The million-degree interstellar medium in spiral galaxies

We searched for a million-degree interstellar medium in the disks and halos of ten spiral galaxies. The sample, observed with ROSAT, contains starburs ts, galaxies harboring AGNs and quiescent galaxies. The existence of hot ga s was established for seven galaxies: NGC 253, NGC 1566, NGC 3079, NGC 4258 , NGC 4449, NGC 4565 and NGC 4631. With the exception of NGC 4565, these ga laxies show enhanced star formation or/and host AGUs. From the derived X-ra y luminosity and temperature, we calculated the density and mass of the hot gas components. For the nuclear regions of NGC 253 and NGC 3079, as well a s for the hot interstellar medium along the anomalous spiral arms of NGC 42 58, the densities are greater than or similar to 10(-2) cm(-3), while n sim ilar to 10(-3) cm(-3) for the gas in the halos of the galaxies. We discuss the findings in the framework of models describing the formation of hot int erstellar medium in the disk and its outflow into the halo and compare our sample to other galaxies.