Damped absorbers, seen in the spectra of background quasars, are unique probes to select H i-rich galaxies. These galaxies allow one to estimate the neutral gas mass over cosmological scales. The neutral gas mass is a possible indicator of gas consumption as star formation proceeds. The damped Lyα absorbers (DLAs; N H I ≥ 2 × 10 20 cm −2 ) and sub-DLAs (10 19 ≤ N H I ≤ 2 × 10 20 cm −2 ) are believed to contain a large fraction of neutral gas mass in the Universe. In Paper I of the series, we presented the results of a search for DLAs and sub-DLAs in the European Southern Observatory (ESO) Ultraviolet Visual Echelle Spectrograph (UVES) advanced data products dataset of 250 quasars. Here we use an unbiased subsample of sub-DLAs from this dataset to derive their statistical properties. We built a subset of 122 quasars ranging from 1.5 < z em < 5.0, suitable for statistical analysis. The statistical sample was analyzed in conjunction with other sub-DLA samples from the literature. This resulted in a combined sample of 89 sub-DLAs over a redshift path of Δz = 193. We derived the redshift evolution of the number density and the line density for sub-DLAs and compared them with the Lyman-limit systems (LLSs) and DLA measurements from the literature. The results indicate that these three classes of absorbers are evolving in the redshift interval 1.0 < z < 5.0. Thanks to the ESO UVES advanced data products data, we were able to determine the column density distribution, f H I (N, z), down to the sub-DLA limit. The flattening of f H I (N, z) in the sub-DLA regime is present in the observations. The redshift evolution of f H I (N, z) down to log N H I = 19.0 cm −2 is also presented, indicating that there are more sub-DLAs at high redshift than at low redshift. f H I (N, z) was also used to determine the neutral gas mass density, Ω g , at 1.5 < z < 5.0. The complete sample shows that sub-DLAs contribute 8-20% to the total Ω g from 1.5 < z < 5.0. In agreement with previous studies, no evolution of Ω g was observed from low to high redshift (i.e., 1.5 < z < 5.0), suggesting that star formation alone cannot explain this non-evolution and replenishment of gas and that recombination of ionized gas is needed.

Studies of extinction curves provide insights into the properties of interstellar dust. Until recently, however, very few extinction curves existed outside the local group. GRB afterglows are well suited to extinction studies due to their brightness, simple power-law spectra and their occurrence in distant star forming galaxies. In this paper we present results from the SED analysis of a sample of 41 GRB afterglows, from X-ray to NIR wavelengths. The sample is based on spectra from VLT-FORS, with additional data primarily from Swift. This is the largest sample of extinction curves outside the Local Group and, to date, the only extragalactic sample of absolute extinction curves based on spectroscopy. Estimates of the distribution of restframe visual extinctions, the extinction curves, and the intrinsic spectral shapes of GRB afterglows are obtained. Their correlation with H i column density as well as total and gas-phase metal column density are examined. The line-of-sight gas-to-dust and metals-to-dust ratios are determined and examined as a function of total column density, ISM metallicity and redshift. The intrinsic SEDs of the afterglows show that approximately half the sample require a cooling break between the optical and X-ray ranges. The broken power-law SEDs show an average change in the spectral index of Δβ = 0.51 with a very small standard deviation of 0.02 (excluding the outlier GRB 080210). This is consistent with the expectations from a simple synchrotron model. Such a close convergence of values suggests that the X-ray afterglows of GRBs may be used with considerably more confidence to set the absolute flux level and intrinsic spectral indices in the optical and UV. Of the sample, 63% are well described by a featureless (SMC-type) extinction curve. Almost a quarter of our sample is consistent with no significant extinction (typically A V 0.1). The 2175 Å extinction bump is detected unequivocally in 7% of our sample (3 GRBs), which all have A V > 1.0, while one afterglow has a very unusual extinction curve with a sharp UV rise. However, we can only say that the bump is not present in about a quarter of our sample because of low extinction or lack of coverage of the 2200 Å region. All the afterglows well fit with SMC type curves have moderate or low extinction, with A V < 0.65. This suggests that the SMC extinction curve is not as nearly-universal as previously believed and that extinction curves more similar to those found in the Galaxy and the LMC may be quite prevalent. We find an anti-correlation between gas-to-dust ratio and metallicity consistent with the Local Group relation; we find, however, no correlation between the metals-to-dust ratios and the metallicities, redshift and visual extinction; we find no strong correlation of the extinction column with metallicity either. Our metals-to-dust ratios derived from the soft X-ray absorption are always larger (3-30 times) than the Local Group value, which may mean that GRB hosts may be less efficient at turning their metals into dust. Howe...

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