2006ApJ...646L..53C

We report that neutral hydrogen (H I) gas clouds, resembling high-velocity clouds (HVCs) observed in the Milky Way (MW), appear in MW-sized disk galaxies formed in high-resolution Lambda cold dark matter (ΛCDM) cosmological simulations that include gas dynamics, radiative cooling, star formation, supernova feedback, and metal enrichment. Two such disk galaxies are analyzed, and H I column density and velocity distributions in all-sky Aitoff projections are constructed. The simulations demonstrate that ΛCDM is able to create galaxies with sufficient numbers of anomalous velocity gas clouds consistent with the HVCs observed within the MW, and that they are found within a galactocentric radius of 150 kpc. We also find that one of the galaxies has a polar gas ring with radius 30 kpc that appears as a large structure of HVCs in the Aitoff projection. Such large structures may have an origin similar to that of extended HVCs observed in the MW, such as Complex C.