Quantifying angular clustering in wide-area radio surveys

We quantify the angular clustering of radio galaxies in the NVSS and FIRST radio surveys using the two-point correlation function and the moments of counts-in-cells - both important points of comparison with theory. These investigations consistently demonstrate that the slope of the correlation function for radio galaxies agrees with that for optically-selected galaxies, gamma = 1.8. We describe how to disentangle the imprint of galaxy clustering from the two observational problems: resolution of radio galaxies into multiple components and gradients in source surface density induced by difficulties in processing "snapshot" radio observations (significant in both surveys below 15 mJy). This study disagrees in some respects with previous analyses of the angular clustering of radio galaxies.Comment: 26 pages, 13 figures, accepted for publication in MNRA

Evolution of AGN Space Densities and the FR Dichotomy

We focus on a comparison of the space densities of FRI and FRII extended radio sources at different epochs, and find that FRI and FRII sources show similar space density enhancements in various redshift ranges, possibly implying a common evolution.Comment: IAU Symposium 267 Proceeding - 1 pag

Searching for Large Scale Structure in Deep Radio Surveys

(Abridged Abstract) We calculate the expected amplitude of the dipole and higher spherical harmonics in the angular distribution of radio galaxies. The median redshift of radio sources in existing catalogues is z=1, which allows us to study large scale structure on scales between those accessible to present optical and infrared surveys, and that of the Cosmic Microwave Background (CMB). The dipole is due to 2 effects which turn out to be of comparable magnitude: (i) our motion with respect to the CMB, and (ii) large scale structure, parameterised here by a family of Cold Dark Matter power-spectra. We make specific predictions for the Green Bank (87GB) and Parkes-MIT-NRAO (PMN) catalogues. For these relatively sparse catalogues both the motion and large scale structure dipole effects are expected to be smaller than the Poisson shot-noise. However, we detect dipole and higher harmonics in the combined 87GB-PMN catalogue which are far larger than expected. We attribute this to a 2 % flux mismatch between the two catalogues. We also investigate the existence and extent of the Supergalactic Plane in the above catalogues. In a strip of +- 10 deg of the standard Supergalactic equator, we find a 3-sigma detection in PMN, but only 1-sigma in 87GB.Comment: 15 pages, 5 ps figures, Latex, Submitted to MNRA

A deep sky survey at 2700 MHZ

Virtually all conclusions on the physics of extragalactic radio sources have been derived from studies of those catalogued in sky surveys at or below the frequency of 408 MUz. Profound cosmological conclusions have also been drawn from studies of the source populations obtained in low frequency surveys«, This thesis presents the results of extragalactic source surveys at the comparatively high frequency of 2700 MHz, carried out over about 0.8 sr. with the 210 - foot telescope of the ANRAO at Parkes, N.S.W. The surveys are the first parts of the Parkes 2700 MHz survey which will extend eventually over the entire sky between declination -90° and declination +27°, the northernmost limit of observation for the Parkes telescope

Measurement of the angular correlation function of radio galaxies from the NRAO VLA Sky Survey

We quantify the angular distribution of radio sources in the NVSS by measuring the two-point angular correlation function. By careful consideration of the resolution of radio galaxies into multiple components, we are able to determine both the galaxy angular clustering and the size distribution of giant radio galaxies. The slope of the correlation function for radio galaxies agrees with that for other classes of galaxy, gamma = 1.8, with a 3D correlation length r_0 = 6 h^-1 Mpc (under certain assumptions). Calibration problems in the survey prevent clustering analysis below 10 mJy. About 7 per cent of radio galaxies are resolved by NVSS into multiple components, with a power-law size distribution. Our work calls into question previous analyses and interpretations of the angular correlation function from radio surveys.Comment: Accepted for publication as an MNRAS letter, 5 page

Astronomy below the survey threshold in the SKA era

Astronomy at or below the 'survey threshold' has expanded significantly since the publication of the original 'Science with the Square Kilometer Array' in 1999 and its update in 2004. The techniques in this regime may be broadly (but far from exclusively) defined as 'confusion' or 'P(D)' analyses (analyses of one-point statistics), and 'stacking', accounting for the flux-density distribution of noise-limited images co-added at the positions of objects detected/isolated in a different waveband. Here we discuss the relevant issues, present some examples of recent analyses, and consider some of the consequences for the design and use of surveys with the SKA and its pathfinders