HUBBLE SPACE TELESCOPE NEAR-INFRARED SNAPSHOT SURVEY OF 3CR RADIO SOURCE COUNTERPARTS. III. RADIO GALAXIES AND QUASARS IN CONTEXT

We compare the near-infrared (NIR) H-band photometric and morphological properties of low-z (z < 0.3) 3CR radio galaxies with samples of BL Lac objects and quasar host galaxies, merger remnants, quiescent elliptical galaxies, and brightest cluster galaxies drawn from the literature. In general, the 3CR host galaxies are consistent with luminous (∼L *) elliptical galaxies. The vast majority of FR II's (∼80%) occupy the most massive ellipticals and form a homogeneous population that is comparable to the population of radio-loud quasar (RLQ) host galaxies in the literature. However, a significant minority (∼20%) of the 3CR FR II's appears under-luminous with respect to quasar host galaxies. All FR II objects in this faint tail are either unusually red, or appear to be the brightest objects within a group. We discuss the apparent differences between the radio galaxy and RLQ host galaxy populations. RLQs appear to require ∼>1011 Msun host galaxies (and ∼109 Msun black holes), whereas radio galaxies and radio-quiet quasars can exist in galaxies down to ∼3 x 1010 Msun. This may be due to biases in the measured quasar host galaxy luminosities or populations studied, or due to a genuine difference in host galaxy. If due to a genuine difference, it would support the idea that radio and optical active galactic nuclei are two separate populations with a significant overlap.