Radio line and continuum observations of quasar-galaxy pairs and the origin of low reshift quasar absorption line systems

There are a number of known quasars for which our line of sight to the high redshift quasar passes within a few Holmberg radii of a low redshift galaxy. In a few of these cases, spectra of the quasar reveal absorption by gas associated with the low redshift galaxy. A number of these pairs imply absorption by gas which lies well outside the optical disk of the associated galaxy, leading to models of galaxies with 'halos' or 'disks' of gas extending to large radii. The authors present observations of 4 such pairs. In three of the four cases, they find that the associated galaxy is highly disturbed, typically due to a gravitational interaction with a companion galaxy, while in the fourth case the absorption can be explained by clouds in the optical disk of the associated galaxy. They are led to an alternative hypothesis concerning the origin of the low redshift absorption line systems: the absorption is by gas clouds which have been gravitationally stripped from the associated galaxy. These galaxies are rapidly evolving, and should not be used as examples of absorption by clouds in halos of field spirals. The authors conclude by considering the role extended gas in interacting systems plays in the origin of higher redshift quasar absorption line systems

The Diverse Infrared Properties of a Complete Sample of Star-Forming Dwarf Galaxies

We present mid-infrared Spitzer Space Telescope observations of a complete sample of star-forming dwarf galaxies selected from the KPNO International Spectroscopic Survey. The galaxies span a wide range in mid-infrared properties. Contrary to expectations, some of the galaxies emit strongly at 8 micron indicating the presence of hot dust and/or PAHs. The ratio of this mid-infrared dust emission to the stellar emission is compared with the galaxies' luminosity, star-formation rate, metallicity, and optical reddening. We find that the strength of the 8.0 micron dust emission to the stellar emission ratio is more strongly correlated with the star-formation rate than it is with the metallicity or the optical reddening in these systems. Nonetheless, there is a correlation between the 8.0 micron luminosity and metallicity. The slope of this luminosity-metallicity correlation is shallower than corresponding ones in the B-band and 3.6 micron. The precise nature of the 8.0 micron emission seen in these galaxies (i.e., PAH versus hot dust or some combination of the two) will require future study, including deep mid-IR spectroscopy.Comment: 14 pages, accepted Ap