Constraining magnetic fields in the circumgalactic medium

JX Prochaska�- Monthly Notices of the Royal Astronomical�…, 2020 - academic.oup.com
Monthly Notices of the Royal Astronomical Society, 2020academic.oup.com
We study the properties of magnetic fields in the circumgalactic medium (CGM) of z< 1
galaxies by correlating Faraday rotation measures (RMs) of∼ 1000 high-redshift radio
sources with the foreground galaxy number density estimated from the DESI Legacy
Imaging Surveys. This method enables us to extract signals of RMs contributed by
intervening gas around multiple galaxies. Our results show that there is no detectable
correlation between the distribution of RMs and the number of foreground galaxies, contrary�…
Abstract
We study the properties of magnetic fields in the circumgalactic medium (CGM) of z < 1 galaxies by correlating Faraday rotation measures (RMs) of ∼1000 high-redshift radio sources with the foreground galaxy number density estimated from the DESI Legacy Imaging Surveys. This method enables us to extract signals of RMs contributed by intervening gas around multiple galaxies. Our results show that there is no detectable correlation between the distribution of RMs and the number of foreground galaxies, contrary to several previous results. Utilizing the non-detection signals, we estimate 3σ upper limits to the RMs from the CGM of within�50�kpc and at separations of 100�kpc. By adopting a column density distribution of ionized gas obtained from absorption-line measurements, we further estimate the strengths of coherent magnetic fields parallel to the line of sight of in the CGM. We show that the estimated upper limits of RMs and magnetic field strengths are sufficient to constrain outputs of recent galaxy magnetohydrodynamic simulations. Finally, we discuss possible causes for the inconsistency between our results and previous works.
Oxford University Press