Measurements of the E-Mode Polarization and Temperature-E-Mode Correlation of the CMB from SPT-3G 2018 Data

TL;DR

This work presents the first science results from the SPT-3G instrument, measuring the CMB $E$-mode polarization power spectrum ($EE$) and temperature-$E$-mode cross-spectrum ($TE$) over $300 \le \ell < 3000$ from a $\sim1500$ deg$^2$ sky patch in 2018. Using a multifrequency pseudo-$C_\ell$ approach with cross-spectra across six frequency combinations, the team obtains unbiased bandpowers, accounts for transfer functions, beams, and calibration, and validates the results with extensive simulations and null tests. The inferred cosmological parameters within the $\Lambda$CDM framework are consistent with Planck, with $H_0 = 68.8 \pm 1.5$ km s$^{-1}$ Mpc$^{-1}$, $\sigma_8 = 0.789 \pm 0.016$, and a lensing amplitude $A_L = 0.98 \pm 0.12$; combining SPT-3G with Planck reduces the parameter-space volume by about a factor of 1.5. The results demonstrate that polarization measurements from SPT-3G robustly support the standard cosmological model and offer a complementary, high-precision probe of mid-to-small angular scales, with significant gains expected as the 2018 data were partially limited by detector availability. The study also highlights the potential for future SPT-3G data to further tighten constraints and illuminate physics beyond the standard model.

Abstract

We present measurements of the $E$-mode ($EE$) polarization power spectrum and temperature-$E$-mode ($TE$) cross-power spectrum of the cosmic microwave background using data collected by SPT-3G, the latest instrument installed on the South Pole Telescope. This analysis uses observations of a 1500 deg$^2$ region at 95, 150, and 220 GHz taken over a four month period in 2018. We report binned values of the $EE$ and $TE$ power spectra over the angular multipole range $300 \le \ell < 3000$, using the multifrequency data to construct six semi-independent estimates of each power spectrum and their minimum-variance combination. These measurements improve upon the previous results of SPTpol across the multipole ranges $300 \le \ell \le 1400$ for $EE$ and $300 \le \ell \le 1700$ for $TE$, resulting in constraints on cosmological parameters comparable to those from other current leading ground-based experiments. We find that the SPT-3G dataset is well-fit by a $Λ$CDM cosmological model with parameter constraints consistent with those from Planck and SPTpol data. From SPT-3G data alone, we find $H_0 = 68.8 \pm 1.5 \mathrm{km\,s^{-1}\,Mpc^{-1}}$ and $σ_8 = 0.789 \pm 0.016$, with a gravitational lensing amplitude consistent with the $Λ$CDM prediction ($A_L = 0.98 \pm 0.12$). We combine the SPT-3G and the Planck datasets and obtain joint constraints on the $Λ$CDM model. The volume of the 68% confidence region in six-dimensional $Λ$CDM parameter space is reduced by a factor of 1.5 compared to Planck-only constraints, with only slight shifts in central values. We note that the results presented here are obtained from data collected during just half of a typical observing season with only part of the focal plane operable, and that the active detector count has since nearly doubled for observations made with SPT-3G after 2018.

Figures (14)

• Figure 1: The SPT-3G 1500 deg$^2$ survey field (orange, solid) overlaid on a Planck map of thermal dust emission planck15-10. Also shown are the the SPTpol 500 deg$^2$ field henning18(green, dashed) and the SPT-SZ 2500 deg$^2$ field story13(gray, dot-dashed).
• Figure 2: SPT-3G 2018 150 GHz temperature (top), Stokes $Q$(middle), and Stokes $U$(bottom) maps. Note the factor of ten difference in color scale between temperature and polarization maps. The data have been filtered to remove features larger than $\sim 0.5^\circ$, and the polarization maps have been smoothed by a $6'$ FWHM Gaussian.
• Figure 3: SPT-3G 2018 150 GHz $E$-mode polarization map. The data have been filtered to remove features larger than $\sim 0.5^\circ$, and the map has been smoothed by a $6'$ FWHM Gaussian.
• Figure 4: Temperature and polarization noise power spectra, corrected for the transfer functions of TOD processing. In each subplot, the left-hand vertical axis displays the noise in units of $\mu$K$^2$, while the right-hand vertical axis displays the equivalent map depth in units of $\mu$K-arcmin.
• Figure 5: Filter transfer functions for 150 GHz $T\!E$ and $E\!E$ power spectra, computed using 250 TOD simulations of the full SPT-3G 2018 dataset. The difference between the $T\!E$ and $EE$ transfer functions is caused by the common-mode filter.