The Extent and Content of Low Ionization Gas in Galaxies

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Session 78 -- QSOs and Gravitational Lenses
Oral presentation, Thursday, 2:30-4:00, Durham Room

[78.01] The Extent and Content of Low Ionization Gas in Galaxies

D. S. Womble (CASS/UCSD and Caltech)

The fortuitous juxtaposition of QSOs and galaxies provides unique opportunities to probe the extent and content of gas in the foreground galaxies through evaluation of the incidence and strength of absorption lines in the spectra of the background QSOs. We present optical, spectroscopic observations of a new sample of nine close QSO-galaxy ``pairs''; these objects were selected with more strict limitations on the QSO-galaxy impact parameters than in previous studies. For a select subset of these galaxies, we present VLA images of the H\thinspace I 21\thinspace cm emission. These observations are combined with deep optical images and far-infrared fluxes of the galaxies to assess and interpret morphological and environmental conditions which may influence the absorption status. Using these new data in combination with the existing measurements for all pairs with similar impact parameters, we form a ``complete'' sample of 22 close pairs from which we draw a number of global conclusions.

Naive assumptions regarding a direct correspondence between the incidence and strength of Ca\thinspace II absorption and the impact parameters are invalid for these data. There does not appear to be a sharp impact parameter limit beyond which Ca\thinspace II absorption is never detected, nor is there a minimum separation below which absorption is always detected. Limits on the relative abundance of Ca\thinspace II and H\thinspace I indicate that the QSO-galaxy pair absorption systems have gas-phase abundances of calcium which are larger than in the majority of Galactic halo sightlines. We tentatively find that the absorbing galaxies are more luminous in the optical and far-infrared than the non-absorbers. Combined with a qualitative assessment of the galaxy morphologies and environments, we find that these results are consistent with the absorbers being characteristically more active than the non-absorbers. Tidal interactions and active star-formation play important and perhaps crucial roles in the origin of the absorbing gas. We interpret these results in the context of calcium depletion, and we briefly compare the inferred properties with those seen in higher redshift QSO absorption systems.

Thursday program listing