A ROSAT PSPC study of NGC 55

Abstract

The Position Sensitive Proportional Counter onboard ROSAT imaged the spiral galaxy NGC 55 in X-rays for 18.9 ksec. Twenty-two point-like X-ray sources are detected covering the PSPC field-of-view, of which 7 sources are candidate members of NGC 55. The spectra of the brightest sources that are nearest to NGC 55 are consistent either with a heavily absorbed source or a foreground star. The absorbed sources are very likely members of NGC 55. None of the brightest sources appear to be variable in a periodic fashion. Weak diffuse emission is detected in the plane of the galaxy, but only in the energy bands above ~0.5 keV. This emission is either the tail of a hot component of the ISM or the emission of unresolved point sources. We argue that the emission is a hot ISM component. A hot plume, visible in the 0.75 keV band, appears to align with an H I plume detected in a VLA total H I map. The cool H I gas appears to surround the hot gas, so the structure represents a chimney.