A submillimeter survey of gravitationally lensed quasars

Submillimeter (and in some cases millimeter) wavelength continuum measurements are presented for a sample of 40 active galactic nuclei ( probably all quasars) lensed by foreground galaxies. The object of this study is to use the lensing boost, anywhere from similar to3 to 20 times, to detect dust emission from more typical active galactic nuclei (AGNs) than the extremely luminous ones currently accessible without lensing. The sources are a mix of radio-loud and radio-quiet quasars, and after correction for synchrotron radiation ( in the few cases where necessary), 23 of the 40 ( 58%) are detected in dust emission at 850 l m; 11 are also detected at 450 mum. Dust luminosities and masses are derived after correction for lensing magnification, and luminosities are plotted against redshift from z = 1 to z = 4.4, the redshift range of the sample. The main conclusions are (1) monochromatic submillimeter luminosities of quasars are, on average, only a few times greater than those of local IRAS galaxies; (2) radio-quiet and radio-loud quasars do not differ significantly in their dust luminosity; (3) mean dust luminosities of quasars and radio galaxies over the same redshift range are comparable; and (4) quasars and radio galaxies alike show evidence for more luminous and massive dust sources toward higher redshift, consistent with an early epoch of formation and possibly indicating that the percentage of obscured AGNs increases with redshift.