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Issue A&A
Volume 412, Number 2, December III 2003
Page(s) L29 - L32
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20031676



A&A 412, L29-L32 (2003)
DOI: 10.1051/0004-6361:20031676

Letter

HI absorption in a gravitational lens at z ~ 0.7645

N. Kanekar1 and F. H. Briggs2

1  Kapteyn Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
2  RSAA, The Australian National University, Mount Stromlo Observatory, Cotter Road, ACT 2611, Australia

(Received 7 October 2003 / Accepted 31 October 2003)

Abstract
We have used the Westerbork Synthesis Radio Telescope to detect HI 21 cm absorption at $z \sim 0.7645$ in the gravitational lens system towards PMN J0134-0931. The 21 cm profile has two broad components, with peak optical depths of $0.047 \pm 0.007$ and $0.039 \pm 0.007$, at heliocentric redshifts $0.76470 \pm 0.00006$ and $0.76348 \pm 0.00006$, respectively. The redshift of the stronger component matches that of CaII H and K absorption detected earlier. The absorption has a total velocity width of ~ 500 km s -1 (between nulls) and an equivalent width of $7.1 \pm 0.08$ km s -1. This would imply a total HI column density of $2.6 \pm 0.3 \times 10^{21}$ cm -2, for a spin temperature of 200 K and a covering factor of unity. The high estimated HI column density is consistent with the presence of large amounts of dust at the lens redshift; the intervening dust could be responsible for the extremely red colour of the background quasar.


Key words: galaxies: individual: PMN J0134-0931 -- gravitational lensing -- radio lines -- ISM

Offprint request: N. Kanekar, nissim@astro.rug.nl

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© ESO 2003


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