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Astron. Astrophys. 321, 733-748 (1997)

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The nature of intermediate-redshift damped Ly [FORMULA] absorbers *

V. Le Brun 1, J. Bergeron 2, 3, P. Boissé 4 and J.M. Deharveng 1

1 Laboratoire d'Astronomie Spatiale du C.N.R.S., B.P. 8, F-13376 Marseille Cedex 12, France (vlebrun@astrsp-mrs.fr, jmd@astrsp-mrs.fr)
2 European Southern Observatory, Karl-Schwarzschild-Straße 2., D-85748 Garching b. M"unchen, Germany (jbergero@eso.org)
3 Institut d'Astrophysique de Paris, CNRS, 98bis boulevard Arago, F-75014 Paris, France
4 Ecole Normale Supérieure, 24 rue Lhomond, F-75005 Paris, France (boisse@ensapa.ens.fr)

Received 24 May 1996 / Accepted 23 October 1996

Abstract

We present HST/WFPC2 high-spatial resolution images in the R and B bands of the close environment of the sightlines to seven quasars which spectra show either a damped Ly [FORMULA] absorption line, 21 cm absorption, or a very strong Mg II /Fe II absorption system at intermediate redshifts ([FORMULA]). Objects down to about [FORMULA], or 2.0 kpc at [FORMULA] ([FORMULA]  kms s-1  Mpc-1, [FORMULA]), and to a limiting magnitude [FORMULA] could be detected for seven fields comprising eight absorbers (one at higher redshift z = 1.78 towards MC 1331+170) with high H I column densities of at least [FORMULA]  cm-2.

In each case, a candidate absorber with absolute magnitude [FORMULA] or much brighter has been detected. This small sample of gas-rich galaxies at intermediate redshifts covers a wide range in morphological types. There are three spiral galaxies of various sizes and luminosities (towards 3C 196, Q 1209+107 and MC 1331+170), three compact objects (towards EX 0302-223, PKS 0454+039 and, at high redshift, MC 1331+170), and two amorphous, low surface brightness galaxies (towards PKS 1229-021 and 3C 286). In the fields around 3C 196, PKS 1229-021 and Q 1209+107, there is an excess of galaxies in the PC2 images, suggestive of the presence of a group of galaxies associated with the damped Ly [FORMULA] absorber, or maybe with the quasar itself for the two [FORMULA] 1.0 cases. For 3C 196 and 3C 286, the quasar host galaxies have also tentatively been discovered. We do not detect any quasar multiple images, implying no large amount of dark matter around the damped Ly [FORMULA] absorbers.

This survey also led to the discovery of the first [FORMULA] 1.0 optical counterpart of a quasar radio jet (PKS 1229-021).

As will be reported elsewhere (Boissé et al. 1996), spectroscopy with the HST-FOS of the strong Mg II /Fe II absorption systems confirms the validity of our selection criterion in predicting the existence of damped Ly [FORMULA] systems.

Key words: quasar: absorption lines – galaxies: ISM – galaxies: halos

* Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555

Send offprint requests to: V. Le Brun

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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