2014/02/21 by N. Gupta, Gupta, N., R. Srianand +8
Physics and Astronomy · #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.48550/arxiv.1402.5219
4 pages, 1 fugure; to appear in the proceedings of "The Metrewavelength Sky" conference held at NCRA, Pune, from December 9-13 2013
arxiv created 2014/02/21 · openalex publication_date 2014/02/21 · arxiv updated 2014/02/24 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We present recent results from our searches of 21-cm absorption using GBT, GMRT, VLBA and WSRT to trace the evolution of cold gas in galaxies. Using ~130 sight lines with 21-cm absorption measurements, we find that within the measurement uncertainty, the 21-cm detection rate in strong MgII systems is constant over 0.5<z<1.5. Since stellar feedback processes are expected to diminish the filling factor of CNM over 0.5<z<1, this lack of evolution in the 21-cm detection rate in MgII absorbers is intriguing. Further, we find that if the majority of 21-cm absorbers arise from DLAs then the cross-section of 21-cm absorbing gas i.e. cold neutral medium amongst DLAs has increased from z=3.5 to z=0.5. In a sample of 13 z>2 DLAs with both 21-cm and H2 (another tracer of cold gas) absorption measurements, we report two new H2 detections and find that in 8/13 cases neither 21-cm nor H2 is detected. This confirms that the HI gas in z>2 DLAs is predominantly warm. Interestingly, there are two cases where 21-cm absorption is not detected despite the presence of H2 with evidence for the presence of cold gas. This can be explained if H2 components seen in DLA are compact (<15 pc) and contain <10% of the total N(HI). We briefly discuss results from our ongoing survey to identify 21-cm absorbers at low-z to establish connection between 21-cm absorbers and galaxies, and constrain the extent of absorbing gas.