The circumgalactic medium (CGM) is where gas accreting from cosmic filaments and recycled gas interplay, and it serves as a reservoir of fuel for galactic star formation. Its diffuse, multiphase nature and physical processes spanning from cosmological scales to pc-scale gas physics make the CGM challenging to study both observationally and theoretically. With advances in hydrodynamic simulations and UV spectroscopy with HST/COS, there has been significant progress in the past decade, and we now have a general picture of the CGM. However, most extragalactic CGM studies using absorption spectroscopy probe only one pencil-beam sight line per galaxy, so they are largely statistical, and the region close to the star-forming disk remains difficult to probe.
The Milky Way serves as a unique laboratory in this respect, with extensive data including hundreds of quasar sight lines and H I 21 cm emission surveys. These observations resolve multiphase clouds in the halo, allowing us to study them on small scales. I study these resolved gas structures to better understand the physical processes at small scales and in the inner halo.
