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We have obtained a UV spectrum of PKS 1229--021 with the FOS/G160L and an R band image using WFPC II, as part of a program to identify the galaxies responsible for moderate redshift 21~cm absorption in quasar spectra. The wide field camera image clearly shows a luminous galaxy centered within 1" of the QSO. This galaxy has also been detected by Steidel et al. (1994). The spectrum shows a damped Ly$\alpha$\ line at the 21~cm redshift, $z=0.395$, indicating a column density in neutral hydrogen of approximately $2 \times 10^{20}$\ cm$^{-2}$. Measurement of the damped Ly$\alpha$\ line required a spectral fit incorporating several Lyman limit systems which are confirmed by the detection of Mg II absorption in new optical spectra. In contrast with measurements in higher redshift damped Ly$\alpha$\ systems, comparison with the 21~cm absorption line (Brown and Spencer 1979) suggests a low spin temperature similar to that seen in Galactic clouds. There is considerable uncertainty, however, because PKS 1229--021 is an extended radio source.
These observations are part of the GHRS GTO program and are supported by NASA grant NAG 5--1858.
