A large-scale kinematic study of molecular gas in high-z cluster galaxies: Evidence for high levels of kinematic asymmetry

TL;DR

This study uses ALMA to analyze the molecular gas kinematics in 25 high-redshift cluster galaxies, revealing high levels of kinematic asymmetry likely driven by environmental interactions, marking a significant step in understanding galaxy evolution in dense environments.

Contribution

First large-scale analysis of molecular gas kinematics in high-redshift cluster galaxies, highlighting environmental effects on galaxy dynamics at z~1.6.

Findings

Majority of galaxies show high kinematic asymmetry compared to field galaxies.

Some galaxies exhibit asymmetry up to 50 times higher than in the field.

Evidence of tidal and ram pressure interactions affecting galaxy kinematics.

Abstract

We investigate the resolved kinematics of the molecular gas, as traced by ALMA in CO (2-1), of 25 cluster member galaxies across three different clusters at a redshift of $z\sim1.6$. This is the first large-scale analysis of the molecular gas kinematics of cluster galaxies at this redshift. By separately estimating the rotation curve of the approaching and receding side of each galaxy via kinematic modeling, we quantify the difference in total circular velocity to characterize the overall kinematic asymmetry of each galaxy. 3/14 of the galaxies in our sample that we are able to model have similar degrees of asymmetry as that observed in galaxies in the field at similar redshift. However, this leaved 11/14 galaxies in our sample with significantly higher asymmetry, and some of these galaxies have degrees of asymmetry of up to $\sim$50 times higher than field galaxies observed at similar redshift. Some of these extreme cases also have one-sided tail-like morphology seen in the molecular gas, supporting a scenario of tidal and/or ram pressure interaction. Such stark differences in the kinematic asymmetry in clusters versus the field suggest the evolutionary influence of dense environments, established as being a major driver of galaxy evolution at low-redshift, is also active in the high-redshift universe.