Co-evolution of supermassive black hole and host galaxy from z ∼ 1 to z = 0

Abstract

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 (Mbulge) and star formation rates (SFRs) of the bulge components by spectral energy distribution fitting. The derived Mbulge ranges over 109-1011 M ⊙, and the estimated SFR is 0.01-100 M⊙ yr -1. 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-1, respectively. For luminous AGNs, the estimated M•/Mbulge ratio is ∼4 × 10-4 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•/Mbulge 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•/Mbulge 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. © 2009. The American Astronomical Society.