Host galaxies of hard X-ray-selected type 2 active galactic nuclei at intermediate redshifts

We study properties of the host galaxies of 15 hard X-ray-selected type 2 active galactic nuclei (AGNs) at intermediate redshifts (0.05 < z < 0.6) detected in ASCA surveys. The absorption-corrected hard X-ray luminosities L_{2-10 keV} range from 10⁴² to 10⁴⁵ ergs s ^-1. We took the A-band image of these AGNs with the University of Hawaii 2.2 m telescope. Thanks to the intrinsic obscuration of nuclear light, we can decompose the galaxies with a spheroid component and a disk component. The resulting spheroid luminosities correlate with L_{2-10 keV}; higher (lower) X-ray luminosity AGNs tend to reside in more luminous (less luminous) spheroids. It is also found that the hosts of luminous AGNs show a large spheroid-to-disk luminosity ratio (∼1), while those of less luminous AGNs spread between 0 and 1. The correlation between L_{2-10 keV} and spheroid luminosity indicates a relation between the mass of a supermassive black hole (SMBH) and the spheroid luminosity (BS relation) at intermediate redshifts. The BS relation agrees with that in the local universe if an Eddington ratio of 0.24 is adopted, which is a mean value determined from our ASCA type 1 AGN sample at similar redshifts through the broad line width and continuum luminosity. The present study demonstrates the effectiveness of using type 2 AGNs at high redshifts to study their host properties.