Type II Quasars from the Sloan Digital Sky Survey. V. Imaging Host Galaxies with the Hubble Space Telescope

Abstract

Type II quasars are luminous active galactic nuclei (AGNs) whose centers are obscured by large amounts of gas and dust. In this paper we present three-band Hubble Space Telescope images of nine type II quasars with redshifts 0.2 MB>-26, but optical obscuration allows their host galaxies to be studied unencumbered by bright nuclei. Each object has been imaged in three continuum filters (``UV,'' ``blue,'' and ``yellow'') placed between the strong emission lines. The spectacular, high-quality images reveal a wealth of details about the structure of the host galaxies and their environments. Six of the nine galaxies in the sample are elliptical galaxies with de Vaucouleurs light profiles, one object has a well-defined disk component, and the remaining two have marginal disks. Stellar populations of type II quasar hosts are more luminous (by a median of 0.3-0.7 mag, depending on the wavelength) and bluer (by about 0.4 mag) than are M* galaxies at the same redshift. When smooth fits to stellar light are subtracted from the images, we find both positive and negative residuals that become more prominent toward shorter wavelengths. We argue that the negative residuals are due to kiloparsec-scale dust obscuration, while most positive residuals are due to the light from the nucleus scattered off interstellar material in the host galaxy. Scattered light makes a significant contribution to the broadband continuum emission and can be the dominant component of the extended emission in the UV in extreme cases. This paper is dedicated to the memory of John Norris Bahcall, a pioneer in the study of quasar host galaxies. The observations reported here were obtained with the NASA/ESA Hubble Space Telescope and at the MMT Observatory, a facility operated jointly by the Smithsonian Institution and the University of Arizona. Public access time is available at the MMT Observatory through an agreement with the National Science Foundation.