Host Galaxies of the High-redshift AGNs in the GOODS Fields

Abstract

The star-formation rates and the stellar masses of the host galaxies of AGNs at high-redshifts are keys to understanding the evolution of the relation between the mass of the spheroidal component of a galaxy and the mass of its central black hole. We investigate the host galaxies of 31 AGNs with spectroscopic redshifts between 2 and 4 found in the deep Chandra surveys of the GOODS fields with the ACS images. The sample can be divided into 17 ``extended&#39;&#39; AGNs and 14 ``compact&#39;&#39; AGNs based on the concentration parameter defined as the difference between the aperture magnitudes with 0.07&#34; and 0.25&#34; diameter. We derive upper limits of the UV luminosities of the host galaxies of the ``compact&#39;&#39; AGN sample, and upper and lower limits of the UV luminosities of the host galaxies of the ``extended&#39;&#39; AGN sample.These limits are consistent with the knee of the luminosity function of the Lyman Break Galaxies (LBGs) at z=3, suggesting moderate star-formation rates, less than 40 Msolar/yr, in the host galaxies of the AGNs at 2<z_sp<4 without correcting the dust extinction. By combining the limits of the UV luminosities with the observed K-band magnitudes for the ``extended&#39;&#39; AGNs, we derive the upper and lower limits of the stellar masses of their host galaxies. The derived upper limits on the stellar masses range from 10^10 Msolar to 10^12 Msolar. The upper limits imply that the Mbulge-MBH relation of the high-redshift AGNs is different from that of the galaxies in the nearby universe or the average Eddington ratio of the high-redshift AGNs is higher than that of low-redshift AGNs with lower-luminosity.