Abstract.We have observed the Virgo cluster spiral NGC 4569 in X-rays with ROSAT (0.1-2.4 keV) and in the optical. From the PSPC image one can distinguish different components, like the dominant source in the nuclear region, the galactic disk, and a diffuse soft component extended to the west. This latter one coincides with a giant Hα structure. In both spectral ranges the structure reaches up to 9 kpc out of the disk. This coincidence, the soft X-ray energy distribution, and the existence of a central starburst in NGC 4569 let us conclude that the X-ray gas traces a large scale outflow from accumulating supernova explosions and stellar winds in the galactic center. The resulting physical properties of this X-ray halo are comparable to those derived from X-ray halos in edge-on galaxies, like e.g. NGC 253. We also discuss the influence of the intracluster medium on the observed X-ray and Hα morphology. The spectral 0.1-2.4 keV distribution of the central source and the X-ray-to-Hα luminosity ratio favour a supermassive star cluster at the very compact core rather than an accretion-powered active nucleus in agreement with the absence of a hard compact X-ray source in the ASCA band. The nearby Magellanic dwarf galaxy IC 3583 at a projected distance of only 30 kpc reveals an unresolved X-ray point source, several blue knots in the optical, and a narrow Hα spur, pointing toward NGC 4569, detected also in the B band image. This is an indication for ongoing star formation also in IC 3583. Some interaction with NGC 4569 will be discussed although the relative radial velocity between both objects of about 1300 km s −1 makes it rather unlikely.

Abstract. In this paper we present ROSAT PSPC and HRI observations of the "hot-spot" 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 Hα 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 Hα results in 1-2 M 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 star-formation 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.

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