The SAMI Galaxy Survey: Quenching of Star Formation in Clusters III. Ram-Pressure-Affected Galaxy Populations

TL;DR

This study uses spatially resolved spectroscopy from the SAMI Galaxy Survey to identify and analyze galaxies affected by ram-pressure stripping in clusters, revealing how RPS influences star formation and galaxy evolution stages.

Contribution

It introduces a visual classification scheme for RPS-affected galaxies and links their gas morphology and star formation profiles to their evolutionary stage in cluster environments.

Findings

Asymmetric RPS galaxies are found in specific cluster regions with higher velocity dispersion.

RPS candidates show a steeper star-forming main sequence compared to unperturbed galaxies.

Star formation is suppressed in the outskirts of RPS galaxies, with central activity remaining similar to unperturbed counterparts.

Abstract

Cluster environments influence galaxy evolution by curtailing star formation activity, notably through ram-pressure stripping (RPS). In this study, using spatially resolved spectroscopic data from the SAMI Galaxy Survey, we identify galaxies undergoing or recently affected by RPS in eight nearby clusters ($0.029 < z < 0.058$), through a visual classification scheme based on the ionised gas ($\rm H\alpha + [NII]\lambda 6584$) morphologies, split into unperturbed, asymmetric, and truncated. The projected phase-space analysis shows that asymmetric galaxies are found in a narrow region in cluster-centric distance ($\rm 0.1 < R/R_{200} < 0.6$) and have a larger dispersion in line-of-sight velocity ($\sigma(|v_{pec}|)_\mathrm{Asym} = 0.71^{+0.09}_{-0.07}\ \sigma_{200}$) compared to the truncated and unperturbed samples. In terms of star formation activity, RPS candidates yield a much steeper resolved star-forming main sequence (rSFMS; $\Sigma_\mathrm{SFR} - \Sigma_\ast$) relation compared to the unperturbed counterparts, primarily emerging from having lower $\Sigma_\mathrm{SFR}$ values for the low mass density regime, with the steepest gradient deriving from the truncated sample. Moreover, radial star formation profiles reveal that star formation in RPS candidates is suppressed in the outskirts relative to unperturbed galaxies and is more prominent for the truncated sample. In contrast, central ($\rm r/r_{eff}<0.5$) star formation activity in RPS candidates is comparable with that in their unperturbed and field counterparts, suggesting no elevated activity. Taken together, this suggests an evolutionary trend linked to the RPS stage, where unperturbed galaxies likely represent recently accreted systems (pre-RPS), while asymmetric and truncated galaxies may correspond to populations undergoing RPS and post-RPS phases, respectively, favouring outside-in quenching.