Program: GS-2008B-Q-86

Title:The evolution of luminous obscured quasars: Bright 24 micron sources
PI:Susan Ridgway
Co-I(s): Mark Lacy, Anna Sajina, Craig Harrison, Lisa Storrie-Lombardi, Duncan Farrah

Abstract

We are currently undertaking a spectroscopic survey of luminous AGN and quasars selected in the mid-infrared from Spitzer shallow surveys. Mid-infrared selection is much less biased with respect to obscuration than optical and X-ray techniques, and hence enables the discovery of obscured quasars as well as normal, unobscured ones. Our survey therefore provides an unique opportunity to construct luminosity functions for both obscured and unobscured quasars selected in the same way and covering similar redshifts and luminosities. Our 4m class spectroscopic observations have so far have yielded about 150 redshifts, but our luminosity functions are lacking lower luminosity objects at high redshift and high luminosity objects at low redshift. We have been granted 3 nights of classical time at Gemini S to find lower luminosity z > 1 obscured quasars by targeting objects with faint 24 micron fluxes. We have been granted two nights at SOAR with the Goodman Spectrograph, which should allow us to target about half the available bright 24 micron objects. We are therefore requesting poor weather Gemini S GMOS time to obtain redshifts for another 15 bright 24 micron objects. Obtaining sufficient numbers of these thinly spread, brighter 24 micron sources is vital to filling out this missing portion of the luminosity/redshift plane, and will allow us to disentangle any luminosity dependence of the obscured quasar fraction from its evolution with redshift. This will allow us to test models of the obscured quasar population, in particular at the highest redshifts and luminosities where we are seeing a previously undiscovered population of obscured objects.

Publications using this program's data