Constraining the average magnetic field in galaxy clusters with current and upcoming CMB surveys

TL;DR

This paper uses Planck data to set lower limits on galaxy cluster magnetic fields via the non-thermal Sunyaev-Zeldovich effect and discusses how future CMB surveys could tighten these constraints.

Contribution

It provides the first upper limits on the non-thermal SZ signal in radio-halo clusters and forecasts improved magnetic field constraints with upcoming surveys.

Findings

No direct detection of the ntSZ signal in Planck data.

Lower limits on magnetic fields range from 0.01 to 0.24 microGauss.

Future surveys could improve constraints by a factor of two.

Abstract

Galaxy clusters that host radio halos indicate the presence of population(s) of non-thermal electrons. These electrons can scatter low-energy photons of the Cosmic Microwave Background, resulting in the non-thermal Sunyaev-Zeldovich (ntSZ) effect. We measure the average ntSZ signal from 62 radio-halo hosting clusters using the $Planck$ multi-frequency all-sky maps. We find no direct evidence of the ntSZ signal in the $Planck$ data. Combining the upper limits on the non-thermal electron density with the average measured synchrotron power collected from the literature, we place lower limits on the average magnetic field strength in our sample. The lower limit on the volume-averaged magnetic field is $0.01-0.24\,\mu$G, depending on the assumed power-law distribution of electron energies. We further explore the potential improvement of these constraints from the upcoming Simons Observatory and Fred Young Submillimeter Telescope (FYST) of the CCAT-prime collaboration. We find that combining these two experiments, the constraints will improve by a factor of two, which can be sufficient to rule out some power-law models.