THE DETECTION OF THE HOT GASEOUS HALO AROUND THE SMALL MAGELLANIC CLOUD

We report the detection of diffuse X-ray emission from the vicinity of the Small Magellanic Cloud. The diffuse emission constitutes about 60% of the total observed X-ray flux in a 0.16-3.5 keV band from a field mapped out with the Einstein imaging proportional counter, and extends beyond the active main body of the galaxy, suggesting substantial emission from the galaxy's halo. The emission spectrum, getting soft away from the main body, is consistent with a picture in which hot gas, created in recent star formation regions, cools off on the way out into the halo. While the total observed luminosity of the diffuse X-rays is only 10(38.7) ergs s-1 in the 0.16-3.5 keV band, the low temperature (less-than-or-similar-to 10(6) K) of the X-ray-emitting gas implies that its total cooling rate could be sufficient in balancing the supernova heating in the galaxy. The bulk of the radiation should be in a spectral range from EUV to extreme soft X-ray. It is speculated that a similar picture may also hold for the energy budget evolution in our Galaxy, and a general scenario is described for the dynamic and thermal evolution of hot gas blowing out from the disk plane into the halo of a galaxy.