Velocity Dispersion, Mass, and the Luminosity Function of the Fossil Cluster RX J1416.4+2315

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Abstract
We study the properties of the fossil cluster RX J1416.4+2315 through g'- and i'-band imaging and spectroscopy of 25 member galaxies. The system is at a mean redshift of 0.137 and has a velocity dispersion of 584 km s-1. Superposed onto one quadrant of the cluster field is a group of five galaxies at a mean redshift of 0.131, which, if included as part of the cluster, increases the velocity dispersion to 846 km s-1. The central object of RX J1416.4+2315 is a normal elliptical galaxy with no cD envelope. The luminosity function of the system, estimated by the number counts and statistical background correction in the range -22.6 < M < -16.6, is well fitted by a Schechter function with M = -21.2 ± 0.8 and α = -1.2 ± 0.2 (H0 = 70 km s-1 Mpc-1, ΩM = 0.3, ΩΛ = 0.7). The luminosity function obtained from the spectroscopically confirmed members in both the g' and i' bands agrees with the photometric results. The mass of the system, M ~ 1.9 × 1014 h M⊙, its M/L of 445 h70 M⊙ L, and LX of 11 × 1043 h ergs s-1 (bolometric) suggest that this system is the second example of a known fossil cluster, after RX J1552.2+2013, confirmed in the literature.

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