Discovery of an Ultra-Steep Spectrum, Highly Polarized Red Quasar at z = 1.462

Abstract

We report the discovery of WN J0717+4611, a highly polarized red quasar at z=1.462, selected from a sample of faint (S_{1.4GHz} > 10 mJy) ultra steep spectrum (alpha < -1.3) radio sources. VLA observations at 4.85 GHz show that the radio source is dominated by a 21 mJy core. Using the Keck telescopes, we obtained spectra with a combined wavelength range covering 4000 Angstroms to 1.6 microns, and spectropolarimetric observations between 4000 Angstroms and 9000 Angstroms. We identify WN J0717+4611 as a quasar based on broad emission of Mg II 2799 (FWHM ~ 11,000 km/s), a stellar R_S band Lick image and the high luminosity of the object (M_B = -24.2). The optical linear polarization is wavelength-independent at 15% in both the continuum and the emission lines, with the polarization angle orthogonal to the radio jet axis. We argue that the polarization mechanism is scattering of quasar light by surrounding small dust grains or electrons. WN J0717+4611 appears highly reddened for a core-dominated quasar.