A young, dusty, compact radio source within a Lyα halo
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 389:2 (2008) 792-798
The extreme, red afterglow of GRB 060923A: distance or dust?
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 388:4 (2008) 1743-1750
Mid-Infrared SED-Based Selection of Type-2 Quasars.
American Astronomical Society Meeting Abstracts 39 (2007) 797-797
Low accretion rates at the AGN cosmic downsizing epoch
ArXiv 0709.0786 (2007)
Abstract:
Context: X-ray surveys of Active Galactic Nuclei (AGN) indicate `cosmic downsizing', with the comoving number density of high-luminosity objects peaking at higher redshifts (z about 2) than low-luminosity AGN (z<1). Aims: We test whether downsizing is caused by activity shifting towards low-mass black holes accreting at near-Eddington rates, or by a change in the average rate of accretion onto supermassive black holes. We estimate the black hole masses and Eddington ratios of an X-ray selected sample of AGN in the Chandra Deep Field South at z<1, probing the epoch where AGN cosmic downsizing has been reported. Methods: Black hole masses are estimated both from host galaxy stellar masses, which are estimated from fitting to published optical and near-infrared photometry, and from near-infrared luminosities, applying established correlations between black hole mass and host galaxy properties. Both methods give consistent results. Comparison and calibration of possible redshift-dependent effects is also made using published faint host galaxy velocity dispersion measurements. Results: The Eddington ratios in our sample span the range 10^{-5} to 1, with median log(L_bol/L_Edd)=-2.87, and with typical black hole masses about 10^{8} solar masses. The broad distribution of Eddington ratios is consistent with that expected for AGN samples at low and moderate luminosity. We find no evidence that the CDF-S AGN population is dominated by low-mass black holes accreting at near-Eddington ratios and the results suggest that diminishing accretion rates onto average-sized black holes are responsible for the reported AGN downsizing at redshifts below unity.The discovery of a massive supercluster at z = 0.9 in the UKIDSS deep eXtragalactic survey
Monthly Notices of the Royal Astronomical Society 379:4 (2007) 1343-1351