The Astrophysical Journal (Jan 2024)

CLASS Angular Power Spectra and Map-component Analysis for 40 GHz Observations through 2022

  • Joseph R. Eimer,
  • Yunyang Li,
  • Michael K. Brewer,
  • Rui Shi,
  • Aamir Ali,
  • John W. Appel,
  • Charles L. Bennett,
  • Sarah Marie Bruno,
  • Ricardo Bustos,
  • David T. Chuss,
  • Joseph Cleary,
  • Sumit Dahal,
  • Rahul Datta,
  • Jullianna Denes Couto,
  • Kevin L. Denis,
  • Rolando Dünner,
  • Thomas Essinger-Hileman,
  • Pedro Fluxá,
  • Johannes Hubmayer,
  • Kathleen Harrington,
  • Jeffrey Iuliano,
  • John Karakla,
  • Tobias A. Marriage,
  • Carolina Núñez,
  • Lucas Parker,
  • Matthew A. Petroff,
  • Rodrigo A. Reeves,
  • Karwan Rostem,
  • Deniz A. N. Valle,
  • Duncan J. Watts,
  • Janet L. Weiland,
  • Edward J. Wollack,
  • Zhilei Xu,
  • Lingzhen Zeng

DOI
https://doi.org/10.3847/1538-4357/ad1abf
Journal volume & issue
Vol. 963, no. 2
p. 92

Abstract

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Measurement of the largest angular scale ( ℓ < 30) features of the cosmic microwave background (CMB) polarization is a powerful way to constrain the optical depth to reionization and search for the signature of inflation through the detection of primordial B -modes. We present an analysis of maps covering 73.6% of the sky made from the 40 GHz channel of the Cosmology Large Angular Scale Surveyor (CLASS) from 2016 August to 2022 May. Taking advantage of the measurement stability enabled by front-end polarization modulation and excellent conditions from the Atacama Desert, we show this channel achieves higher sensitivity than the analogous frequencies from satellite measurements in the range 10 < ℓ < 100. Simulations show the CLASS linear (circular) polarization maps have a white noise level of $125(130)\,\mu {\rm{K}}\,\mathrm{arcmin}$ . We measure the Galaxy-masked EE and BB spectra of diffuse synchrotron radiation and compare to space-based measurements at similar frequencies. In combination with external data, we expand measurements of the spatial variations of the synchrotron spectral energy density (SED) to include new sky regions and measure the diffuse SED in the harmonic domain. We place a new upper limit on a background of circular polarization in the range 5 < ℓ < 125 with the first bin showing D _ℓ < 0.023 $\mu {{\rm{K}}}_{\mathrm{CMB}}^{2}$ at 95% confidence. These results establish a new standard for recovery of the largest-scale CMB polarization from the ground and signal exciting possibilities when the higher sensitivity and higher-frequency CLASS channels are included in the analysis.

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