{
  "id": "1402.5219",
  "version": "v1",
  "published": "2014-02-21T07:07:17.000Z",
  "updated": "2014-02-21T07:07:17.000Z",
  "title": "Galaxies in HI 21-cm absorption at z<3.5",
  "authors": [
    "N. Gupta",
    "R. Srianand",
    "P. Petitjean",
    "P. Noterdaeme",
    "E. Momjian"
  ],
  "comment": "4 pages, 1 fugure; to appear in the proceedings of \"The Metrewavelength Sky\" conference held at NCRA, Pune, from December 9-13 2013",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "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 H$_2$ (another tracer of cold gas) absorption measurements, we report two new H$_2$ detections and find that in 8/13 cases neither 21-cm nor H$_2$ 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 H$_2$ with evidence for the presence of cold gas. This can be explained if H$_2$ 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.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-02-21T07:07:17.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "cold gas",
      "absorption measurements",
      "strong mgii systems",
      "hi gas",
      "sight lines"
    ],
    "tags": [
      "conference paper"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 4,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1282125,
      "adsabs": "2014arXiv1402.5219G"
    }
  }
}