The First Integral Field Unit Spectroscopic View of Shocked Cluster Galaxies

Galaxy clusters grow by merging with other clusters, giving rise to Mpc-wide shock waves that travel at 1000–2500 km s−1 through the intracluster medium. To study the effects of merger shocks on the properties of cluster galaxies, we present the first spatially resolved spectroscopic view of five Hα-emitting galaxies located in the wake of shock fronts in the low redshift (z ∼ 0.2), massive (∼2 × 1015M⊙), post-core passage merging cluster, CIZA J2242.8+5301 (nicknamed the "Sausage"). Our Gemini/Gemini Multi-Object Spectrograph-North integral field unit (IFU) observations, designed to capture Hα and [N ii] emission, reveal the nebular gas distribution, kinematics, and metallicities in the galaxies over >16 kpc scales. While the galaxies show evidence for rotational support, the flux and velocity maps have complex features like tails and gas outflows aligned with the merger axis of the cluster. With gradients that are incompatible with inside-out disk growth, the metallicity maps are consistent with sustained star formation (SF) throughout and outside of the galactic disks. In combination with previous results, these pilot observations provide further evidence of a likely connection between cluster mergers and SF triggering in cluster galaxies, a potentially fundamental discovery revealing the interaction of galaxies with their environment.