Conditions in the Z = 0.692 Absorber toward 3CR 286

Abstract

We present HST/FOS^1^ ultraviolet and ground-based optical spectra of the z = 0.692 21 cm absorption system in the QSO 3CR 286. The strength of the damped Lyα absorption implies an H I column density, N(H I)~2 x 10^21^ cm^-2^. We derive a high spin temperature for the H I gas, T_s_~> 10^3^ K, as has been found for other high-redshift 21 cm absorbing systems; at least 80% of the H I is hotter than 1200 K. Curve- of growth analysis yields Mg^+^ and Fe^+^ abundances which are ~1-2 dex below solar values; the Ca^+^ abundance is even lower implying some depletion onto dust grains. The H_2_ fraction is not high. We speculate that the high inferred T_s_, for the gas may reflect continuing active star formation at the 5-8 Gyr look-back time to the absorbing galaxy.