Cosmological Constraints from a Measurement of the Polarization Power Spectra of the Cosmic Microwave Background with the SPTpol Experiment

Jason W. Henning, University of Colorado at Boulder


SPTpol is a polarization-sensitive receiver installed on the South Pole Telescope in its third season of mapping Cosmic Microwave Background (CMB) temperature and polarization anisotropies. The receiver contains 588 (180) dual polarization pixels at 150 (95) GHz comprising a total of 1536 transition edge sensor bolometers. In its first year, SPTpol mapped 100 deg2 to a depth of ~8 and 10 μK-arcmin at 150 GHz in temperature and polarization, respectively. With this deep field map, the SPTpol collaboration produced the first statistically significant detection (7.7 σ) of gravitational lensing B-mode polarization. Additionally, the SPTpol experiment just completed its first of three years mapping 500 deg2 to a depth of ~12 and 15 μK-arcmin in temperature and polarization at 150 GHz. High signal-to-noise measurements of the polarization power spectra from the survey will further constrain cosmological parameters and extensions to the ΛCDM cosmological model. Measurements of large-scale polarization anisotropies will also place tighter constraints on the existence of primordial B-mode polarization generated by gravitational waves from the epoch of inflation.

In this work we discuss the development of the SPTpol receiver and, in particular, the seven 150 GHz detector modules at the heart of the focal plane. We describe the observational strategies used during the first two seasons of SPTpol measurements as well as the reduction of detector timestreams into maps and CMB polarization power spectra. To extract constraints on cosmological parameters from the SPTpol power spectra we have written a new Bayesian likelihood module for the CosmoMC Markov Chain Monte Carlo package, which we also describe. Finally, we present cosmological constraints from the first year of SPTpol observations. Pre-existing constraints on ΛCDM parameters improve by a few percent with the inclusion of these data. While this is a modest step forward in our understanding of the early universe, the completed SPTpol dataset will have the power to tightly constrain the sum of neutrino masses and help determine the source of recently detected large-scale B-mode polarization.