Hidden Galactic Accretion: The Discovery of Low-Velocity Halo Clouds

Details Hidden Galactic Accretion: The Discovery of Low-Velocity Halo Clouds Hidden Galactic Accretion: The Discovery of Low-Velocity Halo Clouds

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.1408p&link_type=abstract

American Astronomical Society, AAS Meeting #211, #14.08; Bulletin of the American Astronomical Society, Vol. 39, p.760

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High-Velocity Clouds (HVCs) have been thought to be part of the Galactic accretion process since their discovery more than 40 years ago. Two modes through which HVCs may be generated and contribute to the ongoing growth of our Galaxy are (1) the tidal stripping of satellite galaxies and (2) the fragmented condensation of the Galaxy's hot baryonic halo. We have run cosmological Tree-SPH simulations of a Milky-Way sized galaxy, in which we can resolve clouds down to 10^5 M&sun;, in an attempt to probe the cooling halo accretion process. The simulations show that this HVC generation mechanism can indeed reproduce the characteristics of observed population of HVCs, including the flux, velocity and cloud clustering properties. These simulations also predict an equally large population of halo clouds moving at lower radial velocities: Low-Velocity Halo Clouds (LVHCs). These clouds would not be observed as HVCs, but would rather be confused with local disk gas. Taking advantage of the known empirical result that HVCs have undetectably low infrared dust flux compared to their 21cm column, we search for these clouds in the preliminary GALFA-HI survey and IRAS. We announce the discovery of the first examples of these clouds, and describe their properties. This work was supported in part by NSF grant AST 04-06987 and NSF grant AST 07-09347.

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