We analyse X-ray data from the ASCA satellite for the galaxies NGC 4038/9 (also known as ‘the Antennae’), and find emission from both galaxies. At least two spectral components are required to describe the overall emission from these galaxies: thermal emission from a plasma at 0.8 keV, and a component at higher energies. The hot gas contributes about half of the flux in the 0.5- to 6-keV band. if the column density to the higher energy component is > 2 × 1021 cm−2 then the fitted abundance in the hot gas component is less than 0.2 times solar. This low abundance is not expected for the hot interstellar medium in NGC 4038/9 in which supernovae and star formation (expected to enrich and heat the gas) are ongoing. We do not detect any spatial variations in the spectrum. We relate these findings to data obtained by other X-ray satellites (Einstein,ROSAT) for this interacting galaxy pair.
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Sansom et al. (1996) studied this question.