The ESO UVES advanced data products quasar sample

Abstract

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.

The neutral hydrogen cosmological mass density atz= 5

“…This fraction is 15-30 per cent at z = 3, depending on the assumed N H I distribution (e.g. O'Meara et al 2007;Noterdaeme et al 2009;Prochaska, O'Meara & Worseck 2010;Zafar et al 2013). To parametrize this uncertainty, we introduce a correction factor δ H I ≡ H I / DLA H I to convert between DLA H I , which we measure, and H I .…”

The ESO UVES advanced data products quasar sample – III. Evidence of bimodality in the [N/α] distribution

“…The data were post-processed and analysed to look for the DLAs and sub-DLAs they contain. The search resulted in a sample of 197 DLAs and sub-DLAs, part of which was used to compute the statistical properties of quasar absorbers and the consequences on the cosmological evolution of neutral gas mass (Zafar et al 2013a). The wavelength coverage of the EUADP spectra is such that it allows for the detection of N i lines from 1.65 < z abs < 4.74.…”

The ESO UVES Advanced Data Products Quasar Sample – IV. On the deficiency of argon in DLA systems

“…Details on building and processing of the EUADP sample are presented in Zafar et al (2013b). This EUADP sample of 250 quasar spectra has been used to study DLAs/sub-DLAs (Zafar et al 2013a). Indeed, 197 DLAs and sub-DLAs have been reported in these quasar spectra, thus providing the ideal parent sample for the study of rare elements in quasar absorbers.…”