Studies of the cosmic microwave background (CMB) radiation have driven the current era of precision cosmology. The tightest cosmological constraints to date have been derived from the primary CMB anisotropies, which predominantly probe the universe in its infancy. However, CMB experiments have recently entered a new regime in which constraints derived from the secondary anisotropies -- sourced by effects between our vantage point and the surface of last scattering -- substantially improve upon those derived from the primary anisotropies alone. Moreover, the secondary anisotropies contain valuable astrophysical information about the distribution and thermodynamic properties of baryons and dark matter at late times. I will describe new approaches to extract information from these signals, highlighting recent results related to the thermal (tSZ) and kinematic Sunyaev-Zel'dovich (kSZ) effects, which refer to the Compton-scattering of CMB photons off ionized gas with high temperature or non-zero bulk momentum, respectively. In particular, I will show how the kSZ effect probes the abundance of ionized gas in and around modern-day galaxies, which I have used to resolve the long-standing "missing baryon problem". I will then discuss new methods for combining multi-frequency CMB data to extract these signals in the presence of large (and correlated) foregrounds, with additional applications to CMB polarization data. I will conclude with a look ahead to such measurements with the Simons Observatory (SO), focusing on methods to determine the optimal frequency coverage of the large-aperture SO telescope for secondary anisotropy science, including CMB lensing.
New Information in Ancient Photons: Novel Approaches to CMB Foregrounds and Secondary Anisotropies
Colin Hill (IAS)
Thursday, 25 January 2018