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Head-on collisions: how to bring large quantities of gas out of inner disks

Published online by Cambridge University Press:  26 May 2016

Jonathan Braine ,
U. Lisenfeld  and
P.-A. Duc
Jonathan Braine
Affiliation:
Observatoire de Bordeaux, UMR 5804, CNRS/INSU, B.P. 89, F-33270 Floirac
U. Lisenfeld
Affiliation:
Instituto de Astrofísica de Andalucía, CSIC, Apdo. Correos 3004, 18080 Granada, Spain
P.-A. Duc
Affiliation:
CNRS URA 2052 and CEA/DSM/DAPNIA, Service d'Astrophysique, Saclay, 91191 Gif sur Yvette cedex, France

Abstract

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Head-on collisions of spiral galaxies can bring large quantities of gas out of spiral disks and into the intergalactic medium. Only two clear cases (UGC 12914/5 and UGC 813/6) of such collisions are known (Condon et al. 1993, 2002) and in both cases several 109 M⊙ of neutral gas is found in the bridge between the two galaxies which are now separating. About half of the gas is molecular. The gas, atomic or molecular, is brought out by collisions between clouds, which then acquire an intermediate velocity and end up between the galaxies. The bridges contain no old stars and in each case only one HII region despite the large masses of molecular gas, such that the star formation efficiency is very low in the bridges. The collisions occurred 20 – 50 million years ago, much greater than the collapse time for dense cores. We (Braine et al. 2003, 2004) show that collisions between molecular clouds, and not only between atomic gas clouds, bring gas into the bridges. It is not currently known whether the galaxies and bridges are bound or whether they will continue to separate, releasing several 109 M⊙ of neutral gas into the intergalactic medium.

Type
Part 3. Ejection and Outflow
Information
Symposium - International Astronomical Union , Volume 217: Recycling Intergalactic and Interslettar Matter , 2004 , pp. 420 - 421
Copyright
Copyright © Astronomical Society of the Pacific 2004 

References

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