An X-ray halo in the "hot-spot" galaxy NGC 2903

In this paper we present ROSAT PSPC and HRI observations of the "hotspot" galaxy NGC 2903. This isolated system strikingly reveals a soft extended X-ray feature reaching in north-west direction up to a projected distance of 5.2 kpc from the center into the halo. The residual X-ray emission in the disk reveals the same extension as the H (alpha)disk. No eastern counterpart of the western X-ray halo emission has been detected. The luminosity of the extraplanar X-ray gas is several 10^38 erg s ^-1, comparable to X-ray halos in other starburst galaxies. It has a plasma temperature of about 0.2 keV. The estimated star formation rate derived from X-rays and H (alpha)results in 1-2  M(circled dot operator) yr^ -1. Since galactic superwinds, giant kpc-scale galactic outflows, seem to be a common phenomenon observed in a number of edge-on galaxies, especially in the X-ray regime, and are produced by excess starformation activity, the existence of hot halo gas as found in NGC 2903 can be attributed to events such as central starbursts. That such a starburst has taken place in NGC 2903 must be proven. The detection of hot gas above galaxy disks also with intermediate inclination, however, encounters the difficulty of discriminating between that contribution from disk and active nuclear region.