HI 21-cm absorption at z~ 3.39 towards PKS 0201+ 113

Kanekar, N. ; Chengalur, J. N. ; Lane, W. M. (2007) HI 21-cm absorption at z~ 3.39 towards PKS 0201+ 113 Monthly Notices of the Royal Astronomical Society, 375 (4). pp. 1528-1536. ISSN 0035-8711

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Official URL: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-...

Related URL: http://dx.doi.org/10.1111/j.1365-2966.2007.11430.x


We report the Giant Metrewave Radio Telescope detection of HI 21-cm absorption from the z~ 3.39 damped Lyman absorber (DLA) towards PKS 0201+113, the highest redshift at which 21-cm absorption has been detected in a DLA. The absorption is spread over ˜115 km s−1 and has two components, at z= 3.387 144(17) and z= 3.386 141 (45). The stronger component has a redshift and velocity width in agreement with the tentative detection of Briggs, Brinks & Wolfe, but a significantly lower optical depth. The core size and DLA covering factor are estimated to be ≲100 pc and f~ 0.69, respectively, from a Very Long Baseline Array 328-MHz image. If one makes the conventional assumption that the HI column densities towards the optical and radio cores are the same, this optical depth corresponds to a spin temperature of Ts~[(955 ± 160) × (f/0.69)] K. However, this assumption may not be correct, given that no metal-line absorption is seen at the redshift of the stronger 21-cm component, indicating that this component does not arise along the line of sight to the optical quasi-stellar object (QSO), and that there is structure in the 21-cm absorbing gas on scales smaller than the size of the radio core. We model the 21-cm absorbing gas as having a two-phase structure with cold dense gas randomly distributed within a diffuse envelope of warm gas. For such a model, our radio data indicate that, even if the optical QSO lies along a line of sight with a fortuitously high (˜50 per cent) cold gas fraction, the average cold gas fraction is low, ≲17 per cent, when averaged over the spatial extent of the radio core. Finally, the large mismatch between peak 21-cm and optical redshifts and the complexity of both profiles makes it unlikely that the z~ 3.39 DLA will be useful in tests of fundamental constant evolution.

Item Type:Article
Source:Copyright of this article belongs to John Wiley and Sons.
Keywords:Galaxies: Evolution; Galaxies: ISM; Radio Lines: Galaxies
ID Code:63538
Deposited On:29 Sep 2011 04:08
Last Modified:29 Sep 2011 04:08

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