A Chandra X-ray survey of nearby dwarf starburst galaxies: II. Starburst   properties and outflows
  (abridged) We present a comprehensive comparison of the X-ray properties of a sample of eight dwarf starburst galaxies observed with Chandra (I Zw 18, VII Zw 403, NGC 1569, NGC 3077, NGC 4214, NGC 4449, NGC 5253, He 2-10). In Paper I we presented in detail the data reduction and analysis of the individual galaxies. For the unresolved X-ray sources we find the following: point sources are in general located close to bright HII regions, rims of superbubbles, or young stellar clusters. The number of X-ray point sources appears to be a function of the current star formation rate and the blue luminosity of the hosts. Ultraluminous X-ray sources are only found in those dwarf galaxies which are currently interacting. The power law index of the combined cumulative X-ray point source luminosity function is alpha=0.24+/-0.06, shallower than that of more massive starburst galaxies (alpha=0.4-0.8) and of non-starburst galaxies (alpha~1.2). For those galaxies showing extended X-ray emission (6 out of the 8 galaxies), we derive the following: Superwinds develop along the steepest gradient of the HI distribution with volume densities of 0.02-0.06 cm^-3, pressures of 1-3x10^5 K cm^-3, thermal energies of 2-30x10^54 erg, and hot gas masses of 2-20x10^6 Mo (~1 per cent of the HI masses). The mechanical luminosities of the developing superwinds are energetic enough to overcome the gravitational potentials of their host galaxies. This scenario is supported by the overpressures of the hot gas compared to the ambient ISM. Extended HI envelopes such as tidal tails, however, may delay outflows on timescales exceeding those of the cooling time of the hot gas. 
Juergen Ott, Fabian Walter, and Elias Brinks