A Dynamical Analysis of the Poor Galaxy Clusters Abell 2626 and Abell 2440

We use 189 new radial velocities and R band CCD photometry to study the galaxy clusters Abell 2626 and Abell 2440. By combining these new optical constraints with archival x-ray images and gas temperature measurements, we investigate the dynamical nature of both systems. We derive masses, luminosity functions, and mass-to-light ratios. The symmetric x-ray emission from A2626 suggests a relaxed, single-component system; however, our sample of 159 redshifts reveals a complex, three-component cluster at cz ~ 17500 km/s. One of these components is a typical x-ray bright cluster, a second has a cluster-like galaxy population with a much lower central galaxy and gas density, and the third is a background structure with field galaxy composition. A comparison of the magnitude distributions within the two subclusters suggests that A2626 is a merger in progress (at 93% confidence). Virial masses and a composite luminosity function for a region with projected radius r= 1.5h^-1^ Mpc yield a mass- to-light ratio M/L_R_ ~ 610h. Analysis of the x-ray emission from the primary component yields a gas mass function of ~2.2h^-3/2^% and a baryon fraction of ~3.4%. A radial infall model indicates that the virial mass may be an underestimate. The bimodal x-ray emission and elongated galaxy distribution of A2440 have been studied before (Baier 1979; Beers et al. 1991). With deeper, CCD R band photometry we demonstrate a striking correspondence between the galaxy and cluster gas distributions. The galaxy distribution has three main components, each associated with a giant elliptical galaxy. The two larger peaks in the galaxy distribution coincide with the primary peaks in the x-ray emission, and the third is associated with a significant x-ray surface brightness enhancement. We use this galaxy-gas correspondence, 48 redshifts, and the structure of the x-ray emission to argue that the subclusters are bound within a single system, and that the two primary components are beginning to merge. The composite luminosity function and estimates of the subcluster virial masses indicate a mass-to-light ratio in the range M/L_R_ = 660h to 880h.