THE NATURE OF INTERMEDIATE-REDSHIFT DAMPED LY-ALPHA ABSORBERS

We present HST/WFPC2 high-spatial resolution images in the R and B ban ds of the close environment of the sightlines to seven quasars which s pectra show either a damped Ly alpha absorption line, 21 cm absorption , or a very strong Mg II/Fe II absorption system at intermediate redsh ifts (0.4 less than or equal to z less than or equal to 1). Objects do wn to about 0.3 '', or 2.0 kpc at z = 0.6 (H-0 = 50 kms s(-1) Mpc(-1), q(0) = 0), and to a limiting magnitude m(702,lim) = 25.9 could be det ected for seven fields comprising eight absorbers (one at higher redsh ift z = 1.78 towards MC 1331 + 170) with high H I column densities of at least 1 x 10(20) cm(-2). In each case, a candidate absorber with ab solute magnitude M-B similar or equal to -19.0 or much brighter has be en detected. This small sample of gas-rich galaxies at intermediate re dshifts covers a wide range in morphological types. There are three sp iral galaxies of various sizes and luminosities (towards 3C 196, Q 120 9 + 107 and MC 1331 + 170), three compact objects (towards EX 0302 - 2 23, PKS 0454 + 039 and, at high redshift, MC 1331 + 170), and two amor phous, low surface brightness galaxies (towards PKS 1229 - 021 and 3C 286). In the fields around 3C 196, PKS 1229 - 021 and Q 1209 + 107, th ere is an excess of galaxies in the PC2 images, suggestive of the pres ence of a group of galaxies associated with the damped Ly alpha absorb er, or maybe with the quasar itself for the two z(e) less than or equa l to 1.0 cases. For 3C 196 and 3C 286, the quasar host galaxies have a lso tentatively been discovered. We do not detect any quasar multiple images, implying no large amount of dark matter around the damped Ly a lpha absorbers. This survey also led to the discovery of the first z s imilar or equal to 1.0 optical counterpart of a quasar radio jet (PKS 1229 - 021). As will be reported elsewhere (Boisse et al. 1996), spect roscopy with the HST-FOS of the strong Mg II/Fe II absorption systems confirms the validity of our selection criterion in predicting the exi stence of damped Ly alpha systems.