Evolution of Bias in the Radio Source Population

Sam Lindsay (University of Hertfordshire)

Evolution of Bias in the Radio Source Population


Much of cosmology is concerned with measures of large-scale structure of the Universe. Given the relative abundance of dark matter compared with observable light-emitting matter, the relationship between the two is crucial, and the galaxy mass bias parameter quantifies how strongly a galaxy population traces the underlying dark matter structure. In observing at radio wavelengths, we target the synchrotron emission of massive star-forming galaxies and AGN with a stronger bias than a similar optically-selected survey. The wide redshift range probed by deep radio surveys further enables study into the evolution of clustering properties over cosmic time. We match radio sources from the VLA FIRST survey (¿1 mJy @1.4 GHz) to optical sources over three 70 sq. deg. equatorial fields with spectroscopic redshifts from GAMA (r ¡ 19.8) and photometric redshifts from SDSS/UKIDSS (r ¡ 22). This provides an optically identified radio sample at z 0.5 of 4,000 galaxies, but we further use the publicly available SKADS semi-empirical simulation of extragalactic radio continuum sources to infer the redshift distribution of the 9,000 unmatched radio sources. Quantifying
the clustering of the radio populations through the two-point angular correlation function,
we may use Limber inversion and the redshift distribution to infer the spatial (rather than angular)
clustering properties. This allows us to calculate the mass bias from z 0.3 for the z¡0.5 matched
sources to z 1.55 for the unmatched sources, finding an increase with redshift indicative of more
massive high-redshift radio population.

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