Princeton University Gravity Group Lunch Seminar

Abstract 1: The Simons Observatory Small Aperture Telescopes (SATs) employ a continuously rotating broadband half-wave plate (HWP) to access the primordial gravitational wave generated B-mode polarization signal at degree scales. I will provide a brief overview of how we observe with a HWP and how it changes the time-ordered data (TOD). I will discuss some of the systematics induced by a HWP, and our estimation of those systematics levels for the SO. Lastly, I will discuss my work on the modified time-ordered data processing pipeline in the presence of a HWP and the methods we plan to employ for data quality checks and systematics mitigation using intermediate data products from the TOD processing. I will demonstrate this data processing on simulated data and data from the first 90/150 GHz SAT in-lab integration and commissioning tests.

Abstract 2: Detecting the imprint of primordial gravitational waves on the B-mode polarization of the Cosmic Microwave Background (CMB) is currently one of the most compelling fundamental science cases for cosmology. Arguably the largest source of systematic uncertainty for both space and ground experiments will be contamination by the astrophysical foreground signal from the Milky Way. The separation of CMB radiation and foregrounds can be performed either in real space or in Fourier space. The effects of the different approaches will become crucial at the sensitivity of the forthcoming CMB experiments (e.g. CMB-S4, LiteBIRD). In this talk I will compare different foreground cleaning methods, including a two-step self-consistent "hybrid" method. This method combines some of the advantages of both approaches, by cleaning out the spatially constant part of the foregrounds at the map level, assuming nothing about the scale dependence of foregrounds, and modelling the residual frequency maps at power-spectrum level. We validate the method using Simons-Observatory-like simulated observations, recovering an unbiased estimate of the tensor-to-scalar ratio r for a wide range of realistic foreground scenarios.