X-Ray Tail in NGC 7619

Abstract

We present new observational results of NGC 7619, an elliptical galaxy with a prominent X-ray tail and a dominant member of the Pegasus group. With Chandra and XMM-Newton observations, we confirm the presence of a long X-ray tail in the southwest direction; moreover, we identify for the first time a sharp discontinuity of the X-ray surface brightness in the opposite (northeast) side of the galaxy. The density, temperature, and pressure jump at the northeast discontinuity suggest a Mach number ~1, corresponding to a galaxy velocity of ~500 km s^-1, relative to the surrounding hot gas. Spectral analysis of these data shows that the iron abundance of the hot gaseous medium is much higher (1-2 solar) near the center of NGC 7619 and in the tail extending from the core than in the surrounding regions (<=1/2 solar), indicating that the gas in the tail is originated from the galaxy. The possible origin of the head-tail structure is either ongoing ram pressure stripping or sloshing. The morphology of the structure is more in line with a ram pressure stripping phenomenon, while the position of NGC 7619 at the center of the Pegasus I group, and its dominance, would prefer sloshing.