High-Velocity Clouds in the Nearby Spiral Galaxy M 83

Type Journal Article
Names Eric D. Miller, Joel N. Bregman, Bart P. Wakker
Publication The Astrophysical Journal
Volume 692
Issue 1
Pages 470-491
Date February 1, 2009
URL http://adsabs.harvard.edu/abs/2009ApJ...692..470M
Library Catalog NASA ADS
Abstract We present deep H I 21 cm and optical observations of the face-on spiral galaxy M 83 obtained as part of a project to search for high-velocity clouds (HVCs) in nearby galaxies. Anomalous-velocity neutral gas is detected toward M 83, with 5.6 × 107 M sun of H I contained in a disk rotating 40-50 km s-1 more slowly in projection than the bulk of the gas. We interpret this as a vertically extended thick disk of neutral material, containing 5.5% of the total H I within the central 8 kpc. Using an automated source detection algorithm to search for small-scale H I emission features, we find eight distinct, anomalous-velocity H I clouds with masses ranging from 7 × 105 to 1.5 × 107 M sun and velocities differing by up to 200 km s-1 compared to the H I disk. Large on-disk structures are coincident with the optical spiral arms, while unresolved off-disk clouds contain no diffuse optical emission down to a limit of 27 r' mag per square arcsec. The diversity of the thick H I disk and larger clouds suggests the influence of multiple formation mechanisms, with a galactic fountain responsible for the slowly rotating disk and on-disk discrete clouds, and tidal effects responsible for off-disk cloud production. The mass and kinetic energy of the H I clouds are consistent with the mass exchange rate predicted by the galactic fountain model. If the HVC population in M 83 is similar to that in our own Galaxy, then the Galactic HVCs must be distributed within a radius of less than 25 kpc.
Tags Galaxies: ISM, Radio Lines: Galaxies, galaxies: individual: M 83, galaxies: kinematics and dynamics
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