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arXiv · 1402.5219

Galaxies in HI 21-cm absorption at z<3.5

N. Gupta·R. Srianand·P. Petitjean·P. Noterdaeme·E. Momjian
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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 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.

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N. Gupta, R. Srianand, P. Petitjean, P. Noterdaeme, E. Momjian. 2014-02-21. Galaxies in HI 21-cm absorption at z<3.5. https://arxiv.org/abs/1402.5219

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