ALBERT

Description: We present the first reported case of the simultaneous metallicity determination of a gamma-ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission-line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long-duration Swift GRB 121024A at z  = 2.30, we give one of the most complete views of a GRB host/environment to date. We observe a strong damped Lyα absorber (DLA) with a hydrogen column density of log  $N({\rm H\,{\small I}})\,=\,21.88\pm 0.10$ , H 2 absorption in the Lyman–Werner bands (molecular fraction of log( f ) –1.4; fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular emission lines Hα, Hβ, [O ii ], [O iii ] and [N ii ], as well as metal absorption lines. We find a GRB host galaxy that is highly star forming (SFR ~ 40 M  yr –1 ), with a dust-corrected metallicity along the line of sight of [Zn/H] corr  = –0.6 ± 0.2 ([O/H] ~ –0.3 from emission lines), and a depletion factor [Zn/Fe] = 0.85 ± 0.04. The molecular gas is separated by 400 km s –1 (and 1–3 kpc) from the gas that is photoexcited by the GRB. This implies a fairly massive host, in agreement with the derived stellar mass of log( M * /M ) =  $9.9^{+0.2}_{-0.3}$ . We dissect the host galaxy by characterizing its molecular component, the excited gas, and the line-emitting star-forming regions. The extinction curve for the line of sight is found to be unusually flat ( R V  ~ 15). We discuss the possibility of an anomalous grain size distributions. We furthermore discuss the different metallicity determinations from both absorption and emission lines, which gives consistent results for the line of sight to GRB 121024A.

Description: We present the first reported case of the simultaneous metallicity determination of a gamma-ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission-line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long-duration Swift GRB 121024A at z  = 2.30, we give one of the most complete views of a GRB host/environment to date. We observe a strong damped Lyα absorber (DLA) with a hydrogen column density of log  $N({\rm H\,{\small I}})\,=\,21.88\pm 0.10$ , H 2 absorption in the Lyman–Werner bands (molecular fraction of log( f ) –1.4; fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular emission lines Hα, Hβ, [O ii ], [O iii ] and [N ii ], as well as metal absorption lines. We find a GRB host galaxy that is highly star forming (SFR ~ 40 M  yr –1 ), with a dust-corrected metallicity along the line of sight of [Zn/H] corr  = –0.6 ± 0.2 ([O/H] ~ –0.3 from emission lines), and a depletion factor [Zn/Fe] = 0.85 ± 0.04. The molecular gas is separated by 400 km s –1 (and 1–3 kpc) from the gas that is photoexcited by the GRB. This implies a fairly massive host, in agreement with the derived stellar mass of log( M * /M ) =  $9.9^{+0.2}_{-0.3}$ . We dissect the host galaxy by characterizing its molecular component, the excited gas, and the line-emitting star-forming regions. The extinction curve for the line of sight is found to be unusually flat ( R V  ~ 15). We discuss the possibility of an anomalous grain size distributions. We furthermore discuss the different metallicity determinations from both absorption and emission lines, which gives consistent results for the line of sight to GRB 121024A.

Description: We present a detailed analysis of a red quasar at z = 2.32 with an intervening damped Lyman α absorber (DLA) at z = 2.13. Using high-quality data from the X-shooter spectrograph at ESO Very Large Telescope, we find that the absorber has a metallicity consistent with solar. We observe strong C i and H 2 absorption indicating a cold, dense absorbing medium. Partial coverage effects are observed in the C i lines, from which we infer a covering fraction of 27 ± 6 per cent and a physical diameter of the cloud of 0.1 pc. From the covering fraction and size, we estimate the size of the background quasar's broad line region. We search for emission from the DLA counterpart in optical and near-infrared imaging. No emission is observed in the optical data. However, we see tentative evidence for a counterpart in the H - and K '-band images. The DLA shows high depletion (as probed by [Fe/Zn] = –1.22) indicating that significant amounts of dust must be present in the DLA. By fitting the spectrum with various dust reddened quasar templates we find a best-fitting amount of dust in the DLA of A ( V ) DLA = 0.28 ± 0.01| stat ± 0.07| sys . We conclude that dust in the DLA is causing the colours of this intrinsically very luminous background quasar to appear much redder than average quasars, thereby not fulfilling the criteria for quasar identification in the Sloan Digital Sky Survey. Such chemically enriched and dusty absorbers are thus under-represented in current samples of DLAs.

Description: A scaling relation has recently been suggested to combine the galaxy mass–metallicity (MZ) relation with metallicities of damped Lyman α systems (DLAs) in quasar spectra. Based on this relation the stellar masses of the absorbing galaxies can be predicted. We test this prediction by measuring the stellar masses of 12 galaxies in confirmed DLA absorber–galaxy pairs in the redshift range 0.1 〈  z  〈 3.2. We find an excellent agreement between the predicted and measured stellar masses over three orders of magnitude, and we determine the average offset 〈 C [M/H] 〉 = 0.44 ± 0.10 between absorption and emission metallicities. We further test if C [M/H] could depend on the impact parameter and find a correlation at the 5.5 level. The impact parameter dependence of the metallicity corresponds to an average metallicity difference of –0.022 ± 0.004 dex kpc –1 . By including this metallicity versus impact parameter correlation in the prescription instead of C [M/H] , the scatter reduces to 0.39 dex in log M * . We provide a prescription on how to calculate the stellar mass ( $M_*^{\mathrm{DLA}}$ ) of the galaxy when both the DLA metallicity and DLA galaxy impact parameter is known. We demonstrate that DLA galaxies follow the MZ relation for luminosity-selected galaxies at z  = 0.7 and 2.2 when we include a correction for the correlation between impact parameter and metallicity.

Description: Gamma-ray burst (GRB) 111215A was bright at X-ray and radio frequencies, but not detected in the optical or near-infrared (nIR) down to deep limits. We have observed the GRB afterglow with the Westerbork Synthesis Radio Telescope and Arcminute Microkelvin Imager at radio frequencies, with the William Herschel Telescope and Nordic Optical Telescope in the nIR/optical, and with the Chandra X-ray Observatory . We have combined our data with the Swift X-Ray Telescope monitoring, and radio and millimetre observations from the literature to perform broad-band modelling, and determined the macro- and microphysical parameters of the GRB blast wave. By combining the broad-band modelling results with our nIR upper limits we have put constraints on the extinction in the host galaxy. This is consistent with the optical extinction we have derived from the excess X-ray absorption, and higher than in other dark bursts for which similar modelling work has been performed. We also present deep imaging of the host galaxy with the Keck I telescope, Spitzer Space Telescope , and Hubble Space Telescope ( HST ), which resulted in a well-constrained photometric redshift, giving credence to the tentative spectroscopic redshift we obtained with the Keck II telescope, and estimates for the stellar mass and star formation rate of the host. Finally, our high-resolution HST images of the host galaxy show that the GRB afterglow position is offset from the brightest regions of the host galaxy, in contrast to studies of optically bright GRBs.

Description: We present observations of three new sources in the European Southern Observatory VLT/X-shooter survey dedicated to the detection of the emitting counterparts of damped Lyα (DLA) systems towards bright quasars (QSOs). The aim is to bridge the observational gap between absorption (i.e. DLAs) and emission-selected galaxies at z ~ 2.2–2.5, in order to get a more complete picture of (proto)galaxies around this epoch. The hypothesis is that because DLA galaxies fulfil metallicity–velocity width and luminosity–metallicity relations, high-metallicity DLAs are more likely to be detected in emission. The region around each QSO is covered with slits (1.3 arcsec x 11 arcsec) at three different position angles. In the DLA towards QSO J205922.4–052842 ( z DLA  = 2.210, [S/H] = –0.91 ± 0.06), Lyα emission is detected at 3 confidence limit at an impact parameter of 〈6.3 kpc, and indicates a star formation rate 〉0.40 M yr –1 for the associated DLA galaxy. We do not detect the associated emission of two other DLAs in the spectra of QSOs J003034.4–512946 ( z DLA  = 2.452, [Zn/H] = –1.48 ± 0.34) and J105744.5+062914 ( z DLA  = 2.499, [Zn/H] = –0.24 ± 0.11, [S/H] = –0.15 ± 0.06). We conclude that focusing on metal-rich DLAs is a good way to find counterparts, but the non-detections at high metallicity (e.g. that of the DLA in J105744.5+062914) show that there is not a one-to-one relationship, and cautions us to not naively apply the properties of the DLA counterparts to all metal-rich DLAs.

Description: We present the results of a new search for bright star-forming galaxies at redshift $z$ ~= 7 within the UltraVISTA second data release (DR2) and UKIDSS (UKIRT Infrared Deep Sky Survey) UDS (Ultra Deep Survey) DR10 data, which together provide 1.65 deg 2 of near-infrared imaging with overlapping optical and Spitzer data. Using a full photometric redshift analysis, to identify high-redshift galaxies and reject contaminants, we have selected a sample of 34 luminous ($-22.7〈M_{\text{UV}}〈-21.2$) galaxies with 6.5 〈 $z$ 〈 7.5. Crucially, the deeper imaging provided by UltraVISTA DR2 confirms all of the robust objects previously uncovered by Bowler et al., validating our selection technique. Our new expanded galaxy sample includes the most massive galaxies known at $z$ ~= 7, with M *  ~= 10 10 M , and the majority are resolved, consistent with larger sizes ( r 1/2  ~= 1–1.5 kpc) than displayed by less massive galaxies. From our final robust sample, we determine the form of the bright end of the rest-frame UV galaxy luminosity function (LF) at $z$ ~= 7, providing strong evidence that it does not decline as steeply as predicted by the Schechter-function fit to fainter data. We exclude the possibility that this is due to either gravitational lensing, or significant contamination of our galaxy sample by active galactic nuclei (AGN). Rather, our results favour a double power-law form for the galaxy LF at high redshift, or, more interestingly, an LF which simply follows the form of the dark matter halo mass function at bright magnitudes. This suggests that the physical mechanism which inhibits star formation activity in massive galaxies (i.e. AGN feedback or some other form of ‘mass quenching’) has yet to impact on the observable galaxy LF at $z$ ~= 7, a conclusion supported by the estimated masses of our brightest galaxies which have only just reached a mass comparable to the critical ‘quenching mass’ of M *  ~= 10 10.2 M derived from studies of the mass function of star-forming galaxies at lower redshift.

Description: We analyse a sample of 16 absorption systems intrinsic to long-duration gamma-ray burst (GRB) host galaxies at z   2 for which the metallicities are known. We compare the relation between the metallicity and cold gas velocity width for this sample to that of the QSO-DLAs (quasi-stellar object–damped Lyman α), and find complete agreement. We then compare the redshift evolution of the mass–metallicity relation of our sample to that of QSO-DLAs and find that also GRB hosts favour a late onset of this evolution, around a redshift of 2.6. We compute predicted stellar masses for the GRB host galaxies using the prescription determined from QSO-DLA samples and compare the measured stellar masses for the four hosts where stellar masses have been determined from spectral energy distribution (SED) fits. We find excellent agreement and conclude that, on basis of all available data and tests, long-duration GRB-DLA hosts and intervening QSO-DLAs are consistent with being drawn from the same underlying population. GRB host galaxies and QSO-DLAs are found to have different impact parameter distributions and we briefly discuss how this may affect statistical samples. The impact parameter distribution has two effects. First, any metallicity gradient will shift the measured metallicity away from the metallicity in the centre of the galaxy, and secondly, the path of the sightline through different parts of the potential well of the dark matter halo will cause different velocity fields to be sampled. We report evidence suggesting that this second effect may have been detected.

Description: We present the extensive follow-up campaign on the afterglow of GRB 110715A at 17 different wavelengths, from X-ray to radio bands, starting 81 s after the burst and extending up to 74 d later. We performed for the first time a GRB afterglow observation with the ALMA observatory. We find that the afterglow of GRB 110715A is very bright at optical and radio wavelengths. We use the optical and near-infrared spectroscopy to provide further information about the progenitor's environment and its host galaxy. The spectrum shows weak absorption features at a redshift z = 0.8225, which reveal a host-galaxy environment with low ionization, column density, and dynamical activity. Late deep imaging shows a very faint galaxy, consistent with the spectroscopic results. The broad-band afterglow emission is modelled with synchrotron radiation using a numerical algorithm and we determine the best-fitting parameters using Bayesian inference in order to constrain the physical parameters of the jet and the medium in which the relativistic shock propagates. We fitted our data with a variety of models, including different density profiles and energy injections. Although the general behaviour can be roughly described by these models, none of them are able to fully explain all data points simultaneously. GRB 110715A shows the complexity of reproducing extensive multiwavelength broad-band afterglow observations, and the need of good sampling in wavelength and time and more complex models to accurately constrain the physics of GRB afterglows.

Description: The quasar Q0918+1636 ( z = 3.07) has an intervening high-metallicity damped Lyman α absorber (DLA) along the line of sight, at a redshift of z = 2.58. The DLA is located at a large impact parameter of 16.2 kpc, and despite this large impact parameter, it has a very high metallicity (consistent with solar). In this paper, it is investigated whether a novel type of galaxy formation models, based on hydrodynamical/gravitational TreeSPH simulations invoking a new Supernova Type II feedback prescription, the Haardt & Madau most recent ultraviolet background radiation (UVB) field and explicit treatment of UVB self-shielding effects, can reproduce the observed characteristics of the DLA. Effects of UV radiation from young stellar populations in the galaxy, in particular in the photon energy range 10.36–13.61 eV (relating to Sulphur II abundance), are also considered in the analysis. It is found that (a) for L ~ L * galaxies (at z = 2.58), about 10 per cent of the sight-lines through the galaxies at impact parameter b = 16.2 kpc will display a Sulphur II column density of $N(\rm {S\,\small {II})} \ge 10^{15.82}$ cm –2 (the observed value for the DLA), and (b) considering only cases where a near-solar metallicity will be detected at 16.2 kpc impact parameter, the (Bayesian) probability distribution of galaxy star formation rate peaks near the value observed for the DLA galaxy counterpart of $27^{+20}_{-9} {\,\mathrm{M}_{\odot }}$  yr –1 . It is argued that the bulk of the α-elements, like Sulphur, traced by the high metal column density, b = 16.2 kpc absorption lines, have been produced by evolving stars in the inner galaxy, and subsequently transported outwards by galactic winds.