Radio spectral properties of faint source populations

Abstract

In this thesis, the radio spectral properties of the faint sources in two deep ex- tragalactic radio survey areas are investigated to aid in the discrimination between AGN and starbursts. The detailed 4-point radio spectra of two X-ray bright, optically quiescent sources in the 13^ XMM/Newton/ Chandra survey area are measured, and found to be flat in one case, and steep (a ~ -0.6) in another. Deep imaging of both the 13^ and 1H XMM/Newton/ Chandra survey fields at 610 MHz with the GMRT are presented. To detection limits of ~320 and 300/^Jy beam"1, 206 and 223 sources are discovered in the 13H and 1H fields respectively. A deep 1.4 GHz survey of the 1H field is performed with the VLA. To a detection limit of 45 /xJy, 432 sources are discovered. The source counts at both 610 MHz and 1.4 GHz agree with those in other deep fields, and can both be fit with similar models consisting of standard AGN source count models combined with a population of steep spectrum (a = -0.7) star burst galaxies undergoing power law evolution with an index of 2.5 and 2.6 at 1.4 GHz and 610 MHz respectively. The catalogues of these three surveys are combined with the results of an earlier deep 1.4 GHz survey of the 13^ field to calculate useful radio spectral indices for 192 faint radio sources. Assuming that starburst galaxies exhibit spectra within -1 < a < -0.4; 83 sources can be identified as AGN on radio spectral grounds.

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