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D.K. Strickland (Johns Hopkins University), I.R. Stevens (University of Birmingham)
Supernovae and stellar winds from the massive stars in a starburst galaxy are believed to form an expanding superbubble of hot X-ray emitting gas, eventually leading to a galactic ``superwind'' of hot, metal-enriched gas and swept-up ISM that may escape the host galaxy completely.
Such outflows are particularly interesting in dwarf galaxies, as due to their shallow gravitational potential wells a starburst-driven wind could eject a substantial fraction of their ISM. In principle X-ray observations provide a direct probe of the hot SN-enriched gas driving these superbubbles and galactic winds. Indeed, ROSAT PSPC observations of local starbursting dwarf galaxies reveal soft thermal X-ray emission, usually assumed to be due to young superbubbles. The PSPC's spatial resolution is not good enough to resolve this X-ray emission, so it is by no means clear that the picture described above is correct.
We report on a long ROSAT HRI observation of the nearby dwarf starburst and Wolf-Rayet galaxy NGC 5253. Instead of a single superbubble, we find a complex of at least five sources of X-ray emission associated with the young massive star clusters at the centre of NGC 5253. We argue that the majority of the soft X-ray emission from NGC 5253 comes from a few young superbubbles blown by these young stellar clusters.
We suggest the presence of multiple stellar clusters in starbursting dwarf galaxies, and the resulting multiple superbubbles, will reduce the total ISM mass ejected from from dwarf galaxies compared to the current theoretical models which only consider the blowout of a single superbubble.
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