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Ongoing accretion onto galactic disks has been recently theorized to progressvia the unstable cooling of the baryonic halo into condensed clouds. Theseclouds have been identified as analogous to the High-Velocity Clouds (HVCs)observed in HI in our Galaxy. Here we compare the distribution of HVCs observedaround our own Galaxy and extra-planar gas around the Andromeda galaxy to thesepossible HVC analogs in a simulation of galaxy formation that naturallygenerates these condensed clouds. We find a very good correspondence betweenthese observations and the simulation, in terms of number, angular size,velocity distribution, overall flux and flux distribution of the clouds. Weshow that condensed cloud accretion only accounts for ~ 0.2 M_solar / year ofthe current overall Galactic accretion in the simulations. We also find thatthe simulated halo clouds accelerate and become more massive as they falltoward the disk. The parameter space of the simulated clouds is consistent withall of the observed HVC complexes that have distance constraints, except theMagellanic Stream which is known to have a different origin. We also find thatnearly half of these simulated halo clouds would be indistinguishable fromlower-velocity gas and that this effect is strongest further from the disk ofthe galaxy, thus indicating a possible missing population of HVCs. Theseresults indicate that the majority of HVCs are consistent with being infalling,condensed clouds that are a remnant of Galaxy formation.

Ongoing Galactic Accretion: Simulations and Observations of Condensed Gas in Hot Halos