Damped Lyman-alpha Absorption Research Articles

The alpha -element enrichment of gas in distant galaxies

The chemical evolution of distant galaxies cannot be assessed from observations of individual stars, in contrast to the case of nearby galaxies. On the other hand, the study of the interstellar medium (ISM) offers an alternative way to reveal important properties of the chemical evolution of distant galaxies. The chemical enrichment of the ISM is produced by all the previous generations of stars and it is possible to precisely determine the metal abundances in the neutral ISM in galaxies. The chemical abundance patterns in the neutral ISM are determined by the gas metallicity, presence of dust (the depletion of metals into dust grains), and possible deviations due to specific nucleosynthesis, for example, alpha -element enhancements. We aim to derive the metallicities, dust depletion, and alpha -element enhancements in the neutral ISM of gas-rich mostly-metal-poor distant galaxies (Damped Lyman-alpha absorbers, DLAs). Furthermore, we aim to constrain the distribution of alpha -element enhancements with metallicity in these galaxies. We collected a literature sample of column density measurements of O, Mg, Si, S, Ti, Cr, Fe, Ni, Zn, P, and Mn in the neutral ISM of DLAs at redshifts of $0.60 < z < 3.40$. We used this sample to define a golden sample of DLAs with constrained observations of Ti and at least one other alpha -element. By studying the abundance patterns, we determined the amount of dust depletion, solely based on the observed relative abundances of the alpha -elements. We then used the abundances of Fe-peak elements to determine the overall metallicity of each system, after correcting for dust depletion. In addition, we studied the deviations from the basic (linear) abundance patterns. We divided our sample into two groups of galaxies based on the widths of their absorption lines ($ $ above or below 100 which may be considered as a proxy for their dynamical mass. We characterised the distribution of the alpha -element enhancements as a function of metallicity for the galaxy population as a whole, by fitting a piecewise function (plateau, decline, plateau) to the data. We observed systematic deviations from the basic abundance patterns for O, Mg, Si, S, Ti, and Mn, which we interpreted as alpha -element enhancements and a Mn underabundance. The distribution of the alpha -element enhancements with metallicity is different in the high-$ $ and low-$ $ groups of galaxies. We constrained the metallicity of the alpha -element knee for the high-$ $ and low-$ $ groups of galaxies to be $-$1.02pm 0.15 dex and $-$1.84pm 0.11 dex, respectively. The average alpha -element enhancement at the high-plateau is alpha /Fe =0.38pm 0.07 dex. On the other hand, Mn shows an underabundance in all DLAs in the golden sample of $-$0.36pm 0.07 dex, on average. We have constrained, for the first time, the distribution of the alpha -element enhancement with metallicity in the neutral ISM in distant galaxies. Less massive galaxies show an alpha -element knee at lower metallicities than more massive galaxies. This can be explained by a lower star formation rate in less massive galaxies. If this collective behaviour can be interpreted in the same way as it is for individual systems, this would suggest that more massive and metal-rich systems evolve to higher metallicities before the contribution of SN-Ia to alpha /Fe levels out that of core-collapse SNe. This finding may plausibly be supported by different SFRs in galaxies of different masses. Overall, our results offer important clues to the study of chemical evolution in distant galaxies.

A successful search for intervening 21 cm H i absorption in galaxies at 0.4 < z <1.0 with the Australian square kilometre array pathfinder (ASKAP)

ABSTRACT We have used the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope to search for intervening 21 cm neutral hydrogen (H i) absorption along the line of sight to 53 bright radio continuum sources. Our observations are sensitive to H i column densities typical of Damped Lyman Alpha absorbers (DLAs) in cool gas with an H i spin temperature below about 300–500 K. The six-dish Boolardy Engineering Test Array (BETA) and twelve-antenna Early Science array (ASKAP-12) covered a frequency range corresponding to redshift 0.4 < z < 1.0 and 0.37 < z < 0.77, respectively, for the H i line. Fifty of the 53 radio sources observed have reliable optical redshifts, giving a total redshift path Δz = 21.37. This was a spectroscopically untargeted survey, with no prior assumptions about the location of the lines in redshift space. Four intervening H i lines were detected, two of them new. In each case, the estimated H i column density lies above the DLA limit for H i spin temperatures above 50–80 K, and we estimate a DLA number density at redshift z ∼ 0.6 of $n(z)=0.19^{+0.15 }_{ -0.09}$. This value lies somewhat above the general trend of n(z) with redshift seen in optical DLA studies. Although the current sample is small, it represents an important proof of concept for the much larger 21 cm First Large Absorption Survey in H i (FLASH) project to be carried out with the full 36-antenna ASKAP telescope, probing a total redshift path $\Delta z\sim \, 50,000$.

Multicomponent H2 in DLA at zabs = 2.05: physical conditions through observations and numerical models★

We perform detailed spectroscopic analysis and numerical modelling of an H2-bearing damped Lyman-alpha absorber (DLA) at zabs = 2.05 towards the quasar FBQS J2340-0053. Metal absorption features arise from fourteen components spread over $\Delta v_{90}$ = 114 km s$^{-1}$, seven of which harbour H2. Column densities of atomic and molecular species are derived through Voigt profile analysis of their absorption lines. We measure total N(H I), N(H2) and N(HD) to be 20.35+/-0.05, 17.99+/-0.05 and 14.28+/-0.08 (log cm$^{-2}$) respectively. H2 is detected in the lowest six rotational levels of the ground vibrational state. The DLA has metallicity, Z = 0.3 Z$_\sun$ ([S/H] = -0.52+/-0.06) and dust-to-gas ratio, $\kappa$ = 0.34+/-0.07. Numerical models of the H2 components are constrained individually to understand the physical structure of the DLA. We conclude that the DLA is subjected to the metagalactic background radiation and cosmic ray ionization rate of $\sim$ 10$^{-15.37}$ s$^{-1}$. Dust grains in this DLA are smaller than grains in the Galactic interstellar medium. The inner molecular regions of the H2 components have density, temperature and gas pressure in the range 30-120 cm$^{-3}$, 140-360 K and 7,000-23,000 cm$^{-3}$ K respectively. Micro-turbulent pressure is a significant constituent of the total pressure, and can play an important role in these innermost regions. Our H2 component models enable us to constrain component-wise N(H I), and elemental abundances of sulphur, silicon, iron and carbon. We deduce the line-of-sight thickness of the H2-bearing parts of the DLA to be 7.2 pc.

Multiple Absorption Systems in the Lines of Sight to Quadruply Lensed Quasar H1413+1143 As a Probe of the Circumgalactic medium around Dwarf Galaxy

AbstractWe present the first measurement of differences in MgII absorption strength in multiple intervening absorbers, which are also identified as (sub-)Damped Lyman alpha absorption systems, in the four spectra of the quadruply lensed quasar H1413+1143, often referred to the “Cloverleaf”, from highly spatial resolution and high signal-to-noise spectroscopy with an optical multi-mode spectrograph, the Kyoto tridimentional spectrograph II on board the Subaru telescope. The detection of significant MgII absorptions in multiple components in the spatially-resolved spectra suggests that chemical enrichment differs at least on scale of about 10 kpc within the separation of sightlines. For, a DLA system at redshift zabs = 1.66, the rest equivalent widths of MgII absorption lines change by factors up to 6, which is similar to those of HI absorption lines. This suggests that (inhomogeneous) cold absorbers which give rise to strong HI/MgII absorptions dwell on a scale within 10 kpc in the circumgalactic medium (CGM).

Far-UV HST  Spectroscopy of an Unusual Hydrogen-poor Superluminous Supernova: SN2017egm

Abstract SN2017egm is the closest (z = 0.03) H-poor superluminous supernova (SLSN-I) detected to date, and a rare example of an SLSN-I in a massive, metal-rich galaxy. We present the HST UV and optical spectra covering 1000–5500 Å, taken at +3 day relative to the peak. Our data reveal two absorption systems at redshifts matching the host galaxy NGC 3191 (z = 0.0307) and its companion galaxy (z = 0.0299) 73″ apart. Weakly damped Lyα absorption lines are detected at these two redshifts, with H i column densities of (3.0 ± 0.8) × 1019 and (3.7 ± 0.9) × 1019 cm−2, respectively. This is an order of magnitude smaller than the H i column densities in the disks of nearby galaxies (>1010 M ⊙) and suggests that SN2017egm is on the near side of NGC 3191 and has a low host extinction (E(B − V) ∼ 0.007). Using unsaturated metal absorption lines, we find that the host of SN2017egm probably has a solar or higher metallicity and is unlikely to be a dwarf companion to NGC 3191. Comparison of early-time UV spectra of SN2017egm, Gaia16apd, iPTF13ajg, and PTF12dam finds that the continuum at λ > 2800 Å is well fit by a blackbody, whereas the continuum at λ < 2800 Å is considerably below the model. The degree of UV suppression varies from source to source, with the 1400–2800 Å continuum flux ratio of 1.5 for Gaia16apd and 0.4 for iPTF13ajg. This cannot be explained by the differences in magnetar power or blackbody temperature. Finally, the UV spectra reveal a common set of seven broad absorption features and their equivalent widths are similar (within a factor of 2) among the four events.

The metallicity distribution of H i systems in the EAGLE cosmological simulations

The metallicity of strong HI systems, spanning from damped Lyman-alpha absorbers (DLAs) to Lyman-limit systems (LLSs) is explored between z = 5->0 using the EAGLE high-resolution cosmological hydrodynamic simulation of galaxy formation. The metallicities of LLSs and DLAs steadily increase with time in agreement with observations. DLAs are more metal rich than LLSs, although the metallicities in the LLS column density range (NHI = 10^17 -10^20 cm^-2) are relatively flat, evolving from a median HI-weighted metallicity of Z<10^-2 Zsol at z = 3 to ~10^-0.5 Zsol by z = 0. The metal content of HI systems tracks the increasing stellar content of the Universe, holding ~5% of the integrated total metals released from stars at z = 0. We also consider partial LLS (pLLS, NHI = 10^16-10^17 cm^-2) metallicities, and find good agreement with Wotta et al. (2016) for the fraction of systems above (37%) and below (63%) 0.1 Zsol. We also find a large dispersion of pLLS metallicities, although we do not reproduce the observed metallicity bimodality and instead we make the prediction that a larger sample will yield more pLLSs around 0.1 Zsol. We under-predict the median metallicity of strong LLSs, and predict a population of Z < 10^-3 Zsol DLAs at z > 3 that are not observed, which may indicate more widespread early enrichment in the real Universe compared to EAGLE.

Correlations in the three-dimensional Lyman-alpha forest contaminated by high column density absorbers

Correlations measured in three dimensions in the Lyman-alpha forest are contaminated by the presence of the damping wings of high column density (HCD) absorbing systems of neutral hydrogen (HI; having column densities $N(\mathrm{HI}) > 1.6\times10^{17}\,\mathrm{atoms}\,\mathrm{cm}^{-2}$), which extend significantly beyond the redshift-space location of the absorber. We measure this effect as a function of the column density of the HCD absorbers and redshift by measuring 3D flux power spectra in cosmological hydrodynamical simulations from the Illustris project. Survey pipelines exclude regions containing the largest damping wings. We find that, even after this procedure, there is a scale-dependent correction to the 3D Lyman-alpha forest flux power spectrum from residual contamination. We model this residual using a simple physical model of the HCD absorbers as linearly biased tracers of the matter density distribution, convolved with their Voigt profiles and integrated over the column density distribution function. We recommend the use of this model over existing models used in data analysis, which approximate the damping wings as top-hats and so miss shape information in the extended wings. The simple 'linear Voigt model' is statistically consistent with our simulation results for a mock residual contamination up to small scales ($|k| < 1\,h\,\mathrm{Mpc}^{-1}$). It does not account for the effect of the highest column density absorbers on the smallest scales (e.g., $|k| > 0.4\,h\,\mathrm{Mpc}^{-1}$ for small damped Lyman-alpha absorbers; HCD absorbers with $N(\mathrm{HI}) \sim 10^{21}\,\mathrm{atoms}\,\mathrm{cm}^{-2}$). However, these systems are in any case preferentially removed from survey data. Our model is appropriate for an accurate analysis of the baryon acoustic oscillations feature. It is additionally essential for reconstructing the full shape of the 3D flux power spectrum.

An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way’s circumgalactic medium and the Local Group

To characterize the absorption properties of this circumgalactic medium (CGM) and its relation to the LG we present the so-far largest survey of metal absorption in Galactic high-velocity clouds (HVCs) using archival ultraviolet (UV) spectra of extragalactic background sources. The UV data are obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST) and are supplemented by 21 cm radio observations of neutral hydrogen. Along 270 sightlines we measure metal absorption in the lines of SiII, SiIII, CII, and CIV and associated HI 21 cm emission in HVCs in the velocity range |v_LSR|=100-500 km s^-1. With this unprecedented large HVC sample we were able to improve the statistics on HVC covering fractions, ionization conditions, small-scale structure, CGM mass, and inflow rate. For the first time, we determine robustly the angular two point correlation function of the high-velocity absorbers, systematically analyze antipodal sightlines on the celestial sphere, and compare the absorption characteristics with that of Damped Lyman alpha absorbers (DLAs) and constrained cosmological simulations of the LG. Our study demonstrates that the Milky Way CGM contains sufficient gaseous material to maintain the Galactic star-formation rate at its current level. We show that the CGM is composed of discrete gaseous structures that exhibit a large-scale kinematics together with small-scale variations in physical conditions. The Magellanic Stream clearly dominates both the cross section and mass flow of high-velocity gas in the Milky Way's CGM. The possible presence of high-velocity LG gas underlines the important role of the local cosmological environment in the large-scale gas-circulation processes in and around the Milky Way (abridged).

The HighAVQuasar Survey: Az = 2.027 metal-rich damped Lyman-αabsorber towards a red quasar atz = 3.21

To fully exploit the potential of quasars as probes of cosmic chemical evolution and the internal gas dynamics of galaxies it is important to understand the selection effects behind the quasar samples and in particular if the selection criteria exclude foreground galaxies with certain properties (most importantly a high dust content). Here we present spectroscopic follow-up from the 10.4-m GTC telescope of a dust-reddened quasar, eHAQ0111+0641, from the extended High A_V Quasar (HAQ) survey. We find that the z=3.21 quasar has a foreground Damped Lyman-alpha Absorber (DLA) at z=2.027 along the line of sight. The DLA has very strong metal lines due to a moderately high metallicity (with an inferred lower limit of 25% of the solar metallicity), but a very large gas column density along the line-of-sight in its host galaxy. This discovery is further evidence that there is a dust bias affecting the census of metals, caused by the combined effect of dust obscuration and reddening, in existing samples of z>2 DLAs. The case of eHAQ0111+0641 illustrates that dust bias is not only caused by dust obscuration, but also dust reddening.

Observed Faraday Effects in Damped Lyα Absorbers and Lyman Limit Systems: The Magnetized Environment of Galactic Building Blocks at Redshift = 2

Abstract Protogalactic environments are typically identified using quasar absorption lines and can manifest as Damped Lyman-alpha Absorbers (DLAs) and Lyman Limit Systems (LLSs). We use radio observations of Faraday effects to test whether these galactic building blocks host a magnetized medium, by combining DLA and LLS detections with 1.4 GHz polarization data from the NRAO VLA Sky Survey (NVSS). We obtain a control, a DLA, and an LLS sample consisting of 114, 19, and 27 lines of sight, respectively. Using a Bayesian framework and weakly informative priors, we are unable to detect either coherent or random magnetic fields in DLAs: the regular coherent fields must be μG, and the lack of depolarization suggests the weakly magnetized gas in DLAs is non-turbulent and quiescent. However, we find a mild suggestive indication that LLSs have coherent magnetic fields, with a 71.5% probability that LLSs have higher than a control, although this is sensitive to the redshift distribution. We also find a strong indication that LLSs host random magnetic fields, with a 95.5% probability that LLS lines of sight have lower polarized fractions than a control. The regular coherent fields within the LLSs must be μG, and the magnetized gas must be highly turbulent with a typical turbulent length scale on the order of ≈5–20 pc. Our results are consistent with the standard dynamo paradigm, whereby magnetism in protogalaxies increases in coherence over cosmic time, and with a hierarchical galaxy formation scenario, with the DLAs and LLSs exploring different stages of magnetic field evolution in galaxies.

Evolution of the dust-to-metals ratio in high-redshift galaxies probed by GRB-DLAs

Context. Several issues regarding the nature of dust at high redshift remain unresolved: its composition, its production and growth mechanisms, and its effect on background sources. Aims. We provide a more accurate relation between dust depletion levels and dust-to-metals ratio (DTM), and to use the DTM to investigate the origin and evolution of dust in the high-redshift Universe via Gamma-ray burst damped Lyman-alpha absorbers (GRB-DLAs). Methods. We use absorption-line measured metal column densities for a total of 19 GRB-DLAs, including five new GRB afterglow spectra from VLT/X-shooter. We use the latest linear models to calculate the dust depletion strength factor in each DLA. Using these values we calculate total dust and metal column densities to determine a DTM. We explore the evolution of DTM with metallicity, and compare it to previous trends in DTM measured with different methods. Results. We find significant dust depletion in 16 of our 19 GRB-DLAs, yet 18 of the 19 have a DTM significantly lower than the Milky Way. We find that DTM is positively correlated with metallicity, which supports a dominant ISM grain-growth mode of dust formation. We find a substantial discrepancy between the dust content measured from depletion and that derived from the total V-band extinction, $A_V$ , measured by fitting the afterglow SED. We advise against using a measurement from one method to estimate that from the other until the discrepancy can be resolved.

The galaxy counterpart of the high-metallicity and 16 kpc impact parameter DLA towards Q 0918+1636 – a challenge to galaxy formation models?

The quasar Q0918+1636 (z=3.07) has an intervening high-metallicity Damped Lyman-alpha 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 has an almost solar metallicity. It is shown, that a novel type of cosmological galaxy formation models, invoking a new SNII feedback prescription, the Haardt & Madau (2012) UVB field and explicit treatment of UVB self-shielding, can reproduce the observed characteristics of the DLA. UV radiation from young stellar populations in the galaxy, in particular in the photon energy range 10.36-13.61 eV (relating to Sulfur II abundance), are also considered in the analysis. It is found that a) for L~L* galaxies (at z=2.58), about 10% of the sight-lines through the galaxies at impact parameter 16.2 kpc will display a Sulfur II column density N(SII)$>$ 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 probability distribution of galaxy SFR peaks near the value observed for the DLA galaxy counterpart of ~27 Msun/yr. It is argued, that the bulk of the alpha-elements, like Sulfur, traced by the high metal column density, b=16.2 kpc absorption lines, were produced by evolving young stars in the inner galaxy, and later transported outward by galactic winds.

Physical conditions in three high-zH2-bearing DLAs: implications for grain size

We present results of our numerical simulation of three H2-bearing damped Lyman alpha absorbers (DLAs) in the redshift interval ~ 2-3. The systems we have modelled are the DLAs at zabs = 2.3377 towards the quasar LBQS 1232+0815, at zabs = 2.41837 towards SDSS J143912.04+111740.5 and at zabs = 2.6265 towards FBQS J081240.6+320808. We have used the spectral synthesis code CLOUDY to simulate the physical environment of these DLAs, and constrain the density, radiation field, geometry and dust-grain properties of the DLAs self-consistently based on the observed column densities of various atomic and molecular species such as H I, fine structure lines of C I and the rotational level population of H2. In our models, we explore the effect of grain size distribution on the predicted column densities of different species. Within the allowed uncertainties in the inferred dust-to-gas ratio, both models with standard ISM grains and smaller-sized grains reproduce the observations equally well. Improved constraints on dust-to-gas ratio and line-of-sight extinction are important for probing the grain size distribution in high-z DLAs. We find the H2-bearing clouds to have line-of-sight thickness in the range 1-6 pc, consistent with what has been found using partial coverage or 21-cm observations in some high-z DLAs.

Dispersion in DLA metallicities and deuterium abundances

AbstractRecent chemical abundance measurements of damped Lyman-alpha absorbers (DLAs) revealed a large intrinsic scatter in their metallicities. We discuss a semi-analytic model that was specifically designed to study this scatter by tracing the chemical evolution of the interstellar matter in small regions of the Universe with different mean density, from over- to underdense regions. It is shown that different histories of structure formation in these regions are reflected in the chemical properties of the proto-galaxies. We also address deuterium abundance measurements, which constitute a complementary probe of the star formation and infall histories.

A quasar reddened by a sub-parsec-sized, metal-rich and dusty cloud in a damped Lyman α absorber atz= 2.13

We present a detailed analysis of a red quasar at z=2.32 with an intervening damped Lyman-alpha 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 $27 \pm 6$ % 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 $A(V)_{\rm DLA}=0.28 \pm 0.01|_{\rm stat} \pm 0.07|_{\rm sys}$. 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 underrepresented in current samples of DLAs.

Damped Lyman α absorbers as a probe of stellar feedback

We examine the abundance, clustering and metallicity of Damped Lyman-alpha Absorbers (DLAs) in a suite of hydrodynamic cosmological simulations using the moving mesh code AREPO. We incorporate models of supernova and AGN feedback, as well as molecular hydrogen formation. We compare our simulations to the column density distribution function at $z=3$, the total DLA abundance at $z=2-4$, the measured DLA bias at $z=2.3$ and the DLA metallicity distribution at $z=2-4$. Our preferred models produce populations of DLAs in good agreement with most of these observations. The exception is the DLA abundance at $z < 3$, which we show requires stronger feedback in $10^{11-12} \, h^{-1} M_\odot$ mass halos. While the DLA population probes a wide range of halo masses, we find the cross-section is dominated by halos of mass $10^{10} - 10^{11} \, h^{-1} M_\odot$ and virial velocities $50 - 100 \;\mathrm{km/s}$. The simulated DLA population has a linear theory bias of $1.7$, whereas the observations require $2.17 \pm 0.2$. We show that non-linear growth increases the bias in our simulations to $2.3$ at $k=1\; \mathrm{Mpc/}h$, the smallest scale observed. The scale-dependence of the bias is, however, very different in the simulations compared against the observations. We show that, of the observations we consider, the DLA abundance and column density function provide the strongest constraints on the feedback model.

The bias of DLAs at z∼2.3: evidence for very strong stellar feedback in shallow potential wells

We discuss the recent Baryon Oscillation Spectroscopic Survey measurement of a rather high bias factor for the host galaxies/haloes of Damped Lyman-alpha Absorbers (DLAs), in the context of our previous modelling of the physical properties of DLAs within the $\Lambda$ cold dark matter paradigm. Joint modelling of the column density distribution, the velocity width distribution of associated low ionization metal absorption, and the bias parameter suggests that DLAs are hosted by galaxies with dark matter halo masses in the range $10 < \log M_v < 12$, with a rather sharp cutoff at the lower mass end, corresponding to virial velocities of 35 km/sec. The observed properties of DLAs appear to suggest efficient (stellar) feedback in haloes with masses/virial velocities below the cutoff and a large retained baryon fraction (> 35 %) in haloes above the cutoff.

THE METALLICITY AND DUST CONTENT OF A REDSHIFT 5 GAMMA-RAY BURST HOST GALAXY

Observations of the afterglows of long gamma-ray bursts (GRBs) allow the study of star-forming galaxies across most of cosmic history. Here we present observations of GRB 111008A from which we can measure metallicity, chemical abundance patterns, dust-to-metals ratio and extinction of the GRB host galaxy at z=5.0. The host absorption system is a damped Lyman-alpha absorber (DLA) with a very large neutral hydrogen column density of log N(HI)/cm^(-2) = 22.30 +/- 0.06, and a metallicity of [S/H]= -1.70 +/- 0.10. It is the highest redshift GRB with such a precise metallicity measurement. The presence of fine-structure lines confirms the z=5.0 system as the GRB host galaxy, and makes this the highest redshift where Fe II fine-structure lines have been detected. The afterglow is mildly reddened with A_V = 0.11 +/- 0.04 mag, and the host galaxy has a dust-to-metals ratio which is consistent with being equal to or lower than typical values in the Local Group.

PRECIOUS METALS IN SDSS QUASAR SPECTRA. II. TRACKING THE EVOLUTION OF STRONG, 0.4 &lt;z&lt; 2.3 Mg II ABSORBERS WITH THOUSANDS OF SYSTEMS

We have performed an analysis of over 34,000 MgII doublets at 0.36 < z < 2.29 in Sloan Digital Sky Survey (SDSS) Data-Release 7 quasar spectra; the catalog, advanced data products, and tools for analysis are publicly available. The catalog was divided into 14 small redshift bins with roughly 2500 doublets in each, and from Monte-Carlo simulations, we estimate 50% completeness at rest equivalent width W_r ~ 0.8 Angstrom. The equivalent-width frequency distribution is described well by an exponential model at all redshifts, and the distribution becomes flatter with increasing redshift, i.e., there are more strong systems relative to weak ones. Direct comparison with previous SDSS MgII surveys reveal that we recover at least 70% of the doublets in these other catalogs, in addition to detecting thousands of new systems. We discuss how these surveys come by their different results, which qualitatively agree but, due to the very small uncertainties, differ by a statistically significant amount. The estimated physical cross-section of MgII-absorbing galaxy halos increased three-fold, approximately, from z = 0.4 --> 2.3, while the W_r >= 1 Angstrom absorber line density grew, dN_MgII/dX, by roughly 45%. Finally, we explore the different evolution of various absorber populations - damped Lyman-alpha absorbers, Lyman-limit systems, strong CIV absorbers, and strong and weaker MgII systems - across cosmic time (0 < z < 6).

The impact of different physical processes on the statistics of Lyman-limit and damped Lyman α absorbers

We compute the z = 3 neutral hydrogen column density distribution function f(NHI) for 19 simulations drawn from the OWLS project using a post-processing correction for self-shielding calculated with full radiative transfer of the ionising background radiation. We investigate how different physical processes and parameters affect the abundance of Lyman-limit systems (LLSs) and damped Lyman-alpha absorbers (DLAs) including: i) metal-line cooling; ii) the efficiency of feedback from SNe and AGN; iii) the effective equation of state for the ISM; iv) cosmological parameters; v) the assumed star formation law and; vi) the timing of hydrogen reionization . We find that the normalisation and slope, D = d log10 f /d log10 NHI, of f(NHI) in the LLS regime are robust to changes in these physical processes. Among physically plausible models, f(NHI) varies by less than 0.2 dex and D varies by less than 0.18 for LLSs. This is primarily due to the fact that these uncertain physical processes mostly affect star-forming gas which contributes less than 10% to f(NHI) in the the LLS column density range. At higher column densities, variations in f(NHI) become larger (approximately 0.5 dex at NHI = 10^22 cm^-2 and 1.0 dex at NHI = 10^23 cm^-2) and molecular hydrogen formation also becomes important. Many of these changes can be explained in the context of self-regulated star formation in which the amount of star forming gas in a galaxy will adjust such that outflows driven by feedback balance inflows due to accretion. Data and code to reproduce all figures can be found at the following url: https://bitbucket.org/galtay/hi-cddf-owls-1