Chandra observation of two shock fronts in the merging galaxy cluster Abell 2146
Fabian, A. C.; McNamara, B. R.; Russell, H. R.; Edge, A. C.; Sanders, J. S.; Donahue, M.; O'Dea, C. P.; Baum, S. A.
United Kingdom, United States, Canada
Abstract
We present a new Chandra observation of the galaxy cluster Abell 2146 which has revealed a complex merging system with a gas structure that is remarkably similar to the Bullet cluster. The X-ray image and temperature map show a cool 2 -3 keV subcluster with a ram pressure stripped tail of gas just exiting the disrupted 6 - 7 keV primary cluster. From the sharp jump in the temperature and density of the gas, we determine that the subcluster is preceded by a bow shock with a Mach number M = 2.2 +/- 0.8, corresponding to a velocity v = 2200+1000-900 kms-1 relative to the main cluster. We estimate that the subcluster passed through the primary core only 0.1 -0.3 Gyr ago. In addition, we observe a slower upstream shock propagating through the outer region of the primary cluster and calculate a Mach number M = 1.7 +/- 0.3. Based on the measured shock Mach numbers M ~ 2 and the strength of the upstream shock, we argue that the mass ratio between the two merging clusters is between 3 and 4 to one. By comparing the Chandra observation with an archival Hubble Space Telescope observation, we find that a group of galaxies is located in front of the X-ray subcluster core but the brightest cluster galaxy is located immediately behind the X-ray peak.