In order to understand the origin of the decreased star formation rate (SFR) efficiency of neutral atomic hydrogen gas measured in Damped Lyα Systems (DLAs) at z ~ 3, we measure the SFR efficiency of atomic gas at z ~ 1, z ~ 2, and z ~ 3 around star-forming galaxies. We create galaxy stacks in these three redshift bins, and measure the SFR efficiency by combining DLA absorber statistics with the observed rest-frame UV emission in the galaxies’ outskirts. We find that the SFR efficiency of Hi gas is ~ 3% of that predicted by the KS relation. We find no significant evolution in the SFR efficiency with redshift, although simulations and models predict a decreasing SFR efficiency with decreasing metallicity and thus with increasing redshift. We discuss possible explanations for this decreased efficiency without an evolution with redshift.

Gas and dust grains are fundamental components of the interstellar medium and significantly impact many of the physical processes driving galaxy evolution, such as star-formation, and the heating, cooling, and ionization of the interstellar material. Quasar absorption systems (QASs), which trace intervening galaxies along the sightlines to luminous quasars, provide a valuable tool to directly study the properties of the interstellar gas and dust in distant, normal galaxies. We have established the presence of silicate dust grains in at least some gas-rich QASs, and find that they exist at higher optical depths than expected for diffuse gas in the Milky Way. Differences in the absorption feature shapes additionally suggest variations in the silicate dust grain properties, such as in the level of grain crystallinity, from system-to-system. We present results from a study of the gas and dust properties of QASs with adequate archival IR data to probe the silicate dust grain properties. We discuss our measurements of the strengths of the 10 and 18 μm silicate dust absorption features in the QASs, and constraints on the grain properties (e.g., composition, shape, crystallinity) based on fitted silicate profile templates. We investigate correlations between silicate dust abundance, reddening, and gas metallicity, which will yield valuable insights into the history of star formation and chemical enrichment in galaxies.

The damped Lyman-α absorption-line systems (DLAs) that are observed in quasar spectra arise in neutral-gas-rich regions of intervening galaxies. With the highest neutral hydrogen column densities observed (N(HI) ⩾ 2 × 1020 atoms cm−2), they are known to trace the bulk of the neutral gas content of the Universe, and are thus powerful probes of galaxy formation and evolution. However, DLAs are extremely rare, and since the Lyman-α line falls in the UV for redshifts z < 1.65, not many are known at low redshift due to the limited availability of space data. Our HST surveys for DLAs in strong MgII absorbers have been successful at showing that MgII can be used as an unbiased tracer of DLAs. We present new results on their incidence, or redshift number density, dn/dz, and cosmological neutral gas mass density, ΩDLA, at redshifts 0.11 ⩽ z ⩽ 1.65, and incorporate results from higher and lower redshift studies in the literature to derive the evolution of neutral gas in the Universe.

We present two ongoing studies of gas phase abundances around high redshift quasars. First, we examine broad emission line (BEL) metallicities for 29 quasars with 2.3 < z < 4.6 and far-infrared (far-IR) luminosities (LFIR) from 1013.4 to ≤ 1012.2 L⊙, corresponding to star formation rates (SFRs) of 6740 to ≤ 1360 M⊙ yr−1. Quasar samples sorted by LFIR might represent an evolutionary sequence if SFRs in quasar hosts generally diminish across quasar lifetimes. We create three composite spectra from rest-frame ultra-violet Sloan Digital Sky Survey spectra with increasing far-IR luminosity. We measure the N V(λ1240)/C IV(λ1550) and Si IV(λ1397)+O IV](λ1402)/C IV(λ1550) emission line flux ratios for each composite and find uniformly high (~5-10 times solar) metallicities for the three composites, and no evidence for changes in metal enrichment with changes in ongoing SFR. Second, we present preliminary results from the largest ever survey of high resolution associated absorption line (AAL) region metallicities and physical properties in a sample of high redshift (z > 3) quasars. This includes five quasars with previously known AALs at z > 4 and two well measured z ~3 quasars with unusually rich absorption spectra. We determine well-constrained metallicities of about twice solar for five AAL systems. We find a range of lower limits for AAL metallicities in the z > 4 quasars from 1/100ths solar to 3 times solar. Overall, these results for typically super-solar gas-phase metallicities near quasars are consistent with evolutionary schemes where the major episodes of star formation in the host galaxies occur before the visibly luminous quasar phase. High SFRs (comparable to ULIRGs) in the host galaxies are not clearly linked to younger or chemically less mature quasar environments.

We present preliminary results from the largest-ever survey of high-resolution associated absorption line (AAL) region metallicities and physical properties in a sample of high redshift (z > 3) quasars.

Quasar feedback has been invoked as a major mechanism for influencing large-scale cosmological structure. To quantify to what extent they affect the real universe, one needs to measure the mechanical energy output of quasars and assess the ability of this energy to produce the feedback. We have developed an observational/modeling program that has yielded the first reliable kinetic luminosity determinations of quasar broad absorption line (BAL) outflows, and have demonstrated that energetically they are indeed a major contributor to AGN feedback.

Broad absorption lines (BALs), seen in a small fraction of both the radio-quiet and radio-loud quasar populations, are probably caused by the outflow of gas with high velocities and are part of the accretion process. The presence of BALs is due to a geometrical effect and/or it is connected with the quasar evolution. Using the final release of FIRST survey combined with a catalog of BAL QSOs from SDSS/DR3, we have constructed a new sample of compact radio-loud BAL QSOs, which constitutes the majority of radio-loud BAL QSOs. The main goal of this project is to study the origin of BALs by analysis of the BAL QSOs radio morphology, orientation, and jet evolution using the European VLBI Network (EVN) at 1.6 GHz and the Very Long Baseline Array (VLBA) at 5 and 8.4 GHz.

A complementary method to the emission selection of high-redshift galaxies consists in the observation of absorbers along the line of sight toward a background quasar. This selection technique has a constant sensitivity at all redshifts up to z = 6 (i.e. no redshift desert) and allow to select all types of galaxies regardless of their luminosity or star formation rate. The highest column density absorbers, the Damped Lyman-α (DLAs) systems, in particular, can be used to determine the cosmic evolution of HI gas in the Universe, ΩHI, and the global metallicity in the gas phase. Since stars are known to form from HI gas, ΩHI provides an indirect tracer of the history of star formation. Recent results from several parallel VLT programmes aiming at determining the cosmological evolution of the metallicity in the neutral gas phase are presented.