In Joe Hennawi's (MPIA) group meeting today, lots of discussion broke out about quasars, unification, viewing angles, dust obscuration, and black-hole growth. It was great! Beta Lusso (MPIA) has a very nice argument about dust-obscured quasars: When she and her team fit the spectral energy distributions of non-obscured quasars, they find that more than half of the light from the central engine is being absorbed and re-radiated by an optically thick component (usually called, leadingly, "the torus"). If more than half of the photons are absorbed by an optically thick component, then the simplest, basic prediction is that (for randomly placed observers) more than half of the quasars should be strongly obscured. Great argument! Of course there are ways around it (optically thick material might be in a heterogeneous web of low covering factor; there might be strong temperature gradients in the optically thick material that lead to anisotropies in emission, etc), but it is a solid order-of-magnitude argument.
Before that, and partly starting the obscuration discussion, Nic Ross (LBL) showed some strange BOSS quasars, which were selected in the optical (by Bovy's XDQSO, I presume) but which turn out to be extremely bright in WISE 22-micron data. So bright, indeed, that naïve estimates make them among the most luminous objects in the Universe. (They might even be gravitationally magnified). The odd thing is that they have this huge infrared luminosity but show no sign in the optical of being reddened or obscured. The only clue is that (perhaps) they have large equivalent widths for their narrow lines. Nic: Did I get that right?
Yup!
ReplyDeleteNote however, they weren't just selected by XDQSO; a few are selected on their radio properties (FIRST sources) adding to the intrigue!