Séminaire/Seminar Galaxies |
| « On the evolution of Omega_HI over cosmological time scales » |
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Tayyaba Zafar |
| 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 Lya absorbers (DLAs) and sub-damped Lya 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, down to the sub-DLA limit is determined. The redshift evolution of column density distribution is also determined, indicating presence of more sub-DLAs at high redshift as compared to low redshift. The column density distribution function is further used to determine the HI gas mass density, at 1.5 < z < 5.0. The complete sample shows that sub-DLAs contribute 10-20% to the total gas mass density. In agreement with previous studies, no evolution of gas mass density 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. |
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jeudi 18 avril 2013 - 11:30 Salle 281 Institut d'Astrophysique de Paris |
| Page web du séminaire / Seminar's webpage |