BEYONDPLANCK

XV. Limits on large-scale polarized anomalous microwave emission from Planck LFI and WMAP

¹ Institute of Theoretical Astrophysics, University of Oslo, Blindern, Oslo, Norway
e-mail: d.c.herman@astro.uio.no
² Department of Astrophysical Sciences, Princeton University, Princeton, NJ, 08544 USA
³ Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, Milano, Italy
⁴ INAF/IASF Milano, Via E. Bassini 15, Milano, Italy
⁵ INAF – Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, Trieste, Italy
⁶ Planetek Hellas, Leoforos Kifisias 44, Marousi, 151 25 Greece
⁷ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California, USA
⁸ Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2, Helsinki, Finland
⁹ Helsinki Institute of Physics, University of Helsinki, Gustaf Hällströmin katu 2, Helsinki, Finland
¹⁰ Computational Cosmology Center, Lawrence Berkeley National Laboratory, Berkeley, California, USA
¹¹ INFN, Sezione di Milano, Via Celoria 16, Milano, Italy
¹² Haverford College Astronomy Department, 370 Lancaster Avenue, Haverford, PA, USA
¹³ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
¹⁴ Dipartimento di Fisica, Università degli Studi di Trieste, Via A. Valerio 2, Trieste, Italy

Received: 10 January 2022
Accepted: 31 March 2022

Abstract

We constrained the level of polarized anomalous microwave emission (AME) on large angular scales using Planck Low-Frequency Instrument (LFI) and WMAP polarization data within a Bayesian cosmic microwave background (CMB) analysis framework. We modeled synchrotron emission with a power-law spectral energy distribution, as well as the sum of AME and thermal dust emission through linear regression with the Planck High-Frequency Instrument (HFI) 353 GHz data. This template-based dust emission model allowed us to constrain the level of polarized AME while making minimal assumptions on its frequency dependence. We neglected CMB fluctuations, but show through simulations that these fluctuations have a minor impact on the results. We find that the resulting AME polarization fraction confidence limit is sensitive to the polarized synchrotron spectral index prior. In addition, for prior means β_s < −3.1 we find an upper limit of p_AME^max ≲ 0.6% (95% confidence). In contrast, for means β_s = −3.0, we find a nominal detection of p_AME = 2.5 ± 1.0% (95% confidence). These data are thus not strong enough to simultaneously and robustly constrain both polarized synchrotron emission and AME, and our main result is therefore a constraint on the AME polarization fraction explicitly as a function of β_s. Combining the current Planck and WMAP observations with measurements from high-sensitivity low-frequency experiments such as C-BASS and QUIJOTE will be critical to improve these limits further.