***********************************************************
OATS-UNI/TS SEMINAR
***********************************************************
Speaker: Tayyaba Zafar (Obs. de Marseille, France)

Title: No evolution of Omega_HI over cosmological scales
Date: Monday, October 29th, 2012
Time: 15:00
Venue: Villa Bazzoni
***********************************************************
Abstract: Damped absorbers seen in the spectra of background quasars are a unique probe to select HI rich galaxies. These galaxies allow to estimate neutral gas mass over cosmological scales, which is a possible indicator of gas consumption as star formation proceeds. The damped Lyα absorbers (DLAs) and sub-damped absorbers (sub-DLAs) are believed to contain a large fraction of neutral gas mass in the Universe. A search for DLAs and sub-DLAs is made in the reduced archival Ultraviolet Visual Echelle Spectrograph (UVES) dataset of 250 quasars. Because of a chosen redshift window a statistical analysis on 195 quasars is performed. For better statistics, the dataset of archival UVES quasars is analyzed in conjunction with other DLA and sub-DLA samples from the literature. Using the sample, redshift evolution of the number density and the line density are derived for DLAs and sub-DLAs and compared with the Lyman limit systems (LLSs) from the literature. Furthermore, the column density distribution, f_HI(N,z), down to the sub-DLA limit is determined. The redshift evolution of column density distribution is also determined, indicating the presence of more sub-DLAs at high redshift as compared to low redshift. f_HI(N,z) is further used to determine the HI gas mass density, Omega_HI, at 1.5 < z < 5.0. The complete sample shows that sub-DLAs contribute 10-20 % to the total Omega_HI. In agreement with previous studies, no evolution of Omega_HI is seen from low redshift to high redshift, suggesting that star formation solely cannot explain this non-evolution and replenishment of gas, and/or recombination of ionized gas is needed.
************************************************************
Contact: Valentina D'Odorico (OATS)