Probing the Magneto-Ionized Circumgalactic Medium of M31 with HI and Rotation Measures

          @misc{ pirsa_PIRSA:25070030,
            doi = {10.48660/25070030},
            url = {https://pirsa.org/25070030},
            author = {Pisano, D.J.},
            keywords = {Cosmology},
            language = {en},
            title = {Probing the Magneto-Ionized Circumgalactic Medium of M31 with HI and Rotation Measures},
            publisher = {Perimeter Institute},
            year = {2025},
            month = {jul},
            note = {PIRSA:25070030 see, \url{https://pirsa.org}}
          }
          

Abstract

The circumgalactic medium (CGM) represents both a significant reservoir of baryons around galaxies as well as the region through which gas flows on to and out of galactic disks providing fuel for continued star formation. It is, however, challenging to study due to the low densities of gas in the CGM. Previous UV absorption studies have shown that the CGM is ubiquitous around star-forming galaxies. Project AMIGA has shown that the Andromeda Galaxy (M31), specifically, has an extensive CGM, which has further been confirmed by recent results from Fast Radio Bursts. Here, we present two complementary approaches to further characterize the CGM of M31. First, using archival rotation measure (RM) measurements of background radio point sources projected within the virial radius of M31, we present evidence of the existence of a magneto-ionized plasma extending out to $\gtrsim$100 kpc from M31. Second, using HI observations from the Green Bank Telescope (GBT) and MeerKAT, we show evidence of infalling gas being disrupted by the hot CGM at similar distances. Both observations confirm the presence of an extended, hot, ionized, and magnetized CGM around M31.