A 21 centimeter absorber identified with a spiral galaxy: Hubble space telescope faint object spectrograph and wide-field camera observations of 3CR 196

We present imaging and spectroscopy of the quasar 3CR 196 (z(e) = 0.871), which has 21 cm and optical absorption at z(a) = 0.437. We observed the region of Ly alpha absorption in 3CR 196 at z(a) = 0.437 with the Faint Object Spectrograph on the Hubble Space Telescope. This region of the spectrum is complicated because of the presence of a Lyman limit and strong lines from a z(a) approximate to z(e) system. We conclude that there is Ly alpha absorption with an H I column density greater than 2.7 x 10(19) cm(-2) and most probably 1.5 x 10(20) cm(-2). Based on the existence of the high H I column density along both the optical and radio lines of sight, separated by more than 15 kpc, we conclude that the Ly alpha absorption must arise in a system comparable in size to the gaseous disks of spiral galaxies. A barred spiral galaxy, previously reported as a diffuse object in the recent work of Boisse & Boulade, can be seen near the quasar in an image taken at 0.'' 1 resolution with the Wide Field Planetary Camera 2 on the HST. If this galaxy is at the absorption redshift, the luminosity is approximately L*, and any H I disk should extend in front of the optical quasar and radio lobes of 3CR 196, giving rise to both the Ly alpha and 21 cm absorption. In the z(a) approximate to z(e) system we detect Lyman lines and the Lyman limit, as well as high ion absorption lines of C III, N V, S VI, and O VI. This absorption probably only partially covers the emission-line region. The ionization parameter is approximately 0.1. Conditions in this region may be similar to those in broad absorption line QSOs.