ROSAT observations of the IC 4329 A galaxy group ?

We report here the results of high-resolution and spectral imaging X-ray observations, with both the ROSAT HRI and PSPC, of the field surrounding the nearby (D = 64Mpc) type 1 Seyfert galaxy IC 4329A and its giant lenticular companion IC 4329. Many point sources are detected, the brightest being associated with IC 4329A itself, having an extremely bright X-ray luminosity of 6 × 1043 erg s−1, and spectral properties compatible with a single power-law model (Γ = 1.73), with a spectral break at 0.7 keV. Two other bright sources are detected associated with the companion galaxy IC 4329, and a likely quasar 14′ to the south-west. We have also established, through optical observations taken at the European Southern Observatory, that three further X-ray point sources, intriguingly positioned with respect to IC 4329A, are in fact nothing to do with the system, and are merely foreground and background objects. In addition to point source emission, residual, unresolved emission is detected surrounding the IC 4329A/ IC 4329 pair, extending for some 200 kpc. This emission appears markedly two-component, comprising of a spectrally hard and smooth component, circularly-distributed about the central galaxy pair, and a spectrally soft, more clumpy component, positioned almost entirely to the south-east of IC 4329A. The hard component of the residual emission itself appears two-component, one component being due to the ‘wings’ of the intensely bright IC 4329A source, the other, apparently due to hot (∼ 1.5 keV) gas, likely associated with the galaxy group of which IC 4329A and IC 4329 are members. The soft component of the residual emission may be a larger version of the superwinds seen around some ultraluminous far-infrared galaxies, or may even represent a ‘stripped wake’ of intragroup gas. Evidence for shocked gas due to the central IC 4329A/ IC4329 interaction is also found between the two central galaxies.