Discovery of z = 0.0912 and z = 0.2212 Damped Lyα Absorption-Line Systems Toward the Quasar OI 363: Limits on the Nature of Damped Lyα Galaxies

Abstract

The discovery of a z_abs=0.0912 damped Lyα absorption-line system in the Hubble Space Telescope Faint Object Spectrograph ultraviolet spectrum of the quasar OI 363 (0738+313) is reported. This is the lowest redshift quasar-damped Lyα system known. Its neutral hydrogen column density is N(H I) =1.5+/-0.2×10²¹ atoms cm^-2, which easily exceeds the classical criterion for damped Lyα of N(H I) >=2×10²⁰ atoms cm^-2. Remarkably, a z_abs=0.2212 damped system with N(H I) =7.9+/-1.4×10²⁰ atoms cm^-2 has also been discovered in the same spectrum.

In the past, the standard paradigm for damped Lyα systems has been that they arise in galactic or protogalactic H I disks with low impact parameters in luminous galaxies. However, WIYN imaging of the OI 363 field shows that none of the galaxies visible in the vicinity of the quasar is a luminous gas-rich spiral with low impact parameter, either at z=0.0912 or z=0.2212. Thus, these damped systems are among the clearest examples yet of cases that are inconsistent with the standard damped Lyα-H I-disk paradigm.

Based on data obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555, and on observations made with the KPNO WIYN telescope, National Optical Astronomy Observatories, operated by AURA, Inc., under cooperative agreement with the National Science Foundation.