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Published December 2010 | Published
Journal Article Open

Star Formation in Collision Debris: Insights from the Modeling of Their Spectral Energy Distribution

Abstract

During galaxy-galaxy interactions, massive gas clouds can be injected into the intergalactic medium which in turn become gravitationally bound, collapse, and form stars, star clusters, or even dwarf galaxies. The objects resulting from this process are both "pristine," as they are forming their first generation of stars, and chemically evolved because the metallicity inherited from their parent galaxies is high. Such characteristics make them particularly interesting laboratories in which to study star formation. After having investigated their star-forming properties, we use photospheric, nebular, and dust modeling to analyze their spectral energy distribution (SED) from the far-ultraviolet to the mid-infrared regime for a sample of seven star-forming regions. Our analysis confirms that the intergalactic star-forming regions in Stephan's Quintet, around Arp 105 and NGC 5291, appear devoid of stellar populations older than 10^9 years. We also find an excess of light in the near-infrared regime (from 2 μm to 4.5 μm) which cannot be attributed to stellar photospheric or nebular contributions. This excess is correlated with the star formation rate intensity suggesting that it is probably due to emission by very small grains fluctuating in temperature as well as the polycyclic aromatic hydrocarbons line at 3.3 μm. Comparing the attenuation via the Balmer decrement to the mid-infrared emission allows us to check the reliability of the attenuation estimate. It suggests the presence of embedded star-forming regions in NGC 5291 and NGC 7252. Overall the SED of star-forming regions in collision debris (and Tidal Dwarf Galaxies) resemble more that of dusty star-forming regions in galactic disks than to that of typical star-forming dwarf galaxies.

Additional Information

© 2010 The American Astronomical Society. Received 2010 March 17; accepted 2010 October 10; published 2010 November 12. We thank the anonymous referee for the useful comments that have helped improve and clarify this manuscript. U.L. acknowledges financial support by the Spanish Science Ministry under grant AYA 2007-67625-C02-02 and by the Junta de Andalucía. V.C. acknowledges partial support from the EU ToK grant 39965 and FP7-REGPOT 206469. Facilities: Akari, Spitzer, GALEX, CAO:2.2m, CFHT, ESO:3.6m, KPNO:2.1m, NTT

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