The Atacama Cosmology Telescope: CMB Polarization at $200<\ell<9000$

TL;DR

This paper presents detailed measurements of the CMB polarization from the Atacama Cosmology Telescope, confirming cosmological models and providing new insights into polarized point sources and calibration sources like the Crab Nebula.

Contribution

First detailed polarization measurements from ACTPol covering multiple sky regions, with results consistent with cosmological models and new polarization data for calibration sources.

Findings

E-mode polarization spectrum matches cosmological model predictions.

Polarized point source contamination is minimal at high multipoles.

Crab Nebula's polarization measured at 8.7% with a specific angle.

Abstract

We report on measurements of the cosmic microwave background (CMB) and celestial polarization at 146 GHz made with the Atacama Cosmology Telescope Polarimeter (ACTPol) in its first three months of observing. Four regions of sky covering a total of 270 square degrees were mapped with an angular resolution of $1.3'$. The map noise levels in the four regions are between 11 and 17 $\mu$K-arcmin. We present TT, TE, EE, TB, EB, and BB power spectra from three of these regions. The observed E-mode polarization power spectrum, displaying six acoustic peaks in the range $200<\ell<3000$, is an excellent fit to the prediction of the best-fit cosmological models from WMAP9+ACT and Planck data. The polarization power spectrum, which mainly reflects primordial plasma velocity perturbations, provides an independent determination of cosmological parameters consistent with those based on the temperature power spectrum, which results mostly from primordial density perturbations. We find that without masking any point sources in the EE data at $\ell<9000$, the Poisson tail of the EE power spectrum due to polarized point sources has an amplitude less than $2.4$ $\mu$K$^2$ at $\ell = 3000$ at 95\% confidence. Finally, we report that the Crab Nebula, an important polarization calibration source at microwave frequencies, has 8.7\% polarization with an angle of $150.7^\circ \pm 0.6^\circ$ when smoothed with a $5'$ Gaussian beam.