X-ray emission from an expanding supergiant shell in IC 2574

We present a multiwavelength study of a supergiant shell within the violent interstellar medium of the nearby dwarf galaxy IC 2574, which is a member of the M81 group of galaxies. Neutral hydrogen (H I) observations obtained with the Very Large Array (VLA) reveal a prominent expanding supergiant H I shell in the northeast quadrant of IC 2574 which is thought to be produced by the combined effects of stellar winds and supernova explosions. It meas ures roughly 1000 x 500 pc in size and is expanding at similar to 25 km s(- 1). The H I data suggest an age of similar to 1.4 x 10(6) yr; the energy in put must have been of order (2.6 +/- 1) x 10(53) ergs. Massive star-forming regions, as traced by Hot emission, are situated predominantly on the rim of this H I shell. This supports the view that the accumulated H I on the r im has reached densities that are high enough for secondary star formation to commence. VLA radio continuum observations at lambda = 6 cm show that th ese star-forming regions are the main sources of radio continuum emission i n this galaxy. This emission is mainly thermal in origin. Soft X-ray emissi on from within the H I hole is detected by a pointed ROSAT PSPC observation . The emission is resolved, coinciding in size and orientation with the H I shell. These spatial properties suggest that the emission is generated by an X-ray-emitting plasma located within the H I shell, although a contribut ion from X-ray binaries cannot be completely ruled out. The X-ray luminosit y within the 0.11-2.4 keV energy range is L-x = (1.6 +/- 0.5) x 10(38) ergs s(-1). The X-ray data are compatible with emission coming from a Raymond-S mith plasma at a temperature of about log (T [K]) 6.8 and a density of n(e) similar to 0.03 cm(-3). The energy content of the coronal gas corresponds to (4 +/- 2) x 10(53) ergs, or broadly in agreement with the energy input d erived on the basis of the H 1 observations.