New blazars discovered by polarimetry

Abstract

We have discovered 31 blazars and confirmed five others as part of a program of optical polarimetry of a complete sample of radio sources. This increases the number of known polarized radio sources by 40%. Twenty-five blazars were measured more than once, and strong variability in flux density is seen in 10 objects. The level of interstellar polarization was checked with observations of several faint stars near the position of each radio source. Some of the new blazars have large redshifts and are optically faint. There are equal numbers of objects with strong and weak emission lines, and the weak-lined objects have the largest ratios of optical to radio power. We present tentative evidence for an unprecedented pair of polarized objects, only one of which is a radio source. In a complete radio sample selected at 5 GHz, 40% of the optical counterparts with stellar images are highly polarized. This fraction increases with increasing dominance of a compact radio component.