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H I 21-cm absorption survey of quasar-galaxy pairs: distribution of cold gas around z < 0.4 galaxies

Abstract : We present the results from our survey of H I 21-cm absorption, using Giant Metrewave Radio Telescope, Very Large Array and Westerbork Radio Synthesis Telescope, in a sample of 55 z < 0.4 galaxies towards radio sources with impact parameters (b) in the range ∼0-35 kpc. In our primary sample (defined for statistical analyses) of 40 quasar-galaxy pairs, probed by 45 sightlines, we have found seven H I 21-cm absorption detections, two of which are reported here for the first time. Combining our primary sample with measurements having similar optical depth sensitivity (∫τdv ≤ 0.3 km s-1) from the literature, we find a weak anti-correlation (rank correlation coefficient = -0.20 at 2.42σ level) between ∫τdv and b, consistent with previous literature results. The covering factor of H I 21-cm absorbers (C21) is estimated to be 0.24^{+0.12}_{-0.08} at b ≤ 15 kpc and 0.06^{+0.09}_{-0.04} at b = 15-35 kpc. ∫τdv and C21 show similar declining trend with radial distance along the galaxy's major axis and distances scaled with the effective H I radius. There is also tentative indication that most of the H I 21-cm absorbers could be co-planar with the extended H I discs. No significant dependence of ∫τdv and C21 on galaxy luminosity, stellar mass, colour and star formation rate is found, though the H I 21-cm absorbing gas cross-section may be larger for the luminous galaxies. The higher detection rate (by a factor of ∼4) of H I 21-cm absorption in z < 1 damped Lyman-α systems compared to the quasar-galaxy pairs indicates towards small covering factor and patchy distribution of cold gas clouds around low-z galaxies.
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https://hal-insu.archives-ouvertes.fr/insu-03666210
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Submitted on : Thursday, May 12, 2022 - 4:31:54 PM
Last modification on : Saturday, May 14, 2022 - 3:03:49 AM

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R. Dutta, R. Srianand, N. Gupta, E. Momjian, P. Noterdaeme, et al.. H I 21-cm absorption survey of quasar-galaxy pairs: distribution of cold gas around z < 0.4 galaxies. Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2017, 465, pp.588-618. ⟨10.1093/mnras/stw2689⟩. ⟨insu-03666210⟩

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