The low-frequency cosmic microwave background

Abstract

The Planck satellite’s highly precise measurements of the temperature and polarization properties of the cosmic microwave background (CMB) have provided detailed information about the cosmological model, but other features of the CMB remain largely inaccessible due to the low frequencies at which their signals appear. One such feature is its spectral distortion from a perfect blackbody, which is governed by Compton scattering of photons to increasing distances during recombination and, as such, contains imprints of primordial density structure. David Zegeye and colleagues propose the use of the Square Kilometer Array (SKA) to measure these spectral distortions, and demonstrate SKA’s future effectiveness as a probe of primordial non-Gaussianity.

The authors use a Fisher matrix approach to simulate the angular cross power spectra of a spectral distortion signal, as might be obtained with SKA’s medium-frequency array in single-dish mode, with temperature and polarization measurements from the upcoming CMB space mission LiteBIRD. Accounting for multiple Galactic and extragalactic foreground contaminants in the SKA wavelength window and adopting a careful calibration strategy, they show that the two instruments will provide highly complementary measurements, with their most realistic setup forecast to improve current constraints of the local primordial non-Gaussianity f_NL at this spatial scale by a factor of ~30.