A high-resolution ROSAT X-ray study of the Hercules cluster

The well-studied, irregular Hercules cluster of galaxies (Abell 2151) was observed in X-rays with the ROSAT HRI. We find that the X-ray emission is concentrated toward the central subcluster of the system, in agreement with previous Einstein and ROSAT PSPC observations. The X-ray emission in this subcluster divides into two components, which correspond to two groups of galaxies in the region. The center of the brightest (western) X-ray component coincides with the brightest cluster galaxy (BCG) NGC 6041A, while there is an X-ray peak near the center of the poorer eastern component that agrees with the position of an elliptical radio galaxy NGC 6047. The X-ray emission is fairly irregular, and there are separate X-ray features associated with individual galaxies including the BCG NGC 6041A. There are two X-ray clumps associated with an interacting peculiar galaxy pair NGC 6040A/B. Gas stripping from the galaxy pair has depleted about 80% of their neutral hydrogen contents. In addition, the stripped gas may constitute a majority of the X-ray emitting gas in this region, which suggests that the gas stripping in this subcluster may be very efficient and is an important contributing factor to the origin of the hot gas. The interaction of the intracluster gas with the radio galaxy NGC 6047 has also been investigated. A cooling flow of M = 143 +/- 28 M(.) yr(-1) is found in the central subcluster that may have deposited a significant fraction of the cooled gas to the central BCG galaxy NGC 6041A. We also probed the dynamic structure and dark matter distribution in the central subcluster. Our data show that, within the central 678 kpc, total dark matter in this main subcluster is comparable to the total material contained in luminous galaxies and X-ray emitting gas in the region. Throughout the paper, we have assumed a Hubble constant of 50 km s(-1) Mpc(-1) and q(0) = 0.5.