TIng-Wen Lan (UCSC)
Gas around galaxies, the circumgalactic medium (CGM), plays an essential role in our understanding of galaxy evolution. It is the interface between galaxies and the intergalactic medium where gas accretion and outflows --key drivers of galaxy evolution-- leave their signatures. To better understand the origin and fate of the CGM, it is crucial to probe magnetic fields around galaxies, a key component that controls the structure and survival of the CGM as suggested by recent magnetohydrodynamic simulations. In this talk, I will show that one can extract the properties of magnetic fields in the CGM 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. By doing so, we are able to obtain strict upper limits of RMs and corresponding magnetic field strengths around galaxies. Finally, I will show that our upper limits are sufficient to constrain outputs of recent galaxy magnetohydrodynamic simulations.