Relativistic corrections and non-Gaussianity in radio continuum surveys

Abstract

Forthcoming radio continuum surveys will cover large volumes of the observable Universe and will reach to high redshifts, making them potentially powerful probes of darkenergy, modified gravity and non-Gaussianity. Weconsider the continuum surveys with LOFAR, WSRT and ASKAP, and examples of continuum surveys withthe SKA. We extend recent work on these surveys by including redshift space distortions and lensing convergence in the radio source auto-correlation.In addition we compute the general relativistic (GR) corrections tothe angular power spectrum. These GR corrections to the standardNewtonian analysis of the power spectrum become significant onscales near and beyond the Hubble scale at each redshift. We find that the GR corrections are at most percent-level in LOFAR, WODAN and EMU surveys, but they can produceO(10%) changes for high enough sensitivity SKA continuum surveys. The signal is however dominated by cosmic variance, and multiple-tracer techniques will be needed to overcome this problem. The GR corrections are suppressed in continuum surveys because of theintegration over redshift — we expect that GR corrections will be enhanced for future SKA HI surveys in which the source redshifts will be known.We also provide predictions for the angular power spectra in the case where the primordialperturbations have local non-Gaussianity. We find that non-Gaussianity dominates over GR corrections, and rises above cosmic variance when fNL≳5 for SKA continuum surveys.