H-Band and Spectroscopic Properties of Abell 1644

Abstract

We discuss H-band (1.65 micrometer) near-infrared photometry of the central 3x3h^{-2} Mpc^2 of Abell 1644 to a limiting M_H~M^*_H+3 (throughout this paper H_0=100 h km s^{-1} Mpc^{-1}). There are 861 galaxies in the photometric survey region. We also measured radial velocities of 155 galaxies; 141 of these are cluster members within 2.44 h^{-1} Mpc of the cluster center. The cluster velocity dispersion of sigma~1000 km s^{-1} remains constant out to the limiting radius. We find no evidence for substructure in the cluster. The cluster mass within R=2.4 h^{-1} Mpc is 7.6+-1.3x10^{14} h^{-1} M_\odot. We compute the cluster luminosity function; the Schechter parameters α=-1.14\pm0.08 and M^*_H=-24.3\pm0.2 (with h=0.5) agree well with other H-band luminosity functions. From the virial theorem and the caustic method we compute one of the first mass-to-light ratios at H; the result is M/L_H=82-127 h M_\odot/L_\odot within 1.5 h^{-1} Mpc. This ratio corresponds to 374-579 h M_\odot/L_\odot at R. The agreement of our IR measurement with previous $M/L$ determinations indicates that at low redshift dust and young stellar populations may produce only negligible systematic errors in optical mass-to-light ratios.