Search

The existence of a secondary (in addition to compact object mergers) source of heavy element ( r -process) nucleosynthesis, the core-collapse of rapidly rotating and highly magnetized massive stars, has been suggested by both simulations and indirect observational evidence. Here, we probe a predicted signature of r -process enrichment, a late-time (≳40 days post-burst) distinct red color, in observations of gamma-ray burst supernovae (GRB-SNe), which are linked to these massive star progenitors. We present optical to near-IR color measurements of four GRB-SNe at z ≲ 0.4, extending out to >500 days post-burst, obtained with the Hubble Space Telescope and large-aperture ground-based telescopes. Comparison of our observations to models indicates that GRBs 030329, 100316D, and 130427A are consistent with both no enrichment and producing 0.01–0.15 M _⊙ of r -process material if there is a low amount of mixing between the inner r -process ejecta and outer supernova (SN) layers. GRB 190829A is not consistent with any models with r -process enrichment ≥0.01 M _⊙ . Taken together the sample of GRB-SNe indicates color diversity at late times. Our derived yields from GRB-SNe may be underestimated due to r -process material hidden in the SN ejecta (potentially due to low mixing fractions) or the limits of current models in measuring r -process mass. We conclude with recommendations for future search strategies to observe and probe the full distribution of r -process produced by GRB-SNe.

In this work we used a sample of 20 variable active galactic nuclei at 0.3 < z < 0.8 from the Ultra-VISTA survey to test whether their emission in the near-infrared (NIR) is consistent with emission from the dusty torus or the accretion disc, and whether the radius–luminosity relation found for local sources, is also seen when we consider sources from our sample. We carried out a spectral energy distribution analysis and conclude that 14 of the 20 sources have a variable component dominated by the dusty torus, and four have a variable component dominated by the accretion disc and two sources give uncertain results. Correcting for the disc contamination in the observed-frame Ks band, however, allowed us to determine dust lags for 13 sources after performing cross-correlation analysis. Special care was taken to consider lags that were not biased by seasonal gaps. Our determined lags are systematically found below the radius–luminosity relationship determined for local sources. Following previous works, we introduce an empirical relation that corrects lags by the rest-frame wavelength of the band that samples the dust emission, as shorter wavelengths arise from hotter regions of the torus. When the correction is introduced, our results are consistent with previous findings. We finally discuss whether other intrinsic parameters might also contribute to this effect and how these corrections will impact future large optical and NIR surveys. [ABSTRACT FROM AUTHOR]

Author(s): The LIGO Scientific Collaboration and The Virgo Collaboration; B. P. Abbott [1]; R. Abbott [1]; T. D. Abbott [2]; F. Acernese [3, 4]; K. Ackley [5, 6]; C. Adams [...]

We reduce and analyse the available JWST ERO and ERS NIRCam imaging (SMACS0723, GLASS, CEERS) in combination with the latest deep ground-based near-infrared imaging in the COSMOS field (provided by UltraVISTA DR5) to produce a new measurement of the evolving galaxy UV luminosity function (LF) over the redshift range z  = 8 − 15. This yields a new estimate of the evolution of UV luminosity density (ρUV), and hence cosmic star formation rate density (ρSFR) out to within <300 Myr of the Big Bang. Our results confirm that the high-redshift LF is best described by a double power law (rather than a Schechter) function up to z ∼ 10, and that the LF and the resulting derived ρUV (and thus ρSFR), continues to decline gradually and steadily up to z ∼ 15 (as anticipated from previous studies which analysed the pre-existing data in a consistent manner to this study). We provide details of the 61 high-redshift galaxy candidates, 47 of which are new, that have enabled this new analysis. Our sample contains 6 galaxies at z ≥ 12, one of which appears to set a new redshift record as an apparently robust galaxy candidate at z ≃ 16.4, the properties of which we therefore consider in detail. The advances presented here emphasize the importance of achieving high dynamic range in studies of early galaxy evolution, and re-affirm the enormous potential of forthcoming larger JWST programmes to transform our understanding of the young Universe. [ABSTRACT FROM AUTHOR]

We present a first-look analysis of the JWST ERO data in the SMACS J0723.3-7327 cluster field. We begin by reporting 10 new spectroscopic redshifts from λobs = 1.8–5.2 μm NIRSpec medium-resolution (R  = λ/Δλ = 1000) data. These are determined via multiple high-SNR emission line detections with five objects at 1 < z < 3 displaying multiple rest-frame near-infrared Hydrogen Paschen lines, and five objects at 5 < z < 9 displaying rest-frame optical Oxygen and Hydrogen Balmer lines. For the five higher-redshift galaxies we extract fluxes in six NIRCam bands spanning λobs = 0.8–5 μm and perform spectral energy distribution fitting in combination with existing HST photometry. The 7 < z < 9 objects exhibit a U-shaped pattern across the F 277 W, F 356 W , and F 444 W bands, indicating a Balmer break seen in emission (Balmer jump) and high-equivalent-width [O  iii ] emission. This indicates an extremely young stellar population with the bulk of the current mass having formed within the past 10 Myr. We report robust stellar masses and mean stellar ages from our spectral fitting with the four z > 6 galaxies exhibiting low-stellar masses from log10 (M */M⊙) = 7.1–8.2, and correspondingly young mean stellar ages of only a few Myr. This work highlights the critical importance of combining large upcoming NIRCam surveys with NIRSpec follow-up to measure the spectroscopic redshifts necessary to robustly constrain physical parameters. [ABSTRACT FROM AUTHOR]

We utilize deep near-infrared survey data from the UltraVISTA fourth data release (DR4) and the VIDEO survey, in combination with overlapping optical and  Spitzer data, to search for bright star-forming galaxies at z ≳ 7.5. Using a full photometric redshift fitting analysis applied to the ∼6 |$\, {\rm deg}^2$|  of imaging searched, we find 27 Lyman break galaxies (LBGs), including 20 new sources, with best-fitting photometric redshifts in the range 7.4 < z < 9.1. From this sample, we derive the rest-frame UV luminosity function at z = 8 and z = 9 out to extremely bright UV magnitudes (M UV ≃ −23) for the first time. We find an excess in the number density of bright galaxies in comparison to the typically assumed Schechter functional form derived from fainter samples. Combined with previous studies at lower redshift, our results show that there is little evolution in the number density of very bright (M UV ∼ −23) LBGs between z ≃ 5 and z ≃ 9. The tentative detection of an LBG with best-fitting photometric redshift of z = 10.9 ± 1.0 in our data is consistent with the derived evolution. We show that a double power-law fit with a brightening characteristic magnitude (Δ M */Δ z ≃ −0.5) and a steadily steepening bright-end slope (Δβ/Δ z ≃ −0.5) provides a good description of the z > 5 data over a wide range in absolute UV magnitude (−23 < M UV < −17). We postulate that the observed evolution can be explained by a lack of mass quenching at very high redshifts in combination with increasing dust obscuration within the first |${\sim}1 \, {\rm Gyr}$| of galaxy evolution. [ABSTRACT FROM AUTHOR]

With a total integration time of 168 h and a narrowband filter tuned to Lyα emission from z = 8.8, the UltraVISTA survey has set out to find some of the most distant galaxies, on the verge of the epoch of reionization. Previous calculations of the expected number of detected Lyα-emitting galaxies (LAEs) at this redshift based for example on extrapolation of lower-redshift luminosity functions did not explicitly take into account the radiative transfer of Lyα. In this work we have combined a theoretical model for the halo mass function, that is, the expected number of haloes per volume, with numerical results from high-resolution cosmological hydro-simulations post-processed with radiative transfer of ionizing UV and Lyα radiation, assessing the visibility of LAEs residing in these haloes. We have taken into account uncertainties such as cosmic variance and the anisotropic escape of Lyα, and predict that once the survey has finished, the probabilities of detecting none, one, or more than one are roughly 90%, 10%, and 1%, respectively. This is a significantly smaller success rate than in earlier predictions, due to the combined effect of a highly neutral intergalactic medium (IGM) scattering Lyα to such large distances from the galaxy that they fall outside the observational aperture, and to the actual depth of the survey being less than predicted. Because the IGM affects narrowband (NB) and broadband (BB) magnitudes differently, we argue for a relaxed colour selection criterion of mNB − mBB ≃ +0.85 in the AB system. Since the flux is dominated by the continuum, however, even if a galaxy is detectable in the NB, its probability of being selected as a narrowband excess object is ≲35%. Various additional properties of galaxies at this redshift are predicted, for example, the Lyα and UV luminosity functions, the stellar mass–halo mass relation, the spectral shape, the optimal aperture, as well as the anisotropic escape of Lyα through both the dusty, interstellar medium and through the partly neutral IGM. Finally, we describe and make public a fast numerical code for adding numbers with asymmetric uncertainties (" x+σ+−σ− x − σ − + σ + $ x_{-\sigma_{-}}^{+\sigma_{+}} $ ") which proves significantly more precise than the standard, but wrong, way of separately adding upper and lower uncertainties in quadrature. [ABSTRACT FROM AUTHOR]

We explore the possible effect of cluster environments on the structure and star formation histories of galaxies by analysing the projected phase–space (PPS) of intermediate-redshift clusters (0.4 ≤ z ≤ 0.8). HST I −band imaging data from the ESO Distant Cluster Survey (EDisCS) allow us to measure deviations of the galaxies' light distributions from symmetric and smooth profiles using two parameters, A res ('asymmetry') and RFF (residual flux fraction or 'roughness'). Combining these structural parameters with age-sensitive spectral indicators (⁠|$H_{\delta \rm {A}}$|⁠, |$H_{\gamma \rm {A}}$|⁠, and Dn 4000), we establish that in all environments younger star-forming galaxies of all morphologies are 'rougher' and more asymmetric than older, more quiescent ones. Combining a subset of the EDisCS clusters, we construct a stacked PPS diagram and find a significant correlation between the position of the galaxies on the PPS and their stellar ages, irrespective of their morphology. We also observe an increasing fraction of galaxies with older stellar populations towards the cluster core, while the galaxies' structural parameters (A res and RFF) do not seem to segregate strongly with PPS. These results may imply that, under the possible influence of their immediate cluster environment, galaxies have their star formation suppressed earlier, while their structural transformation happens on a longer time-scale as they accumulate and age in the cluster cores. [ABSTRACT FROM AUTHOR]

Damped Lyman-α absorbers (DLAs) as a class of quasi-stellar object (QSO) absorption-line systems are currently our most important source of detailed information on the cosmic chemical evolution of galaxies. However, the degree to which this information is biased by dust remains to be understood. One strategy is to specifically search for QSOs that are reddened by metal-rich and dusty foreground absorbers. In this Letter, we present the discovery of a z = 2.60 QSO that is strongly reddened by dust in an intervening extremely strong DLA at z = 2.226. This QSO was identified through a novel selection that combined the astrometric measurements from ESA's Gaia satellite with extisting optical and near- to mid-infrared photometry. We infer a total neutral atomic-hydrogen column density of log N(H I) = 21.95 ± 0.15 and a lower limit on the gas-phase metallicity of [Zn/H] >  −0.96. This DLA is also remarkable in that it exhibits shielded neutral gas that is visible in C I, and it shows tentative detections of CO molecular bands. The spectral energy distribution of the QSO is well accounted for by a spectral energy distribution that is normal for a QSO and is reddened by dust from a DLA with 10% solar metallicity, a dust extinction of AV = 0.82 ± 0.02 mag, and an extinction curve that resembles that of the Large Magellanic Cloud, including the characteristic 2175 Å extinction feature. Such QSO absorption-line systems have been shown to be very rare in previous surveys, which have mostly revealed sight-lines with low extinction. The present case therefore suggests that previous samples have under-represented the fraction of dusty absorbers. Building a complete sample of such systems is required to assess the significance of this effect. [ABSTRACT FROM AUTHOR]

Whether stars could have driven the reionization of the intergalactic medium depends critically on the proportion of ionizing radiation that escapes the galaxies in which it is produced. Spectroscopy of gamma-ray burst (GRB) afterglows can be used to estimate the opacity to extreme ultraviolet (EUV) radiation along the lines-of-sight to the bursts. Assuming that long-duration GRBs trace the locations of the massive stars dominating EUV production, the average escape fraction of ionizing radiation can be calculated independently of galaxy size or luminosity. Here we present a compilation of H  i column density (⁠|${N_{\rm {\small H\,I}}}$|⁠) measures for 140 GRBs in the range 1.6 < |$z$| < 6.7. Although the sample is heterogeneous, in terms of spectral resolution and signal-to-noise ratio, fits to the Ly α absorption line provide robust constraints on |${N_{\rm {\small H\,I}}}$|⁠, even for spectra of insufficient quality for other purposes. Thus we establish an escape fraction at the Lyman limit of 〈 f esc〉 ≈ 0.005, with a 98 per cent confidence upper limit of 〈 f esc〉 ≈ 0.015. This analysis suggests that stars provide a small contribution to the ionizing radiation budget at |$z$| < 5. At higher redshifts firm conclusions are limited by the small size of the GRB sample (7/140), but any decline in average H  i column density seems to be modest. We also find no significant correlation of |${N_{\rm {\small H\,I}}}$| with galaxy UV luminosity or host stellar mass. We discuss in some detail potential biases and argue that, while not negligible, systematic errors in f esc are unlikely to be more than a factor ∼2 in either direction, and so would not affect the primary conclusions. Given that many GRB hosts are low-metallicity dwarf galaxies with high specific star-formation rates, these results present a particular problem for the hypothesis that such galaxies dominated the reionization of the Universe. [ABSTRACT FROM AUTHOR]

It is notoriously difficult to localize short γ-ray bursts (sGRBs) and their hosts to measure their redshifts. These measurements, however, are critical for constraining the nature of sGRB progenitors, their redshift distribution, and the r-process element enrichment history of the universe. Here we present spectroscopy of the host galaxy of GRB 111117A and measure its redshift to be z = 2.211. This makes GRB 111117A the most distant high-confidence short duration GRB detected to date. Our spectroscopic redshift supersedes a lower, previously estimated photometric redshift value for this burst. We use the spectroscopic redshift, as well as new imaging data to constrain the nature of the host galaxy and the physical parameters of the GRB. The rest-frame X-ray derived hydrogen column density, for example, is the highest compared to a complete sample of sGRBs and seems to follow the evolution with redshift as traced by the hosts of long GRBs. From the detection of Lyα emission in the spectrum, we are able to constrain the escape fraction of Lyα in the host. The host lies in the brighter end of the expected sGRB host brightness distribution at z = 2.211, and is actively forming stars. Using the observed sGRB host luminosity distribution, we find that between 43% and 71% of all Swift-detected sGRBs have hosts that are too faint at z ~ 2 to allow for a secure redshift determination. This implies that the measured sGRB redshift distribution could be incomplete at high redshift. The high z of GRB 111117A is evidence against a lognormal delay-time model for sGRBs through the predicted redshift distribution of sGRBs, which is very sensitive to high-z sGRBs. From the age of the universe at the time of GRB explosion, an initial neutron star (NS) separation of a0 < 3.1 R⊙ is required in the case where the progenitor system is a circular pair of inspiralling NSs. This constraint excludes some of the longest sGRB formation channels for this burst. [ABSTRACT FROM AUTHOR]

We here present the spectroscopic follow-up observations with VLT/X-shooter of the Swift long-duration gamma-ray burst GRB160804A at ɀ=0.737. Typically, GRBs are found in lowmass, metal-poor galaxies that constitute the sub-luminous population of star-forming galaxies. For the host galaxy of the GRB presented here, we derive a stellar mass of log (M*/M⨀) = 9.80 ± 0.07, a roughly solar metallicity (12 + log (O/H) = 8.74 ± 0.12) based on emission line diagnostics, and an infrared luminosity of M3.6/(1 + ɀ) = -21.94 mag, but find it to be dust-poor (E(B -- V) < 0.05 mag). This establishes the galaxy hosting GRB160804A as one of the most luminous, massive and metal-rich GRB hosts at ɀ < 1.5. Furthermore, the gasphase metallicity is found to be representative of the physical conditions of the gas close to the explosion site of the burst. The high metallicity of the host galaxy is also observed in absorption, where we detect several strong Fe II transitions as well as MgII and MgI. Although host galaxy absorption features are common in GRB afterglow spectra, we detect absorption from strong metal lines directly in the host continuum (at a time when the afterglow was contributing to <15 per cent). Finally, we discuss the possibility that the geometry and state of the absorbing and emitting gas are indicative of a galactic scale outflow expelled at the final stage of two merging galaxies. [ABSTRACT FROM AUTHOR]

Since the first discovery of a broad-lined type Ic supernova (SN) with a long-duration gamma-ray burst (GRB) in 1998, fewer than fifty GRB-supernovae (SNe) have been discovered. The intermediate-luminosity Swift GRB 161219B and its associated supernova SN 2016jca, which occurred at a redshift of z = 0.1475, represents only the seventh GRB-SN to have been discovered within 1 Gpc, and hence provides an excellent opportunity to investigate the observational and physical properties of these very elusive and rare type of SN. As such, we present optical to near-infrared photometry and optical spectroscopy of GRB 161219B and SN 2016jca, spanning the first three months since its discovery. GRB 161219B exploded in the disk of an edge-on spiral galaxy at a projected distance of 3.4 kpc from the galactic centre. GRB 161219B itself is an outlier in the Ep;i - Eγ;iso plane, while SN 2016jca had a rest-frame, peak absolute V-band magnitude of MV = -19.0 ± 0.1, which it reached after 12.3 ± 0.7 rest-frame days. We find that the bolometric properties of SN 2016jca are inconsistent with being powered solely by a magnetar central engine, and demonstrate that it was likely powered exclusively by energy deposited by the radioactive decay of nickel and cobalt into their daughter products, which were nucleosynthesised when its progenitor underwent core collapse. We find that 0.22 ± 0.08 M☉ of nickel is required to reproduce the peak luminosity of SN 2016jca, and we constrain an ejecta mass of 5.8 ± 0.3 M☉ and a kinetic energy of 5.1 ± 0.8 × 1052 erg. Finally, we report on a chromatic, pre-maximum bump in the g-band light curve, and discuss its possible origin. [ABSTRACT FROM AUTHOR]

With the aim of understanding the effect of the environment on the star formation history and morphological transformation of galaxies, we present a detailed analysis of the colour, morphology and internal structure of cluster and field galaxies at 0.4 ≤ z ≤ 0.8. We use the Hubble Space Telescope data for over 500 galaxies from the ESO Distant Cluster Survey to quantify how the galaxies' light distribution deviate from symmetric smooth profiles. We visually inspect the galaxies' images to identify the likely causes for such deviations. We find that the residual flux fraction (RFF), which measures the fractional contribution to the galaxy light of the residuals left after subtracting a symmetric and smooth model, is very sensitive to the degree of structural disturbance but not the causes of such disturbance. On the other hand, the asymmetry of these residuals (Ares) is more sensitive to the causes of the disturbance, with merging galaxies having the highest values of Ares. Using these quantitative parameters, we find that, at a fixed morphology, cluster and field galaxies show statistically similar degrees of disturbance. However, there is a higher fraction of symmetric and passive spirals in the cluster than in the field. These galaxies have smoother light distributions than their star-forming counterparts. We also find that while almost all field and cluster S0s appear undisturbed, there is a relatively small population of star-forming S0s in clusters but not in the field. These findings are consistent with relatively gentle environmental processes acting on galaxies infalling on to clusters. [ABSTRACT FROM AUTHOR]

The sub-population of quasars reddened by intrinsic or intervening clouds of dust are known to be underrepresented in optical quasar surveys. By defining a complete parent sample of the brightest and spatially unresolved quasars in the COSMOS field, we quantify to which extent this sub-population is fundamental to our understanding of the true population of quasars. By using the available multiwavelength data of various surveys in the COSMOS field, we built a parent sample of 33 quasars brighter than J = 20 mag, identified by reliable X-ray to radio wavelength selection techniques. Spectroscopic follow-up with the NOT/ALFOSC was carried out for four candidate quasars that had not been targeted previously to obtain a 100% redshift completeness of the sample. The population of high AV quasars (HAQs), a specific sub-population of quasars selected from optical/near-infrared photometry, some of which were shown to be missed in large optical surveys such as SDSS, is found to contribute 21%-5+9 of the parent sample. The full population of bright spatially unresolved quasars represented by our parent sample consists of 39%-8+9 reddened quasars defined by having AV > 0:1, and 21%-5+9 of the sample having E(B-V) > 0:1 assuming the extinction curve of the Small Magellanic Cloud. We show that the HAQ selection works well for selecting reddened quasars, but some are missed because their optical spectra are too blue to pass the g - r color cut in the HAQ selection. This is either due to a low degree of dust reddening or anomalous spectra. We find that the fraction of quasars with contributing light from the host galaxy, causing observed extended spatial morphology, is most dominant at z ≲ 1. At higher redshifts the population of spatially unresolved quasars selected by our parent sample is found to be representative of the full population of bright active galactic nuclei at J < 20 mag. This work quantifies the bias against reddened quasars in studies that are based solely on optical surveys. [ABSTRACT FROM AUTHOR]

Context. High redshift star-forming galaxies are discovered routinely because of a flux excess in narrowband filters caused by an emission line. In most cases, the width of such filters is broader than typical line widths, and the throughput of the filters varies substantially within the bandpass. This leads to substantial uncertainties in redshifts and fluxes that are derived from the observations with one specific narrowband filter. Aims. The uncertainty in measured line parameters can be sharply reduced by using repeated observations of the same target field with filters that have overlapping passbands but differ slightly in central wavelength or wavelength dependence of the effective filter curve. Such data are routinely collected with some large field imaging cameras that use multiple detectors and a separate filter for each of the detectors. An example is the European Southern Observatory’s VISTA InfraRed CAMera (VIRCAM). Methods. We developed a method of determining more accurate redshift and line flux estimates from the ratio of apparent fluxes measured from observations in different narrowband filters and several matching broadband filters. A parameterized model of the line and continuum flux is used to predict the flux ratios as a function of redshift based on the known filter curves. These model predictions are then used to determine the most likely redshift and line flux. Results. We tested the obtainable quality of parameter estimation for the example of Hα in the VIRCAM NB118 filters both on simulated and actual observations where the latter were based on the UltraVISTA DR2 data set. We combined the narrowband data with deep broadband data in Y, J, and H. We find that with this method, the errors in the measured lines fluxes can be reduced up to almost an order of magnitude. Conclusions. We conclude that existing narrowband data can be used to derive accurate line fluxes if the observations include images taken with sufficiently different filter curves. For the UltraVISTA survey, the best-suited narrowband filter combinations allow an accuracy in wavelength of better than 1 nm and in flux of better than 15% at any redshift within the bandpass of the filters. In contrast, analyzing the data without exploiting the difference in filter curves leads to an uncertainty in wavelength of 10 nm and up to an order of magnitude errors in line flux estimates. [ABSTRACT FROM AUTHOR]

We present the results of a search for bright (-22.7 ≤ MUV ≤ -20.5) Lyman-break galaxies at z ≃ 6 within a total of 1.65 deg² of imaging in the UltraVISTA/Cosmological Evolution Survey (COSMOS) and United Kingdom Infrared Telescope Deep Sky Survey (UKIDSS) Ultra Deep Survey (UDS) fields. The deep near-infrared imaging available in the two independent fields, in addition to deep optical (including z'-band) data, enables the sample of z ≃ 6 star-forming galaxies to be securely detected longward of the break (in contrast to several previous studies). We show that the expected contamination rate of our initial sample by cool Galactic brown dwarfs is ≲3 per cent and demonstrate that they can be effectively removed by fitting brown dwarf spectral templates to the photometry. At z ≃ 6, the galaxy surface density in the UltraVISTA field exceeds that in the UDS by a factor of ≃ 1.8, indicating strong cosmic variance even between degree-scale fields at z > 5. We calculate the bright end of the rest-frame Ultraviolet (UV) luminosity function (LF) at z ≃ 6. The galaxy number counts are a factor of ~1.7 lower than predicted by the recent LF determination by Bouwens et al. In comparison to other smaller area studies, we find an evolution in the characteristic magnitude between z ≃ 5 and z ≃ 7 of ΔM* ~ 0.4, and show that a double power law or a Schechter function can equally well describe the LF at z = 6. Furthermore, the bright end of the LF appears to steepen from z ≃ 7 to z ≃ 5, which could indicate the onset of mass quenching or the rise of dust obscuration, a conclusion supported by comparing the observed LFs to a range of theoretical model predictions. [ABSTRACT FROM AUTHOR]

We have obtained deep NIR narrow and broad (J and Y) band imaging data of the GOODS-South field. The narrow band filter is centered at 1060 nm corresponding to redshifts z = 0.62, 1.15, 1.85 for the strong emission lines Hα, [Oiii]/Hβ and [Oii], respectively. From those data we extract a well defined sample (M(AB) = 24.8 in the narrow band) of objects with large emission line equivalent widths in the narrow band. Via SED fits to published broad band data we identify which of the three lines we have detected and assign redshifts accordingly. This results in a well defined, strong emission line selected sample of galaxies down to lower masses than can easily be obtained with only continuum flux limited selection techniques. We compare the (SED fitting-derived) main sequence of star-formation (MS) of our sample to previous works and find that it has a steeper slope than that of samples of more massive galaxies. We conclude that the MS steepens at lower (below M⨰= 109.4 M☉) galaxy masses. We also show that the SFR at any redshift is higherin our sample. We attribute this to the targeted selection of galaxies with large emission line equivalent widths, and conclude that our sample forms the upper boundary of the MS. We briefly investigate and outline how samples with accurate redshifts down to those low stellar masses open a new window to study the formation of large scale structure in the early universe. In particular we report on the detection of a young galaxy cluster at z = 1.85 which features a central massive galaxy which is the candidate of an early stage cD galaxy, and we identify a likely filament mapped out by [Oiii] and Hβ emitting galaxies at z = 1.15. [ABSTRACT FROM AUTHOR]

Context. The reionisation of the Universe is a process that is thought to have ended around z ~ 6, as inferred from spectroscopy of distant bright background sources, such as quasars (QSO) and gamma-ray burst (GRB) afterglows. Furthermore, spectroscopy of a GRB afterglow provides insight in its host galaxy, which is often too dim and distant to study otherwise. Aims. For the Swift GRB130606A at z = 5.913 we have obtained a high S/N spectrum covering the full optical and near-IR wavelength region at intermediate spectral resolution with VLT/X-Shooter. We aim to measure the degree of ionisation of the intergalactic medium (IGM) between z = 5.02-5.84 and to study the chemical abundance pattern and dust content of its host galaxy. Methods. We estimated the UV continuum of the GRB afterglow using a power-law extrapolation, then measured the flux decrement due to absorption at Lyα, β, and γ wavelength regions. Furthermore, we fitted the shape of the red damping wing of Lyα. The hydrogen and metal absorption lines formed in the host galaxy were fitted with Voigt profiles to obtain column densities. We investigated whether ionisation corrections needed to be applied. Results. Our measurements of the Lyα-forest optical depth are consistent with previous measurements of QSOs, but have a much smaller uncertainty. The analysis of the red damping wing yields a neutral fraction xHi < 0.05 (3σ). We obtain column density measurements of H, Al, Si, and Fe; for C, O, S and Ni we obtain limits. The ionisation due to the GRB is estimated to be negligible (corrections <0.03 dex), but larger corrections may apply due to the pre-existing radiation field (up to 0.4 dex based on sub-DLA studies). Assuming that [Si/Fe] = +0.79 ± 0.13 is due to dust depletion, the dust-to-metal ratio is similar to the Galactic value. Conclusions. Our measurements confirm that the Universe is already predominantly ionised over the redshift range probed in this work, but was slightly more neutral at z > 5.6. GRBs are useful probes of the ionisation state of the IGM in the early Universe, but because of internal scatter we need a larger statistical sample to draw robust conclusions. The high [Si/Fe] in the host can be due to dust depletion, α-element enhancement, or a combination of both. The very high value of [Al/Fe] = 2.40 ± 0.78 might be due to a proton capture process and is probably connected to the stellar population history. We estimate the host metallicity to be -1.7 < [M/H] < -0.9 (2%-13% of solar). [ABSTRACT FROM AUTHOR]

We use percent-level precision photometric redshifts in the UltraVISTA-DR1 near-infrared survey to investigate the changing relationship between galaxy stellar mass and the dark matter haloes hosting them to z ~ 2. We achieve this by measuring the clustering properties and abundances of a series of volume-limited galaxy samples selected by stellar mass and star formation activity. We interpret these results in the framework of a phenomenological halo model and numerical simulations. Our measurements span a uniquely large range in stellar mass and redshift and reach below the characteristic stellar mass to z ~ 2. Our results are: (1) at fixed redshift and scale, clustering amplitude depends monotonically on sample stellar mass threshold; (2) at fixed angular scale, the projected clustering amplitude decreases with redshift but the comoving correlation length remains constant; (3) characteristic halo masses and galaxy bias increase with increasing median stellar mass of the sample; (4) the slope of these relationships is modified in lower mass haloes; (5) concerning the passive galaxy population, characteristic halo masses are consistent with a simply less-abundant version of the full galaxy sample, but at lower redshifts the fraction of satellite galaxies in the passive population is very different from the full galaxy sample; (6) finally,we find that the ratio between the characteristic halo mass and median stellar mass at each redshift bin reaches a peak at log (Mh/M⊙) ~ 12.2 and the position of this peak remains constant out to z ~ 2. The behaviour of the full and passively evolving galaxy samples can be understood qualitatively by considering the slow evolution of the characteristic stellar mass in the redshift range probed by our survey. [ABSTRACT FROM AUTHOR]

We present deep spectroscopy of 17 very low mass (M⋆ ≃ 2.0 × 106–1.4 × 109 M⊙) and low luminosity (MUV ≃ −13.7 to −19.9) gravitationally lensed galaxies in the redshift range z ≃ 1.5-3.0. Deep rest-frame ultraviolet spectra reveal large equivalent width emission from numerous emission lines (N iv], O iii], C iv, Si iii], C iii]) which are rarely seen in individual spectra of more massive star-forming galaxies. C iii] is detected in 16 of 17 low-mass star-forming systems with rest-frame equivalent widths as large as 13.5 Å. Nebular C iv emission is present in the most extreme C iii] emitters, requiring an ionizing source capable of producing a substantial component of photons with energies in excess of 47.9 eV. Photoionization models support a picture whereby the large equivalent widths are driven by the increased electron temperature and enhanced ionizing output arising from metal-poor gas and stars (0.04–0.13 Z⊙), young stellar populations (6–50 Myr), and large ionization parameters (log U = −2.16 to −1.84). The young ages implied by the emission lines and continuum spectral energy distributions (SEDs) indicate that the extreme line emitters in our sample are in the midst of a significant upturn in their star formation activity. The low stellar masses, blue UV colours, and large specific star formation rates of our sample are similar to those of typical z ≳ 6 galaxies. Given the strong attenuation of Lyα in z ≳ 6 galaxies, we suggest that C iii] is likely to provide our best probe of early star-forming galaxies with ground-based spectrographs and one off the most efficient means of confirming z ≳ 10 galaxies with the James Webb Space Telescope. [ABSTRACT FROM AUTHOR]

We use integral field spectroscopy of 13 disc galaxies in the cluster AC114 at z ∼ 0.31 in an attempt to disentangle the physical processes responsible for the transformation of spiral galaxies in clusters. Our sample is selected to display a dominant young stellar population, as indicated by strong Hδ absorption lines in their integrated spectra. Most of our galaxies lack the [O ii]λ3727 emission line, and hence ongoing star formation. They therefore possess ‘k+a’ spectra, indicative of a recent truncation of star formation, possibly preceded by a starburst. Discy ‘k+a’ galaxies are a promising candidate for the intermediate stage of the transformation from star-forming spiral galaxies to passive S0s. Our observations allow us to study the spatial distributions and the kinematics of the different stellar populations within the galaxies. We used three different indicators to evaluate the presence of a young population: the equivalent width of Hδ, the luminosity-weighted fraction of A stars, and the fraction of the galaxy light attributable to simple stellar populations with ages between 0.5 and 1.5 Gyr. We find a mixture of behaviours, but are able to show that in most of the galaxies the last episode of star formation occurred in an extended disc, similar to preceding generations of stars, though somewhat more centrally concentrated. We thus exclude nuclear starbursts and violent gravitational interactions as causes of the star formation truncation. Gentler mechanisms, such as ram-pressure stripping or weak galaxy–galaxy interactions, appear to be responsible for ending star formation in these intermediate-redshift cluster disc galaxies. [ABSTRACT FROM AUTHOR]

Observations of the high redshift Universe through narrow-band filters have proven very successful in the last decade. The 4-m VISTA telescope, equipped with the wide-field camera VIRCAM, offers a major step forward in wide-field near-infrared imaging, and in order to utilise VISTA's large field-of-view and sensitivity, the Dark Cosmology Centre provided a set of 16 narrow-band filters for VIRCAM. These NB118 filters are centered at a wavelength near 1.19 μm in a region with few airglow emission lines. The filters allow the detection of Hα emitters at z = 0.8, Hβ and [O III] emitters at z ≈ 1.4, [O II] emitters at z = 2.2, and Lyα emitters at z = 8.8. Based on guaranteed time observations of the COSMOS field we here present a detailed description and characterization of the filters and their performance. In particular we provide sky-brightness levels and depths for each of the 16 detector/filter sets and find that some of the filters show signs of some red-leak. We identify a sample of 2 x 103 candidate emission-line objects in the data. Cross-correlating this sample with a large set of galaxies with known spectroscopic redshifts we determine the "in situ" passbands of the filters and find that they are shifted by about 3.5-4 nm (corresponding to 30% of the filter width) to the red compared to the expectation based on the laboratory measurements. Finally, we present an algorithm to mask out persistence in VIRCAM data. Scientific results extracted from the data will be presented separately. [ABSTRACT FROM AUTHOR]

We present the redshift results from a Very Large Telescope (VLT) program aimed at optimizing the legacy value of the Swift mission: to characterize a homogeneous, X-ray selected, sample of 69 GRB host galaxies. Fifteen new redshifts have been secured, resulting in a 77~0 (53/69) redshift completion, making the survey the most comprehensive in terms of redshift completeness of any sample to the full Swift depth, available to date. We present the cumulative redshift distribution and derive a conservative, yet small, associated uncertainty. We constrain the fraction of Swift GRBs at high redshift to a maximum of 14% (5%) for ζ > 6 (ζ > 7). The mean redshift of the host sample is assessed to be (ζ) ~ 2.2. Using this more complete sample, we confirm previous findings that the GRB rate at high redshift (ζ ~ 3) appears to be in excess of predictions based on assumptions that it should follow conventional determinations of the star formation history of the universe, combined with an estimate of its likely metallicity dependence. This suggests that either star formation at high redshifts has been significantly underestimated, for example due to a dominant contribution from faint, undetected galaxies, or that GRB production is enhanced in the conditions of early star formation, beyond those usually ascribed to lower metallicity. [ABSTRACT FROM AUTHOR]

Abundances of galaxies at redshifts z > 4 are difficult to obtain from damped Lyα (DLA) systems in the sightlines of quasars (QSOs) due to the Lyα forest blanketing and the low number of high-redshift QSOs known to date. Gamma-ray bursts (GRBs) with their higher luminosity are well suited to study galaxies out to the formation of the first stars at z > 10. The large wavelength coverage of the X-shooter spectrograph makes it an excellent tool to study the interstellar medium of high-redshift galaxies, in particular if the redshift is not known beforehand. In this paper, we determine the properties of a GRB host at z = 4.667 23 from absorption lines combined with X-ray and optical imaging data. This is one of the highest redshifts where a detailed analysis with medium-resolution data is possible. We measure a relatively high metallicity of [S/H] = −1.1 ± 0.2 for a galaxy at this redshift. Assuming ultraviolet pumping as origin for the fine-structure lines, the material observed is between 0.3 and 1.0 kpc from the GRB. The extinction determined by the spectral slope from X-rays to the infrared shows a moderate value of AV = 0.13 ± 0.05 mag and relative abundances point to a warm disc extinction pattern. Low- and high-ionization as well as fine-structure lines show a complicated kinematic structure probably pointing to a merger in progress. We also detect one intervening system at z = 2.18. GRB-DLAs have a shallower evolution of metallicity with redshift than QSO absorbers and no evolution in their H i column density or ionization fraction. GRB hosts at high redshifts seem to continue the trend of the metallicity–luminosity relation towards lower metallicities but the sample is still too small to draw a definite conclusion. While the detection of GRBs at z > 4 with current satellites is still difficult, they are very important for our understanding of the early epochs of star and galaxy formation. [ABSTRACT FROM AUTHOR]

ABSTRACT Strong gravitational lensing magnifies the flux from distant galaxies, allowing us to detect emission lines that would otherwise fall below the detection threshold for medium-resolution spectroscopy. Here we present the detection of temperature-sensitive oxygen emission lines from three galaxies at 2 ≲ z ≲ 3.5, which enables us to directly determine the oxygen abundances and thereby double the number of galaxies at z > 2 for which this has been possible. The three galaxies have ∼10 per cent solar oxygen abundances in agreement with strong emission-line diagnostics. Carbon and nitrogen ratios relative to oxygen are subsolar as expected for young metal-poor galaxies. Two of the galaxies are Lyman α (Lyα) emitters with rest-frame equivalent widths of 20 and 40 Å, respectively, and their high magnification factors allow us for the first time to gain insight into the physical characteristics of high-redshift Lyα emitters. Using constraints from the physical properties of the galaxies, we accurately reproduce their line profiles with radiative transfer models. The models show a relatively small outflow in agreement with the observed small velocity offsets between nebular emission and interstellar absorption lines. [ABSTRACT FROM AUTHOR]

ABSTRACT We present Very Large Telescope/X-shooter spectra of 13 galaxies in the redshift range 1 ≲ z ≲ 6, which are strongly lensed by massive galaxy clusters. Spectroscopic redshifts are measured for nine galaxies, while three sources have redshifts determined from continuum breaks in their spectra. The stellar masses of the galaxies span four orders of magnitude between 107 and 1011 M⊙ and have luminosities at 1500 Å rest frame between 0.004 and 9 L* after correcting for the magnification. This allows us to probe a variety of galaxy types from young, low-mass starburst galaxies to massive evolved galaxies. The lensed galaxies with stellar masses less than 1010 M⊙ have a large scatter compared to the fundamental relation between stellar mass, star formation rates and oxygen abundances. We provide a modified fit to the fundamental relation for low-mass, low-metallicity galaxies with a weaker dependence of the metallicity on either the star formation rate or stellar mass compared to low-redshift, high-mass and high-metallicity Sloan Digital Sky Survey galaxies. [ABSTRACT FROM AUTHOR]

Context. The extreme brightness of gamma-ray burst (GRB) afterglows and their simple spectral shape make them ideal beacons to study the interstellar medium of their host galaxies through absorption line spectroscopy at almost any redshift. Aims. We describe the distribution of rest-frame equivalent widths (EWs) of the most prominent absorption features in GRB afterglow spectra, providing the means to compare individual spectra to the sample and identify its peculiarities. Methods. Using 69 low-resolution GRB afterglow spectra, we conduct a study of the rest-frame EWs distribution of features with an average rest-frame EW larger than 0.5 Å. To compare an individual GRB with the sample, we develop EW diagrams as a graphical tool, and we give a catalogue with diagrams for the 69 spectra. We introduce a line strength parameter (LSP) that allows us to quantify the strength of the absorption features in a GRB spectrum as compared to the sample by a single number. Using the distributions of EWs of single-species features, we derive the distribution of their column densities by a curve of growth (CoG) fit. Results. We find correlations between the LSP and the extinction of the GRB, the UV brightness of the host galaxies and the neutral hydrogen column density. However, we see no significant evolution of the LSP with the redshift. There is a weak correlation between the ionisation of the absorbers and the energy of the GRB, indicating that, either the GRB event is responsible for part of the ionisation, or that galaxies with high-ionisation media produce more energetic GRBs. Spectral features in GRB spectra are, on average, 2.5 times stronger than those seen in QSO intervening damped Lyman-α (DLA) systems and slightly more ionised. In particular we find a larger excess in the EW of C IVλλ1549 relative to QSO DLAs, which could be related to an excess of Wolf-Rayet stars in the environments of GRBs. From the CoG fitting we obtain an average number of components in the absorption features of GRBs of 6.00-1.25+1.00. The most extreme ionisation ratios in our sample are found for GRBs with low neutral hydrogen column density, which could be related to ionisation by the GRB emission. [ABSTRACT FROM AUTHOR]

ABSTRACT We have exploited the new, deep, near-infrared UltraVISTA imaging of the Cosmological Evolution Survey (COSMOS) field, in tandem with deep optical and mid-infrared imaging, to conduct a new search for luminous galaxies at redshifts z ≃ 7. The year-one UltraVISTA data provide contiguous Y, J, H, Ks imaging over 1.5 deg2, reaching a 5σ detection limit of Y + J ≃ 25 (AB mag, 2-arcsec-diameter aperture). The central ≃1 deg2 of this imaging coincides with the final deep optical ( u*, g, r, i) data provided by the Canada-France-Hawaii Telescope (CFHT) Legacy Survey and new deep Subaru/Suprime-Cam z′-band imaging obtained specifically to enable full exploitation of UltraVISTA. It also lies within the Hubble Space Telescope ( HST) I814 band and Spitzer/Infrared Array Camera imaging obtained as part of the COSMOS survey. We have utilized this unique multiwavelength dataset to select galaxy candidates at redshifts z > 6.5 by searching first for Y + J-detected objects which are undetected in the CFHT and HST optical data. This sample was then refined using a photometric redshift fitting code, enabling the rejection of lower redshift galaxy contaminants and cool galactic M, L, T dwarf stars. The final result of this process is a small sample of (at most) 10 credible galaxy candidates at z > 6.5 (from over 200 000 galaxies detected in the year-one UltraVISTA data) which we present in this paper. The first four of these appear to be robust galaxies at z > 6.5, and fitting to their stacked spectral energy distribution yields zphot = 6.98 ± 0.05 with a stellar mass M* ≃ 5 × 109 M⊙ and rest-frame ultraviolet (UV) spectral slope β ≃ −2.0 ± 0.2 (where fλ ∝ λβ). The next three are also good candidates for z > 6.5 galaxies, but the possibility that they are dwarf stars cannot be completely excluded. Our final subset of three additional candidates is afflicted not only by potential dwarf star contamination, but also contains objects likely to lie at redshifts just below z = 6.5. We show that the three even-brighter z ≳ 7 galaxy candidates reported in the COSMOS field by Capak et al. are in fact all lower redshift galaxies at z ≃ 1.5-3.5. Consequently the new z ≃ 7 galaxies reported here are the first credible z ≃ 7 Lyman-break galaxies discovered in the COSMOS field and, as the most UV luminous discovered to date at these redshifts, are prime targets for deep follow-up spectroscopy. We explore their physical properties, and briefly consider the implications of their inferred number density for the form of the galaxy luminosity function at z ≃ 7. [ABSTRACT FROM AUTHOR]

Context. The star-forming nature of long γ-ray burst (GRB) host galaxies provides invaluable constraints on the progenitors of GRBs and might open a short-cut to the characteristics of typical star-forming galaxies throughout the history of the Universe. Due to the absence of near-infrared (NIR) spectroscopy, however, detailed investigations, specifically a determination of the gas-phase metallicity of gamma-ray burst hosts, was largely limited to redshifts z 1 GRB host in unprecedented detail and investigate the relation between GRB hosts and field galaxies. Methods. We availed of VLT/X-shooter optical/NIR spectroscopy to measure the metallicity, electron density, star-formation rate (SFR), and reddening of the host of GRB 080605. Specifically, we used different strong-line diagnostics to robustly measure the gas-phase metallicity within the interstellar medium (ISM) for the first time based on [N ii] at this redshift. Results. The host of the energetic (Eγ,iso ~ 2 × 1053 erg) GRB 080605 at z ~ 1.64 is a morphologically complex, vigorously star-forming galaxy with an Hα-derived SFR of 31-6+12 M⊙ yr-1. Its ISM is significantly enriched with metals. Specifically, [N ii]/Hα = 0.14 ± 0.02, which yields an oxygen abundance 12 + log (O/H) between 8.3 and 8.6 depending on the adopted strong-line calibrator. This corresponds to values in the range of 0.4 − 0.8 Z⊙. For its measured stellar mass M* = 8.0-1.6+1.3 × 109 M⊙ and SFR, this value is consistent with the fundamental metallicity relation defined by star-forming field galaxies. The absence of strong Lyα emission constrains the escape fraction of resonantly-scattered Lyα photons to fesc ≲ 0.08. Conclusions. Our observations provide a detailed picture of the conditions in the ISM of a highly star-forming galaxy with irregular morphology at z ~ 1.6. They include the first robust metallicity measurement based on [N ii] for a GRB host at z > 1 and directly illustrate that GRB hosts are not necessarily metal-poor, both on absolute scales as well as relative to their stellar mass and SFR. GRB hosts could thus be fair tracers of the population of ordinary star-forming galaxies at high redshift. [ABSTRACT FROM AUTHOR]

We present the first search for galaxy counterparts of intervening high-z (2 < z < 3.6) sub-damped Lyα absorbers (sub-DLAs) and DLAs towards gamma-ray bursts (GRBs). Our final sample comprises five intervening sub-DLAs and DLAs in four GRB fields. To identify candidate galaxy counterparts of the absorbers we used deep optical- and near-infrared imaging, and low-, mid- and high-resolution spectroscopy acquired with 6-m to 10-m class telescopes, the Hubble and the Spitzer Space Telescopes. Furthermore, we used the spectroscopic information and spectral-energy-distribution fitting techniques to study them in detail. Our main result is the detection and spectroscopic confirmation of the galaxy counterpart of the intervening DLA at z = 3.096 in the field of GRB 070721B (zGRB = 3.6298) as proposed by other authors. We also identify good candidates for the galaxy counterparts of the two strong Mg ii absorbers at z = 0.6915 and 1.4288 towards GRB 050820A (zGRB = 2.615). The properties of the detected DLA galaxy are typical for Lyman-break galaxies (LBGs) at similar redshifts; a young, highly star-forming galaxy that shows evidence for a galactic outflow. This supports thehypothesis that a DLA can be the gaseous halo of an LBG. In addition, we report a redshift coincidence of different objects associated with metal lines in the same field, separated by 130–161 kpc. The high detection rate of three correlated structures on a length scale as short as ~150 kpc in two pairs of lines of sight is intriguing. The absorbers in each of these are most likely not part of the same gravitationally bound structure. They more likely represent groups of galaxies. [ABSTRACT FROM AUTHOR]

In this paper we describe the first data release of the UltraVISTA near-infrared imaging survey of the COSMOS field. We summarise the key goals and design of the survey and provide a detailed description of our data reduction techniques. We provide stacked, sky-subtracted images in YJHKs and narrow-band filters constructed from data collected during the first year of UltraVISTA observations. Our stacked images reach 5cr AB depths in an aperture of 2" diameter of ∼25 in Y and ∼24 in JHKs bands and all have subarcsecond seeing. To this 5σ limit, our Ks catalogue contains 216268 sources. We carry out a series of quality assessment tests on our images and catalogues, comparing our stacks with existing catalogues. The1σ astrometric rms in both directions for stars selected with 17.0 < Ks(AB) < 19.5 is∼0.08" in comparison to the publicly-available COSMOS ACS catalogues. Our images are resampled to the same pixel scale and tangent point as the publicly available COSMOS data and so may be easily used to generate multi-colour catalogues using this data. All images and catalogues presented in this paper are publicly available through ESO's "phase 3" archiving and distribution system and from the UltraVISTA web site. [ABSTRACT FROM AUTHOR]

We present new spectroscopic observations in a field containing the highest redshift cluster of the ESO Distant Cluster Survey (EDisCS). We measure galaxy redshifts and determine the velocity dispersions of the galaxy structures located in this field. Together with the main cluster Cl 1103.7-1245 (z = 0.9580; σclus = 522 ± 111 km s-1) we find a secondary structure at z = 0.9830, Cl 1103.7-1245c. We then characterize the galaxy properties in both systems, and find that they contain very different galaxy populations. The cluster Cl 1103.7-1245 hosts a mixture of passive elliptical galaxies and star-forming spirals and irregulars. In the secondary structure Cl 1103.7-1245c all galaxies are lower-mass star-forming irregulars and peculiars. In addition, we compare the galaxy populations in the Cl 1103.7-1245 z = 0.9580 cluster with those in lower redshift EDisCS clusters with similar velocity dispersions. We find that the properties of the galaxies in Cl 1103.7-1245 follow the evolutionary trends found at lower redshifts: the number of cluster members increases with time in line with the expected growth in cluster mass, and the fraction of passive early-type galaxies increases with time while star-forming late types become less dominant. Finally, we find that the mean stellar masses are similar in all clusters, suggesting that massive cluster galaxies were already present at z ∼ 1. [ABSTRACT FROM AUTHOR]

ABSTRACT Recently, the number of detected galaxy counterparts of z≳ 2 damped Lyman α absorbers in quasi-stellar object (QSO) spectra has increased substantially so we today have a sample of 10 detections. Møller et al. in the year 2004 made the prediction, based on a hint of a luminosity-metallicity relation for DLAs, that H i size should increase with increasing metallicity. In this Letter we investigate the distribution of impact parameter and metallicity that would result from the correlation between galaxy size and metallicity. We compare our observations with simulated data sets given the relation of size and metallicity. The observed sample presented here supports the metallicity-size prediction: the present sample of DLA galaxies is consistent with the model distribution. Our data also show a strong relation between impact parameter and column density of H i. We furthermore compare the observations with several numerical simulations and demonstrate that the observations support a scenario where the relation between size and metallicity is driven by feedback mechanisms controlling the star formation efficiency and outflow of enriched gas. [ABSTRACT FROM AUTHOR]