Gravitational lensing of the cosmic microwave background: techniques and applications.

Abstract

We have entered an era of precision cosmology, in which the parameters of the standard cosmological model have been well constrained by observations. The cosmic microwave background (CMB) has played a vital role in providing these constraints, because the primordial CMB is sensitive to many of the cosmological parameters. The observed CMB is modified by secondary effects caused by photon interactions after the surface of last scattering. One such effect is gravitational lensing, the deflection of photons due to the matter that they pass. Gravitational lensing can be used to probe the total matter distribution, which is dominated by dark matter. CMB lensing also provides complementary cosmological information to that obtained from the CMB power spectrum, and can be used to break parameter degeneracies and improve constraints on dark energy and neutrino masses. We explore methods of reconstructing the lensing field from lensed CMB temperature and polarisation maps in real space, as an alternative to the harmonic space estimators currently in use, by extending an existing temperature real space estimator to CMB polarisation. Real space estimators have the advantage of being local in nature and they are thus equipped to deal with the nonuniform sky coverage, galactic cuts and point source excisions found in experimental data. We characterise some of the properties and limitations of these estimators and test them on simulated maps, finding that the reconstructions are accurate for large-scale lensing fields, and that the polarisation reconstructions improve on those from CMB temperature maps. Neutral hydrogen (HI) intensity mapping is expected to be a powerful probe of large scale structure and cosmology, and a number of current and planned experiments will be performing large intensity mapping surveys. HI is a biased tracer of the dark matter distribution, therefore HI observations will be correlated with CMB lensing reconstructions. We investigate the potential for measuring this cross-correlation using CMB lensing reconstructed from Advanced ACTPol observations and HI intensity mapping data from the Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX).We find that the CMB lensing-HI cross-correlation will be detectable with a total signal to noise ratio of between 20 and 50 in each of four bins in the HIRAX frequency range, which will allow us to constrain the HI bias on various scales over a wide redshift range (z = 0.8 to 2.5).