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We report the results from a deep HST NICMOS H-band imaging survey of 28 z <0.3 QSOs from the Palomar-Green (PG) sample. This program is part of QUEST(Quasar / ULIRG Evolution STudy) and complements a similar set of data on 26highly-nucleated ULIRGs presented in Paper I. Our analysis indicates that thefraction of QSOs with elliptical hosts is higher among QSOs with undetectedfar-infrared (FIR) emission, small infrared excess, and luminous hosts. Thehosts of FIR-faint QSOs show a tendency to have less pronounced merger-inducedmorphological anomalies and larger QSO-to-host luminosity ratios on averagethan the hosts of FIR-bright QSOs, consistent with late-merger evolution fromFIR-bright to FIR-faint QSOs. The spheroid sizes and total host luminosities ofthe radio-quiet PG QSOs in our sample are statistically indistinguishable fromthe ULIRG hosts presented in Paper I, while those of radio-loud PG QSOs aresystematically larger and more luminous. ULIRGs and PG QSOs with ellipticalhosts fall near, but not exactly on, the fundamental plane of inactivespheroids. We confirm the systematic trend noted in Paper I for objects withsmall (< 2 kpc) spheroids to be up to ~1 mag. brighter than inactive spheroids.The host colors and wavelength dependence of their sizes support the idea thatthese deviations are due at least in part to non-nuclear star formation.However, the amplitudes of these deviations does not depend on host R-H colors.Taken at face value (i.e., no correction for extinction or the presence of ayoung stellar population), the H-band spheroid-host luminosities imply BHmasses ~5 -- 200 x 10^7 M_sun and sub-Eddington mass accretion rates for bothQSOs and ULIRGs. These results are compared with published BH mass estimatesderived from other methods. (abridged)

A Deep HST H-Band Imaging Survey of Massive Gas-Rich Mergers. II. The QUEST PG QSOs