Constraints on Inflationary Gravitational Waves with Two Years of SPT-3G Data

TL;DR

This paper reports measurements of the B-mode polarization of the CMB using SPT-3G data, constraining inflationary gravitational waves with improved noise mitigation and foreground characterization, resulting in an upper limit on the tensor-to-scalar ratio.

Contribution

It introduces new techniques for atmospheric noise mitigation and provides the first constraints on inflationary gravitational waves from SPT-3G data.

Findings

Foreground power consistent with BICEP/Keck in the survey area

Achieved a white noise level of 9.3 μK-arcmin at ℓ~500

Placed a 95% upper limit of r < 0.25 on tensor-to-scalar ratio

Abstract

We present a measurement of the $B$-mode polarization power spectrum of the cosmic microwave background anisotropies at 32 $\le$ $\ell$ $<$ 502 for three bands centered at 95, 150, and 220 GHz using data from the SPT-3G receiver on the South Pole Telescope. This work uses SPT-3G observations from the 2019 and 2020 winter observing seasons of a $\sim$1500 deg$^2$ patch of sky that directly overlaps with fields observed with the BICEP/Keck family of telescopes, and covers part of the proposed Simons Observatory and CMB-S4 deep fields. Employing new techniques for mitigating polarized atmospheric noise, the SPT-3G data demonstrates a white noise level of 9.3 (6.7) $\mu$K-arcmin at $\ell \sim 500$ for the 95 GHz (150 GHz) data, with a $1/\ell$ noise knee at $\ell$=128 (182). We fit the observed six auto- and cross-frequency $B$-mode power spectra to a model including lensed $\Lambda$CDM $B$-modes and a combination of Galactic and extragalactic foregrounds. This work characterizes foregrounds in the vicinity of the BICEP/Keck survey area, finding foreground power consistent with that reported by the BICEP/Keck collaboration within the same region, and a factor of $\sim$ 3 higher power over the full SPT-3G survey area. Using SPT-3G data over the BICEP/Keck survey area, we place a 95% upper limit on the tensor-to-scalar ratio of $r < 0.25$ and find the statistical uncertainty on $r$ to be $\sigma(r) = 0.067$.