: galaxies with either mostly winds and only weak accretion, or mostly accretion and only weak winds, and galaxies where winds are roughly balanced by accretion. The three groups are distinct in the properties of their gas discs. Galaxies with approximately equal rates of mass-loss and accretion gain have low metallicity, atomic-hydrogen-dominated gas discs with a flat spatial profile. The other two groups have gas discs dominated by molecular hydrogen out to 0.5 to 0.7 isophotal radii and show a radial exponential decline, which is on average steeper for the galaxies with small accretion rates. The rates of accretion ( 1.0 x SFR) and outflow ( 2.4 x SFR) are relatively low. The latter depend on the calibration of the zero-point of the metallicity determination from the use of H  ii region strong emission lines.

Description: We report the first results of a programme aimed at studying the properties of high-redshift galaxies with ongoing massive and dominant episodes of star formation (H ii galaxies). We use the L (Hβ)– distance estimator based on the correlation between the ionized gas velocity dispersions and Balmer emission line luminosities of H ii galaxies and Giant H ii regions to trace the expansion of the Universe up to z ~ 2.33. This approach provides an independent constraint on the equation of state of dark energy and its possible evolution with look-back time. Here we present high-dispersion (8000 to 10 000 resolution) spectroscopy of H ii galaxies at redshifts between 0.6 and 2.33, obtained at the Very Large Telescope (VLT) using XShooter. Using six of these H ii galaxies we obtain broad constraints on the plane m – w 0 . The addition of 19 high- z H ii galaxies from the literature improves the constraints and highlights the need for high-quality emission line profiles, fluxes and reddening corrections. The 25 high- z H ii galaxies plus our local compilation of 107 H ii galaxies up to z = 0.16 were used to impose further constraints. Our results are consistent with recent studies, although weaker due to the as yet small sample and low quality of the literature data of high- z H ii galaxies. We show that much better and competitive constraints can be obtained using a larger sample of high-redshift H ii galaxies with high quality data that can be easily obtained with present facilities like K-band Multi Object Spactrograph (KMOS) at the VLT.

Description: The Pan-STARRS1 (PS1) survey has obtained imaging in five bands ( griz y P1 ) over 10 Medium Deep Survey (MDS) fields covering a total of 70 square degrees. This paper describes the search for apparently hostless supernovae (SNe) within the first year of PS1 MDS data with an aim of discovering superluminous supernovae (SLSNe). A total of 249 hostless transients were discovered down to a limiting magnitude of M AB  ~ 23.5, of which 76 were classified as Type Ia supernovae (SNe Ia). There were 57 SNe with complete light curves that are likely core-collapse SNe (CCSNe) or type Ic SLSNe and 12 of these have had spectra taken. Of these 12 hostless, non-Type Ia SNe, 7 were SLSNe of type Ic at redshifts between 0.5 and 1.4. This illustrates that the discovery rate of type Ic SLSNe can be maximized by concentrating on hostless transients and removing normal SNe Ia. We present data for two possible SLSNe; PS1-10pm ( z  = 1.206) and PS1-10ahf ( z  = 1.1), and estimate the rate of type Ic SLSNe to be between $3^{+3}_{-2}\times 10^{-5}$ and $8^{+2}_{-1}\times 10^{-5}$ that of the CCSN rate within 0.3 ≤  z  ≤ 1.4 by applying a Monte Carlo technique. The rate of slowly evolving, type Ic SLSNe (such as SN2007bi) is estimated as a factor of 10 lower than this range.

Description: Superluminous supernovae (SLSNe) of Type Ic have a tendency to occur in faint host galaxies which are likely to have low mass and low metallicity. PTF12dam is one of the closest and best-studied superluminous explosions that has a broad and slowly fading light curve similar to SN 2007bi. Here we present new photometry and spectroscopy for PTF12dam from 200–500 d (rest frame) after peak and a detailed analysis of the host galaxy (SDSS J142446.21+461348.6 at z  = 0.107). Using deep templates and image subtraction we show that the light curve can be fit with a magnetar model if escape of high-energy gamma rays is taken into account. The full bolometric light curve from –53 to +399 d (with respect to peak) cannot be fit satisfactorily with the pair-instability models. An alternative model of interaction with a dense circumstellar material (CSM) produces a good fit to the data although this requires a very large mass (~13 M ) of hydrogen-free CSM. The host galaxy is a compact dwarf (physical size ~1.9 kpc) and with M g  = –19.33 ± 0.10, it is the brightest nearby SLSN Ic host discovered so far. The host is a low-mass system (2.8  x  10 8 M ) with a star formation rate (5.0 M  yr –1 ), which implies a very high specific star formation rate (17.9 Gyr –1 ). The remarkably strong nebular emission provide detections of the [O iii ] 4363 and [O ii ] 7320, 7330auroral lines and an accurate oxygen abundance of 12 + log (O/H) = 8.05 ± 0.09. We show here that they are at the extreme end of the metallicity distribution of dwarf galaxies and propose that low metallicity is a requirement to produce these rare and peculiar SNe.

Description: We present optical photometric and spectroscopic coverage of the superluminous supernova (SLSN) PS1-11ap, discovered with the Pan-STARRS1 Medium Deep Survey at z  = 0.524. This intrinsically blue transient rose slowly to reach a peak magnitude of M u  = –21.4 mag and bolometric luminosity of 8 10 43 erg s –1 before settling on to a relatively shallow gradient of decline. The observed decline is significantly slower than those of the SLSNe-Ic which have been the focus of much recent attention. Spectroscopic similarities with the lower redshift SN2007bi and a decline rate similar to 56 Co decay time-scale initially indicated that this transient could be a candidate for a pair instability supernova (PISN) explosion. Overall the transient appears quite similar to SN2007bi and the lower redshift object PTF12dam. The extensive data set, from 30 d before peak to 230 d after, allows a detailed and quantitative comparison with published models of PISN explosions. We find that the PS1-11ap data do not match these model explosion parameters well, supporting the recent claim that these SNe are not pair instability explosions. We show that PS1-11ap has many features in common with the faster declining SLSNe-Ic, and the light-curve evolution can also be quantitatively explained by the magnetar spin-down model. At a redshift of z  = 0.524, the observer-frame optical coverage provides comprehensive rest-frame UV data and allows us to compare it with the SLSNe recently found at high redshifts between z  = 2 and 4. While these high- z explosions are still plausible PISN candidates, they match the photometric evolution of PS1-11ap and hence could be counterparts to this lower redshift transient.

Description: We present deep echelle spectrophotometry of the brightest emission-line knots of the star-forming galaxies He 2–10, Mrk 1271, NGC 3125, NGC 5408, POX 4, SDSS J1253–0312, Tol 1457–262, Tol 1924–416 and the H ii region Hubble V in the Local Group dwarf irregular galaxy NGC 6822. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100–10420 Å range. We determine electron densities and temperatures of the ionized gas from several emission-line intensity ratios for all the objects. We derive the ionic abundances of C 2+ and/or O 2+ from faint pure recombination lines in several of the objects, permitting to derive their C/H and C/O ratios. We have explored the chemical evolution at low metallicities analysing the C/O versus O/H, C/O versus N/O and C/N versus O/H relations for Galactic and extragalactic H ii regions and comparing with results for Galactic halo stars and damped Lyα systems. We find that H ii regions in star-forming dwarf galaxies occupy a different locus in the C/O versus O/H diagram than those belonging to the inner discs of spiral galaxies, indicating their different chemical evolution histories, and that the bulk of C in the most metal-poor extragalactic H ii regions should have the same origin than in halo stars. The comparison between the C/O ratios in H ii regions and in stars of the Galactic thick and thin discs seems to give arguments to support the merging scenario for the origin of the Galactic thick disc. Finally, we find an apparent coupling between C and N enrichment at the usual metallicities determined for H ii regions and that this coupling breaks in very low metallicity objects.

Description: We present deep spectrophotometry of several H ii regions in the nearby low-mass spiral galaxies NGC 300 and M33. The data have been taken with Ultraviolet–Visual Echelle Spectrograph and Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy spectrographs attached to the 8-m Very Large Telescope and 10.4-m Gran Telescopio Canarias telescopes, respectively. We have derived precise values of the physical conditions for each object making use of several emission line-intensity ratios. In particular, we have obtained direct determinations of the electron temperature in all the observed objects. We detect pure recombination lines (RLs) of C ii and O ii in several of the H ii regions, permitting to derive their C/H and C/O ratios. We have derived the radial abundance gradient of O for each galaxy making use of collisionally excited lines (CELs) and RLs, as well as the C and N gradients using RLs and CELs, respectively. We obtain the first determination of the C/H gradient of NGC 300 and improve its determination in the case of M33. In both galaxies, the C/H gradients are steeper than those of O/H, leading to negative C/O gradients. Comparing with similar results for other spiral galaxies, we find a strong correlation between the slope of the C/H gradient and M V . We find that some H ii regions located close to the isophotal radius ( R 25 ) of NGC 300 and M33 show C/O ratios more similar to those typical of dwarf galaxies than those of H ii regions in the discs of more massive spirals. This may be related to the absence of flattening of the gradients in the external parts of NGC 300 and M33. Finally, we find very similar N/H gradients in both galaxies and a fair correlation between the slope of the N/H gradient and M V comparing with similar data for a sample of spiral galaxies.