The Mass Relations between Supermassive Black Holes and Their Host Galaxies at 1 < z < 2 with HST-WFC3

Abstract

Correlations between the mass of a supermassive black hole (SMBH) and the properties of its host galaxy (e.g., total stellar mass M * , luminosity L host ) suggest an evolutionary connection. A powerful test of a coevolution scenario is to measure the relations  BH – L host and  BH – M *  at high redshift and compare with local estimates. For this purpose, we acquired Hubble Space Telescope ( HST ) imaging with WFC3 of 32 X-ray-selected broad-line (type 1) active galactic nuclei at 1.2 <  z  < 1.7 in deep survey fields. By applying state-of-the-art tools to decompose the HST images including available ACS data, we measured the host galaxy luminosity and stellar mass along with other properties through the two-dimensional model fitting. The black hole mass (  BH ) was determined using the broad H α  line, detected in the near-infrared with the Subaru Fiber Multi-Object Spectrograph, which potentially minimizes systematic effects using other indicators. We find that the observed ratio of  BH to total M * is 2.7× larger at z  ∼ 1.5 than in the local universe, while the scatter is equivalent between the two epochs. A nonevolving mass ratio is consistent with the data at the 2 σ –3 σ confidence level when accounting for selection effects (estimated using two independent and complementary methods) and their uncertainties. The relationship between  BH and host galaxy total luminosity paints a similar picture. Therefore, our results cannot distinguish whether SMBHs and their total host stellar mass and luminosity proceed in lockstep or whether the growth of the former somewhat overshoots the latter, given the uncertainties. Based on a statistical estimate of the bulge-to-total mass fraction, the ratio  BH / M *,bulge  is offset from the local value by a factor of ∼7, which is significant even accounting for selection effects. Taken together, these observations are consistent with a scenario in which stellar mass is subsequently transferred from an angular momentum–supported component of the galaxy to a pressure-supported one through secular processes or minor mergers at a faster rate than mass accretion onto the SMBH.