MeerKAT

Abstract:

We present polarization data for 32 mainly southern pulsars at 8.4 GHz. The observations show that the polarization fraction is low in most pulsars at this frequency except for the young, energetic pulsars which continue to show polarization fractions in excess of 60 per cent. All the pulsars in the sample show evidence for conal emission with only one third also showing core emission. Many profiles are asymmetric, with either the leading or the trailing part of cone not detectable. Somewhat surprisingly, the asymmetric profiles tend to be more polarized than the symmetrical profiles. Little or no pulse narrowing is seen between 1 and 8.4 GHz. The spectral behaviour of the orthogonal polarization modes and radius to frequency mapping can likely account for much of the observational phenomenology. Highly polarized components may orginate from higher in the magnetosphere than unpolarized components.

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.