H i 21-cm absorption at z∼ 3.39 towards PKS 0201+113 |
| |
| Authors: | N Kanekar J N Chengalur W M Lane |
| |
| Institution: | National Radio Astronomy Observatory, 1003 Lopezville Road, Socorro, NM 87801, USA;National Centre for Radio Astrophysics, Ganeshkhind, Pune 411007, India;Australia Telescope National Facility, CSIRO, Epping, NSW 1710, Australia;Naval Research Laboratory, Code 7213, 4555 Overlook Avenue SW, Washington, DC 20375, USA |
| |
| Abstract: | We report the Giant Metrewave Radio Telescope detection of H i 21-cm absorption from the z ～ 3.39 damped Lyman α 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 H i column densities towards the optical and radio cores are the same, this optical depth corresponds to a spin temperature of T s～(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. |
| |
| Keywords: | galaxies: evolution galaxies: ISM radio lines: galaxies |
|
|
