Galaxy Evolution in the Cluster Abell 85: New Insights from the Dwarf Population

TL;DR

This study presents a spectroscopic survey of the galaxy cluster Abell 85, revealing the properties and evolution of its dwarf galaxy population, star formation activity, and evidence for rapid quenching mechanisms like ram-pressure stripping.

Contribution

It provides the first detailed spectroscopic analysis of Abell 85's dwarf galaxies and their star formation evolution, highlighting environmental effects and quenching timescales.

Findings

Dwarf galaxies constitute 25% of the sample, with median stellar mass $10^{9.6} M_{\odot}$.

Star formation activity increases with distance from the cluster center.

Evidence suggests rapid quenching mechanisms such as ram-pressure stripping are dominant.

Abstract

We present the first results of a new spectroscopic survey of the cluster Abell 85 targeting 1466 candidate cluster members within the central $\sim$1 deg$^2$ of the cluster and having magnitudes $m_r < 20.5$ using VIMOS/VLT and HYDRA/WIYN. A total of 520 galaxies are confirmed as either relaxed cluster members or part of an infalling population. A significant fraction are low mass; the median stellar mass of the sample is $10^{9.6} M_{\odot} $, and 25% have stellar masses below $10^9 M_{\odot}$ (i.e. 133 dwarf galaxies). We also identify seven active galactic nuclei (AGN), four of which reside in dwarf host galaxies. We probe the evolution of star formation rates, based on H$\alpha$ emission and continuum modeling, as a function of both mass and environment. We find that more star forming galaxies are observed at larger clustercentric distances, while infalling galaxies show evidence for recently enhanced star forming activity. Main sequence galaxies, defined by their continuum star formation rates, show different evolutionary behavior based on their mass. At the low mass end, the galaxies have had their star formation recently quenched, while more massive galaxies show no significant change. The timescales probed here favor fast quenching mechanisms, such as ram-pressure stripping. Galaxies within the green valley, defined similarly, do not show evidence of quenching. Instead, the low mass galaxies maintain their levels of star forming activity, while the more massive galaxies have experienced a recent burst.