Spectral fits to X-ray data from both NGC 253 and M 82 provide ambiguousresults. The so-called ``best fit'' results depend on the instrument with whichthe data were obtained and obviously on the choice of spectral modelcomposition. We show that different spectral models can be fit equally well toBeppoSAX data of both galaxies. Metallicities are unreliable in general, with astrong dependence on the choice of model. Preference to one particular spectralmodel can only be given by combining spectroscopic and imaging X-ray data fromall available satellites (ROSAT, ASCA, and BeppoSAX). Based on spectra of NGC253, we demonstrate that a model consisting of two or more thermal plasmacomponents plus a hard power law continuum and Fe K alpha line emission canexplain all observations. These model components represent the integralspectrum of thermal gas and compact sources in starburst galaxies that are mostlikely supernova remnants and X-ray binaries. The same model can fit the X-raydata of M 82, but there the evidence, from ROSAT imaging, of the existence ofcompact sources which might represent high-mass X-ray binaries is weaker. Thisimplies that its hard X-ray emission, which is extended in ROSAT images, might- if truly diffuse - be dominated by a very hot (several keV energy) thermalgas component.
展开▼
