Colors of Active Galactic Nucleus Host Galaxies at 0.5 < z < 1.1 from the GEMS Survey

Abstract

We present the results from a study of the host galaxies of 15 optically selected active galactic nuclei (AGNs) with 0.5 < z < 1.1 from the Galaxy Evolution from Morphology and SEDs project (GEMS). GEMS is a Hubble Space Telescope imaging survey of a ∼28′ × 28′ contiguous field centered on the Chandra Deep Field-South in the F606W and F850LP filter bands. It incorporates the spectral energy distributions and redshifts of ∼ 10,000 objects, obtained by the COMBO-17 project. We have detected the host galaxies of all 15 AGNs in the F850LP band (and 13 of 15 in the F606W band), recovering their fluxes, morphologies, and structural parameters. We find that 80% of the host galaxies have early-type (bulge-dominated) morphologies, while the rest have structures characteristic of late-type (disk-dominated) galaxies. We find that 25% of the early types and 30% of the late types exhibit disturbances consistent with galaxy interactions. The hosts show a wide range of colors, from those of red-sequence galaxies to blue colors consistent with ongoing star formation. Roughly 70% of the morphologically early-type hosts have rest-frame blue colors, a much larger fraction than those typical of nonactive morphologically early-type galaxies in this redshift and luminosity range. Yet, we find that the early-type hosts are structurally similar to red-seque nce elliptical galaxies, inasmuch as they follow an absolute magnitude versus half-light size correlation that is consistent with the mean relation for early-type galaxies at similar redshifts.