Prof. Matt Jarvis

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.

Abstract:

We present the results of a study which uses the 3CRR sample of radio-loud active galactic nuclei (AGN) to investigate the evolution of the hlack-hole: spheroid relation in the most massive early-type galaxies from 0 < z < 2. Radioloud unification is exploited to obtain virial (line-width) black-hole mass estimates from the 3CRR quasars, and stellar mass estimates from the 3CRR radio galaxies, thereby providing black-hole and stellar mass estimates for a single population of early-type galaxies. At low redshift (z < 1) the 3CRR sample is consistent with a black-hole:spheroid ratio of Mbh/Msph ≃ 0.002, in good agreement with that observed locally for quiescent galaxies of similar stellar mass (Msph ≃ 5 × 10 11M⊙). However, over the redshift interval 0 < z < 2 the 3CRR black-hole:spheroid ratio is found to evolve as M bh/Msph ∝ (1 + z)2-07±0.76, reaching Mbh/Msph ≃ 0.008 by redshift z ≃ 2. This evolution is found to be inconsistent with the local black-hole:spheroid ratio remaining constant at a moderately significant level (98%). If confirmed, the detection of evolution in the 3CRR black-hole:spheroid mass ratio further strengthens the evidence that, at least for massive early-type galaxies, the growth of the central supermassive black hole may be completed before that of the host spheroid. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.

Abstract:

Gamma-ray bursts (GRBs) and their afterglows are the most brilliant transient events in the Universe. Both the bursts themselves and their afterglows have been predicted to be visible out to redshifts of z ≈ 20, and therefore to be powerful probes of the early Universe1,2. The burst GRB 000131, at z = 4.50, was hitherto the most distant such event identified3. Here we report the discovery of the bright near-infrared afterglow of GRB 050904 (ref. 4). From our measurements of the near-infrared afterglow, and our failure to detect the optical afterglow, we determine the photometric redshift of the burst to be z = 6.39-0.12+0.11 (refs 5-7). Subsequently, it was measured8 spectroscopically to be z = 6.29 ± 0.01, in agreement with our photometric estimate. These results demonstrate that GRBs can be used to trace the star formation, metallicity, and reionization histories of the early Universe. © 2006 Nature Publishing Group.