2009ApJ...696.1051K

Stellar masses of bulges in hosts of active galactic nuclei (AGNs) and black hole masses in the AGNs are derived at z = 0.5-1.15 to study evolution of the black hole-to-bulge mass relation. In order to derive bulge stellar masses, we use a sample of type-2 AGNs to avoid the bright nuclear light. 34 type-2 AGNs are selected from the spectroscopically identified X-ray sources in the Chandra Deep Field South. We use optical images from the Hubble Space Telescope, and near- and mid-infrared photometry from the Very Large Telescope and the Spitzer Space Telescope. The bulge components are derived by fitting the two-dimensional surface brightness model consisting of a bulge and a disk component to the optical images. We derive stellar masses (M_bulge) and star formation rates (SFRs) of the bulge components by spectral energy distribution fitting. The derived M_bulge ranges over 10⁹-10¹¹ M_☉, and the estimated SFR is 0.01-100 M_☉/yr. Masses of supermassive black holes (SMBHs; M_•) and black hole accretion rates (BHARs) are estimated with the absorption-corrected X-ray luminosities in the 2-10 keV band under an assumption of the constant Eddington ratio of 0.1 and the constant energy conversion factor of 0.1. Resulting black hole masses and BHARs range over 10^5.5-10⁸ M_☉ and 0.001-1 M_☉/yr, respectively. For luminous AGNs, the estimated M_•/M_bulge ratio is ∼4x10^–4 in the median, which is lower than that for local galaxies and for type-2 AGNs at z ∼ 0.2. However, these differences are within uncertainty and are not significant. This can imply that SMBHs and their host galaxies are evolving almost holding the constant M_•/M_bulge ratio from z ∼ 1.0 to 0 in a cosmological timescale. Meanwhile, the estimated BHAR/SFR ratio is about 60 times larger than the M_•/M_bulge ratio in the median value. This indicates that growths of SMBHs and their host bulges do not proceed simultaneously in a shorter timescale such as an AGN phase.