The First Integral Field Unit Spectroscopic View of Shocked Cluster Galaxies

TL;DR

This study uses integral field spectroscopy to analyze the impact of merger-induced shock waves on cluster galaxies, revealing complex gas dynamics and metallicity patterns that suggest merger-driven star formation.

Contribution

First spatially resolved spectroscopic observations of shock-affected cluster galaxies, linking merger shocks to star formation activity and gas kinematics.

Findings

Galaxies show complex gas tails and outflows aligned with merger axis.

Metallicity maps indicate sustained star formation outside galactic disks.

Evidence supports merger shocks triggering star formation in cluster galaxies.

Abstract

Galaxy clusters grow by merging with other clusters, giving rise to Mpc-wide shock waves that travel at 1000-2500 km/s through the intra-cluster medium. To study the effects of merger shocks on the properties of cluster galaxies, we present the first spatially resolved spectroscopic view of 5 H$\alpha$ emitting galaxies located in the wake of shock fronts in the low redshift (z~0.2), massive (~2$\times10^{15}$ M$_\odot$), post-core passage merging cluster, CIZA J2242.8+5301 (nicknamed the `Sausage'). Our Gemini/GMOS-N integral field unit (IFU) observations, designed to capture H$\alpha$ and [NII] 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 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.