ABSTRACT

We report the results of ROSAT PSPC observations of two merging galaxy systems. The nearest classic example, the Antennae, shows X-ray features alt the two galactic nuclei, together with features interpreted as large H II regions, all embedded in apparently diffuse emission. Another feature with no radio or optical counterparts may be a hot outflow. NGC 2623, a more infrared-luminous system, is at a later merger stage. Although less X-ray lumiiious than the Anteniiae, it has a hotter nuclear feature, and a larger outflow. Thesfc observations are part of a chronological sequence of merging galaxies, carefully chosen in order to study the evolution of their X-ray properties through the merging process. These early results suggest that, as a rrierger progresses, the X-ray emission may evolve more rapidly than the infrared, and that massive hot outflows are generated.

INTRODUCTION AND OBSERVATIONS

Although merging galaxies have been the subject of intensive multiwavelength studies, particularly over the past decade, studies in the X-ray band have been severely restricted by the limited spatial resolution and sensitivity of instrumentation available. The best study prior to the launch of ROSAT was the Einstein IPC observation of the Antennae, which produced interesting but inconclusive results.

We are studying the X-ray development of merging galaxies at different stages of coalescence. ROSAT PSPC results for two such systems are presented here.

The Antennae, NGC 4038/9 (Arp 244), has much multi-wavelength information available. It is one of the closest merging systems (hence both large and bright) and its classic two-tailed form makes the presence of an interaction unambiguous.