A Study of Quasar Absorption-Line Systems With IRAS

July 1996 • 1996AJ....112...62T

Authors • Tanner, A. M. • Bechtold, Jill • Walker, C. E. • Black, John H. • Cutri, R. M.

Abstract • A survey of quasar absorbers was conducted using the Infrared Astronomical Satellite (IRAS) database. Quasars with known intervening absorption-line systems and broad absorption line (BAL) QSOs were selected primarily from Junkkarinen et aL [ApJ, 77, 203 (1991)]. Of the 570 quasars with IRAS data, 52 showed 3σ or better detections in at least one band in SCANPI analysis. The origin of the IRAS flux could be from the absorption-line systems, other galaxies, or the quasar itself. The spectral energy distributions for quasars detected in the absorption- line sample and BAL QSOs were found to be redder than those of two control samples which suggests that some of the IRAS flux may arise in dust associated with the intervening galaxies. IRAS SUPERSCANPI processing was carried out for 77 quasars with known Mg II absorption at z_abs_ < 1 to investigate the ensemble far-infrared properties of these objects. SUPERSCANPI processing evaluates the median flux for many different positions on the sky, resulting in an improvement in the effective sensitivity. A control sample consisting of objects with no Mg II absorption known at z_abs_ < 1 but with the same distribution of absolute V-magnitude, z_em_ and radio-loud fraction for the background quasars was also processed. The Mg II sample was detected at 3σ or better in all four IRAS bands with a significantly larger flux than the control sample at 60 microns and 100 microns. If this far-infrared emission is from the absorber galaxies, then the far-infrared luminosity of the composite Mg II absorber was found to be comparable to that of a starbursting galaxy, although such a high star-formation rate is inconsistent with the optical and near-infrared colors of low-redshift Mg II systems. Four of the quasars with individual IRAS detections have intervening galaxies identified with the Mg II absorption-lines. The spectral energy distributions of these galaxies imply far-infrared luminosities in excess of what Arp 220 would give at their redshifts. While all the external evidence suggests that the detection of far- infrared emission from the absorber sample may not be connected to the presence of the Mg II absorber, we discuss future observations which may help explain our results.

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Roc Cutri

IPAC Deputy Director