2006A&A...457..779T

In a previous paper (PaperI) we showed that multi-phase gaseous halos of late-type spiral galaxies, detected in the radio continuum, in Hα, and in X-rays, are remarkably well correlated regarding their morphology and spatial extent. In this work we present new results from a statistical analysis to specify and quantify these phenomenological relations in more detail. This is accomplished by investigating soft X-ray (0.3-2.0keV) luminosities, FIR, radio continuum (1.4GHz), Hα, B-band, and UV (1550-1650Å) luminosities for a sample of 23 edge-on late-type spiral galaxies. Typical star formation indicators, such as star formation rates (SFRs), are determined and a statistical multi-parameter/frequency correlation analysis is carried out. We find strong linear correlations, covering at least two orders of magnitude, between star formation indicators and integrated (disk+halo) luminosities in all covered wavebands. In addition to the well-established L_FIR/L_1.4GHz relation, we show new and highly significant linear dependencies between integrated soft X-ray luminosities and FIR, radio continuum, Hα, B-band, and UV luminosities. Moreover, integrated soft X-ray luminosities correlate well with SFRs and the energy input into the ISM by SNe. The same holds if these quantities are plotted against soft halo X-ray luminosities. Only a weak correlation exists between the dust mass of a galaxy and the corresponding X-ray luminosity. Among soft X-ray luminosities, baryonic, and HI gas masses, no significant correlations are found. There seems to exist a critical input energy by SNe into the ISM or a SFR threshold for multi-phase halos to appear. It is still not clear whether this threshold is a physical one or represents an instrument-dependent sensitivity limit. These findings strongly support our previous results that multi-phase gaseous galaxy halos in late-type spiral galaxies are created and maintained by outflowing gas produced in star formation processes in the disk plane. They conflict with the concept of halos being mainly due to infalling gas from the intergalactic medium.