Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21924413e&link_type=abstract
American Astronomical Society, AAS Meeting #219, #244.13
Astronomy and Astrophysics
Astronomy
Scientific paper
Giant star-formation clumps in dwarf irregular galaxies can have masses exceeding a few percent of the galaxy mass enclosed inside their orbital radii. They can produce sufficient torques on dark matter halo particles, halo stars, and the surrounding disk to lose their angular momentum and spiral into the center in less than 1 Gyr. Pairs of giant clumps with similarly large relative masses can interact and exchange angular momentum to the same degree. The result of this angular momentum loss is a growing central concentration analogous to a bulge in an earlier-type galaxy. A long history of inward migration will also produce a long-lived starburst in the inner regions as the gas column density remains above a threshold for star formation. Such a burst may be identified with the BCD phase in some dwarfs. Observations of giant star formation clumps in five local dwarf irregulars illustrate the relatively large clump masses that are suggested by this process. The observed clumps also seem to contain old field stars, even after background light subtraction, in which case they may be gravitationally bound and long-lived. The two examples with clumps closest to the center have the largest relative clump masses and the greatest contributions from old stars. This work was funded in part by the National Science Foundation through grants AST-0707563 and AST-0707426 to DAH and BGE. HZ was partly supported by NSF of China through grants #10425313, #10833006 and #10621303 to Professor Yu Gao.
Elmegreen Bruce
Hunter Deidre Ann
Zhang Huazhong
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