3C 48: Stellar Populations and the Kinematics of Stars and Gas in the Host Galaxy

Abstract

We present deep Keck LRIS spectroscopy of the host galaxy of 3C 48. Our observations at various slit positions sample the different luminous components near the quasar, including the apparent tidal tail to the northwest and several strong emission line regions. By fitting Bruzual & Charlot population synthesis models to our spectra, we obtain ages for the most recent major episodes of star formation in various parts of the host galaxy covered by our slits. There is vigorous current star formation in regions just northeast and southeast of the quasar and post-starburst regions with ages up to ~108 yr in other parts of the host galaxy, but most of the northwest tidal tail shows no sign of significant recent star formation. We use these model fits, together with the kinematics of the stars and gas, to outline a plausible evolutionary history for the host galaxy, its recent starburst activity, the triggering of the quasar, and the interaction of the radio jet with the ambient gas. There is strong evidence that the 3C 48 host is an ongoing merger, and that it is probably near the peak of its starburst activity. Nevertheless, the quasar itself seems to suffer little extinction, perhaps because we are viewing it along a particularly favorable line of sight.