Radio galaxy populations and the multitracer technique: Pushing the limits on primordial non-gaussianity

Abstract

We explore the use of different radio galaxy populations as tracers of different mass haloes and therefore, with different bias properties, to constrain primordial non-Gaussianity of the local type.We perform a Fisher matrix analysis based on the predicted auto- and cross-angular power spectra of these populations, using simulated redshift distributions as a function of detection flux and the evolution of the bias for the different galaxy types (star-forming galaxies, starburst galaxies, radio-quiet quasars, FR I and FR II AGN galaxies). We show that such a multitracer analysis greatly improves the information on non-Gaussianity by drastically reducing the cosmic variance contribution to the overall error budget. By applying this method to future surveys, we predict a constraint of σfnl = 3.6 on the local non-Gaussian parameter for a galaxy detection flux limit of 10 μJy and σfnl = 2.2 for 1 μJy.We show that this significantly improves on the constraints obtained when using the whole undifferentiated populations (σfnl = 48 for 10 μJy and σfnl = 12 for 1 μJy). We conclude that continuum radio surveys alone have the potential to constrain primordial non-Gaussianity to an accuracy at least a factor of 2 better than the present constraints obtained with Planck data on the cosmic microwave background bispectrum, opening a window to obtain σfnl ~ 1 with the Square Kilometre Array. © 2014 The Authors.