The sloan digital sky survey reverberation mapping project: The M_BH-host relations at 0.2 ≲ z ≲ 0.6 from reverberation mapping and hubble space telescope imaging

We present the results of a pilot Hubble Space Telescope (HST) imaging study of the host galaxies of ten quasars from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project. Probing more than an order of magnitude in black hole (BH) and stellar masses, our sample is the first statistical sample to study the BH-host correlations beyond z > 0.3 with reliable BH masses from reverberation mapping rather than from single-epoch spectroscopy. We perform image decomposition in two HST bands (UVIS-F606W and IR-F110W) to measure host colors and estimate stellar masses using empirical relations between broadband colors and the mass-to-light ratio. The stellar masses of our targets are mostly dominated by a bulge component. The BH masses and stellar masses of our sample broadly follow the same correlations found for local RM active galactic nuclei and quiescent bulge-dominant galaxies, with no strong evidence of evolution in the M_BH -M_*,bulge relation to z ∼ 0.6. We further compare the host light fraction from HST imaging decomposition to that estimated from spectral decomposition. We find a good correlation between the host fractions derived with both methods. However, the host fraction derived from spectral decomposition is systematically smaller than that from imaging decomposition by ∼30%, indicating different systematics in both approaches. This study paves the way for upcoming more ambitious host galaxy studies of quasars with direct RM-based BH masses at high redshift.