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Title:
Ongoing Galactic Accretion: Simulations and Observations of Condensed Gas in Hot Halos
Authors:
Peek, J. E. G.; Putman, M. E.; Sommer-Larsen, Jesper
Affiliation:
AA(Department of Astronomy, University of California, Berkeley, CA 94720.), AB(Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109.), AC(Dark Cosmology Centre, Niels Bohr Institute, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark.; Institute of Astronomy, University of Tokyo, Osawa 2-21-1, Mitaka, Tokyo, 181-0015, Japan.)
Publication:
The Astrophysical Journal, Volume 674, Issue 1, pp. 227-236. (ApJ Homepage)
Publication Date:
02/2008
Origin:
UCP
ApJ Keywords:
Galaxies: Formation, Galaxy: Halo, ISM: Clouds, ISM: Kinematics and Dynamics
DOI:
10.1086/524374
Bibliographic Code:
2008ApJ...674..227P

Abstract

Ongoing accretion onto galactic disks has been recently theorized to progress via the unstable cooling of the baryonic halo into condensed clouds. These clouds have been identified as analogous to the high-velocity clouds (HVCs) observed in H I in our Galaxy. Here we compare the distribution of HVCs observed around our own Galaxy and extraplanar gas around the Andromeda galaxy to these possible HVC analogs in a simulation of galaxy formation that naturally generates these condensed clouds. We find a very good correspondence between these observations and the simulation in terms of number, angular size, velocity distribution, overall flux, and flux distribution of the clouds. We show that condensed cloud accretion accounts for only ~0.2 Msolar yr-1 of the current overall Galactic accretion in the simulations. We also find that the simulated halo clouds accelerate and become more massive as they fall toward the disk. The parameter space of the simulated clouds is consistent with all of the observed HVC complexes that have distance constraints, except the Magellanic Stream, which is known to have a different origin. We also find that nearly half of these simulated halo clouds would be indistinguishable from lower velocity gas and that this effect is strongest farther from the disk of the galaxy, thus indicating a possible missing population of HVCs. These results indicate that the majority of HVCs are consistent with being infalling, condensed clouds that are a remnant of Galaxy formation.
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