Unravelling the orbits of cluster galaxy populations according to their dominant gas ionization source

TL;DR

This study analyzes the kinematic and dynamical properties of different galaxy populations in clusters based on their dominant gas ionization source, revealing their orbital behaviors and equilibrium states.

Contribution

It provides a detailed comparison of galaxy populations classified by ionization source, using advanced modeling to understand their orbital anisotropies and dynamical states within clusters.

Findings

Quiescent galaxies are closest to cluster centers with lowest velocity dispersion.

Star-forming galaxies are more distant and have higher velocity dispersion.

AGN host galaxies show intermediate properties between star-forming and quiescent populations.

Abstract

We investigate the kinematical and dynamical properties of cluster galaxy populations classified according to their dominant source of gas ionization, namely: star-forming (SF) galaxies, optical active galactic nuclei (AGN), mixed SF plus AGN ionization (transition objects, T), and quiescent (Q) galaxies. We stack 8892 member galaxies from 336 relaxed galaxy clusters to build an ensemble cluster and estimate the observed projected profiles of numerical density and velocity dispersion, $\sigma_P(R)$, of each galaxy population. The MAMPOSSt code and the Jeans equations inversion technique are used to constrain the velocity anisotropy profiles of the galaxy populations in both parametric and non-parametric ways. We find that Q (SF) galaxies display the lowest (highest) typical cluster-centric distances and velocity dispersion values. Transition galaxies are more concentrated and tend to exhibit lower velocity dispersion values than SF galaxies. Galaxies that host an optical AGN are as concentrated as Q galaxies but display velocity dispersion values similar to those of the SF population. MAMPOSSt is able to find equilibrium solutions that successfully recover the observed $\sigma_P(R)$ profile only for the Q, T, and AGN populations. We find that the orbits of all populations are consistent with isotropy in the inner regions, becoming increasingly radial with the distance from the cluster centre. These results suggest that Q galaxies are in equilibrium within their clusters, while SF galaxies have more recently arrived in the cluster environment. Finally, the T and AGN populations appear to be in an intermediate dynamical state between those of the SF and Q populations.