A Spectroscopic View of the JWST/GTO Strong Lensing Cluster A1489

Abstract: We discuss a spectroscopic survey of the strong lensing cluster A1489 that includes redshifts for 195 cluster members along with central velocity dispersions for 188 cluster members. The caustic technique applied to the redshift survey gives the dynamical parameters $M_{200} = (1.25~\pm~0.09) \times 10^{15}~M_\odot$, $r_{200} = 1.97~\pm~{0.05}$ Mpc, and a cluster line-of sight velocity dispersion $1150~\pm~{72}~$km$~$s$^{-1}$ within $r_{200}$. These parameters are very similar to those of other strong lensing systems with comparably large Einstein radii. We use the spectroscopy and deep photometry to demonstrate that A1489 is probably dynamically active; its four BCGs have remarkably different rest frame radial velocities. Like other massive strong lensing clusters, the velocity dispersion function for members of A1489 shows an excess for dispersions $\geq~250~$km$~$s$^{-1}$. The central dispersions also provide enhanced constraints on future lensing models.