The Radio Galaxy 3C 265 Contains a Hidden Quasar Nucleus

Abstract

We report the discovery of broad MgII emission from the high redshift radio galaxy 3C265 (z=0.81). We detect the broad line in the nuclear spectrum and in the spatially extended galaxian component, both near the nucleus and in the spectrum of an off-nuclear knot located 31 kpc south east of the nucleus of the galaxy. These data provide strong support for the simplest form of the unification hypothesis, that radio galaxies are quasars whose optical radiation is directed in the plane of the sky rather than into our line of sight. These data also strongly support the scattering model for the alignment of the UV continuum emission with the radio axis. In 3C265, if the axis of the anisotropically emitted UV continuum radiation is identified with the major axis of the radio source, then the observed rest frame UV continuum emission implies that the opening angle of the radiation cone is large (half angle approximately 45 degrees). We also derive a mass estimate of 8x10^{10} Msun for the central region of 3C265 from its rotation curve. The implied mass-to-light ratio is low (M/L is roughly 2), and suggests that a significant fraction of the rest frame UV continuum emission from this galaxy is dominated by reprocessed radiation from the buried AGN. Finally, we detect the CaII\lambda3933 K line in absorption in the integrated spectrum of 3C265. This provides direct spectroscopic evidence for the existence of stars in a high redshift radio galaxy.