SDSS J094533.99+100950.1 - the remarkable weak emission line quasar

Abstract

Weak emission line quasars are a rare and puzzling group of objects. In this paper, we present one more object of this class found in the Sloan Digital Sky Survey (SDSS). The quasar SDSS J094533.99+100950.1, lying at z= 1.66, has practically no C iv emission line, a red continuum very similar to the second steepest of the quasar composite spectra of Richards et al., is not strongly affected by absorption and the Mg ii line, although relatively weak, is strong enough to measure the black hole mass. The Eddington ratio in this object is about 0.45, and the line properties are not consistent with the trends expected at high accretion rates. We propose that the most probable explanation of the line properties in this object, and perhaps in all weak emission line quasars, is that the quasar activity has just started. A disc wind is freshly launched so the low ionization lines which form close to the disc surface are already observed but the wind has not yet reached the regions where high ionization lines or narrow line components are formed. The relatively high occurrence of such a phenomenon may additionally indicate that the quasar active phase consists of several subphases, each starting with a fresh build-up of the broad-line region.