An Interaction Model for the Formation of Dwarf Galaxies and 10(8) Msun Clouds in Spiral Disks

Details An Interaction Model for the Formation of Dwarf Galaxies and 10(8) Msun Clouds in Spiral Disks An Interaction Model for the Formation of Dwarf Galaxies and 10(8) Msun Clouds in Spiral Disks

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.9206e&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #92.06; Bulletin of the American Astronomical Society, Vol. 24, p.1267

Astronomy and Astrophysics

Astronomy

Scientific paper

Galaxy interactions that agitate the interstellar medium by increasing the gas velocity dispersion and removing peripheral gas in tidal arms should lead to the formation and possible ejection of self-gravitationally bound cloud complexes with masses in excess of 10(8) Msun. Some of these complexes may eventually appear as independent dwarf galaxies. The formation of clouds with masses exceeding 10(8) Msun is the result of gravitational instabilities in gas disks with high velocity dispersions. Such masses and high dispersions were observed with the VLA for the interacting pair IC 2163/NGC 2207, which contains 10 clouds with HI masses >10(8) Msun and widespread velocity dispersions 4 times larger than in normal spiral galaxies. A giant cloud that forms by an instability in a high-dispersion ISM should also have a high internal dispersion, and it should produce stars with a greater efficiency than in normal galaxies because of the cloud's greater resistance to self-destruction. Such clouds should also have a larger fraction of massive stars than normal clouds because of the larger temperatures that follow from the high efficiency. Thus agitated galaxies should produce peripheral or nuclear starbursts partly because of their high gas velocity dispersions. Numerical N-body simulations of interacting galaxies illustrate the proposed formation of 10(8) Msun cloud complexes by gravitational instabilities. The masses and dispersions of the clouds that form increase with the strength of the perturbation. The simulations suggest that the complete detachment of an unbound dwarf galaxy requires a companion mass comparable to or larger than the galaxy mass. Dwarf galaxies that form this way should contain old stars from the original disk plus new stars from the cloud complex/starburst phase of its interaction-induced formation. This work was supported in part by NSF Grant AST-8914969 to M.K..

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