Florian Rünger
University of Potsdam
Abstract
The accretion and processing of neutral and ionized gas is a substantial ingredient in the evolution of the Milky Way. From the position of the Sun, circumgalactic gas flows in the Milky Way halo are known to span a large range in radial velocities, but the complex kinematics of the circumgalactic medium (CGM) cannot be fully reconstructed from observations. This is because of the blending with foreground interstellar gas in the Milky Way disk. In this paper, we use the three high-res MHD simulation from the Hestia project to systematically investigate the radial-velocity distribution of neutral-hydrogen (H I) clouds in the CGM in the (simulated) Local Standard of Rest (LSR) velocity frame. There is the general trend that the majority of the extra-planar H I at z > 2 kpc above the plane is confined to a velocity range |vLSR | ≤ 100 km s−1, implying that the gas is (at least partly) co-rotating with the underlying disk. The two most realistic Milky Way realizations, the CGM velocity distribution are skewed towards negative velocities, indicating a net-accretion of neutral gas. These results are in line with the statistics from UV absorption-lines measurements of the Milky Way CGM. Our study also supports a scenario in which a substantial fraction of the Milky Way’s CGM is hiding at |vLSR | ≤ 100 km s−1 where it spectral signatures are covered by nearby nterstellar gas features.
Scientific theme
Circumgalactic medium, High-velocity halo cloud, Milky Way