Massive Star-Forming Host Galaxies of Quasars on Sloan Digital Sky
  Survey Stripe 82
  The stellar properties of about 800 galaxies hosting optically luminous,
unobscured quasars at z < 0.6 are analyzed. Deep co-added Sloan Digital Sky
Survey (SDSS) images of the quasars on Stripe 82 are decomposed into nucleus
and host galaxy using point spread function and Sersic models. The systematic
errors in the measured galaxy absolute magnitudes and colors are estimated to
be less than 0.5 mag and 0.1 mag, respectively, with simulated quasar images.
The effect of quasar light scattered by the interstellar medium is also
carefully addressed. The measured quasar-to-galaxy ratio in total flux
decreases toward longer wavelengths, from ~8 in the u band to ~1 in the i and z
bands. We find that the SDSS quasars are hosted exclusively by massive galaxies
(stellar mass Mstar > 10^{10} Msun), which is consistent with previous results
for less luminous narrow-line (obscured) active galactic nuclei (AGNs). The
quasar hosts are very blue and almost absent on the red sequence, showing stark
contrast to the color-magnitude distribution of normal galaxies. The fact that
more powerful AGNs reside in galaxies with higher star-formation efficiency may
indicate that negative AGN feedback, if it exists, is not concurrent with the
most luminous phase of AGNs. We also find positive correlation between the mass
of supermassive black holes (SMBHs; Mbh) and host stellar mass, but the Mbh -
Mstar relation is offset toward large Mbh or small Mstar compared to the local
relation. While this could indicate that SMBHs grow earlier than do their host
galaxies, such an argument is not conclusive, as the effect may be dominated by
observational biases.
