We present stellar velocity dispersion measurements in the host galaxies of 10 luminous quasars ( M _ { V } < - 23 ) using the Ca H & K lines in off-nuclear spectra .
We combine these data with effective radii and magnitudes from the literature to place the host galaxies on the Fundamental Plane ( FP ) where their properties are compared to other types of galaxies .
We find that the radio-loud ( RL ) QSO hosts have similar properties to massive elliptical galaxies , while the radio-quiet ( RQ ) hosts are more similar to intermediate mass galaxies .
The RL hosts lie at the upper extreme of the FP due to their large velocity dispersions ( \langle \sigma _ { * } \rangle = 321 km s ^ { -1 } ) , low surface brightness ( \langle \mu _ { e } ( r ) \rangle = 20.8 mag arcsec ^ { -2 } ) , and large effective radii ( \langle R _ { e } \rangle = 11.4 kpc ) , and have \langle M _ { * } \rangle = 1.5 x 10 ^ { 12 } M _ { \sun } and \langle M / L \rangle = 12.4 .
In contrast , properties of the RQ hosts are \langle \sigma _ { * } \rangle = 241 km s ^ { -1 } , \langle M _ { * } \rangle \sim 4.4 x 10 ^ { 11 } M _ { \sun } , and M/L \sim 5.3 .
The distinction between these galaxies occurs at \sigma _ { * } \sim 300 km s ^ { -1 } , R _ { e } \sim 6 kpc , and corresponding M _ { * } \sim 5.9 \pm 3.5 x 10 ^ { 11 } M _ { \sun } .
Our data support previous results that PG QSOs are related to gas-rich galaxy mergers that form intermediate-mass galaxies , while RL QSOs reside in massive early-type galaxies , most of which also show signs of recent mergers or interactions .
Most previous work has drawn these conclusions by using estimates of the black hole mass and inferring host galaxy properties from that , while here we have relied purely on directly measured host galaxy properties .