Cosmology

Abstract:

We investigate the link between ionised Fe X-ray line emission and continuum emission in the bright nearby AGN, Mrk 766. A new long (433 ks) XMM-Newton observation is analysed, together with archival data from 2000 and 2001. The contribution from ionised line emission is measured and its time variations on short (5-20 ks) timescales are correlated with the continuum emission. The ionised line flux is found to be highly variable and to be strongly correlated with the continuum flux, demonstrating an origin for the ionised line emission that is co-located with the continuum emission. Most likely the emission is ionised reflection from the accretion disc within a few A.U. of the central black hole, and its detection marks the first time that such an origin has been identified other than by fitting to spectral line profiles. Future observations may be able to measure a time lag and hence achieve reverberation mapping of AGN at X-ray energies.

Abstract:

In this review we highlight what has been gained from a host of surveys covering a large proportion of the electromagnetic spectrum with respect to active galactic nuclei with emphasis placed on the powerful high-redshift radio galaxies and radio-loud quasars. We focus on recent results which consider the cosmic evolution of radio galaxies and radio-loud quasars, their host galaxies and black-hole masses. We then briefly highlight the potential of combining surveys at other wavelengths, such as the SDSS and Spitzer surveys, for investigating these topics. Finally, we look forward to the new parameter space which will be opened up with the radio telescopes of the future, namely the LOFAR and the SKA. These new telescopes are likely to lead to a shift in radio survey science. The survey depths that are within the reach of these telescopes will mean that the dominant populations will no longer be AGN, but starburst and 'normal' galaxy populations out to z ≳ 2. However, the SKA will also have the ability to find and measure redshifts for every moderately powerful radio AGN in the Universe, providing a new and unique view of galaxy formation and evolution. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.

Abstract:

We present an alternative method to X-ray surveys for hunting down the high-redshift type-2 quasar population, using Spitzer and VLA data on the Spitzer First Look Survey. By demanding objects to be bright at 24 μm but faint at 3.6 μm, and combining this with a radio criterion, we find 21 type-2 radio-quiet quasar candidates at the epoch at which the quasar activity peaked. Optical spectroscopy with the WHT confirmed 10 of these objects to be type-2s with 1.4 ≤ z ≤ 4.2 while the rest are blank. There is no evidence for contamination in our sample, and we postulate that our 11 blank-spectrum candidates are obscured by kpc-scale dust as opposed to dust from a torus around the accretion disk. By carefully modelling our selection criteria, we conclude that, at high redshift, 50-80 % of the supermassive black hole growth is obscured by dust. ©2006 WILEY-VCH Verlag GmbH & Co. KGaA.