The Fundamental Plane in RX J0142.0+2131: A Galaxy Cluster Merger at [FORMULA][F]z=0.28[/F][/FORMULA]

Abstract

We present the fundamental plane (FP) in the z = 0.28 cluster of galaxies RX J0142.0+2131. There is no evidence for a difference in the slope of the FP when compared with the Coma Cluster, although the internal scatter is larger. On average, stellar populations in RX J0142.0+2131 have rest-frame V-band mass-to-light ratios (MIL v ) 0.29 ± 0.03 dex lower than in Coma. This is significantly lower than expected for a passively evolving cluster formed at z f = 2. Lenticular galaxies have lower average M/L v and a distribution of M/L v with larger scatter than ellipticals. Lower mass-to-light ratios are not due to recent star formation: our previous spectroscopic observations of RX J0142.0+2131 E/S0 galaxies showed no evidence for significant star formation within the past ∼4 Gyr. However, cluster members have enhanced α-element abundance ratios, which may act to decrease M/L v . The increased scatter in the RX J0142.0+2131 FP reflects a large scatter in M/L v implying that galaxies have undergone bursts of star formation over a range of epochs. The seven easternmost cluster galaxies, including the second brightest member, have M/L v consistent with passive evolution and z f = 2. We speculate that RX J0142.0+2131 is a cluster-cluster merger where the galaxies to the east are yet to fall into the main cluster body or have not experienced star formation as a result of the merger. © 2006. The American Astronomical Society. All rights reserved.