The Local Cluster Survey I: Evidence of Outside-In Quenching in Dense Environments

TL;DR

This study investigates how dense environments influence star-forming galaxies, revealing that outside-in quenching occurs over long timescales, leading to more centrally concentrated star formation as galaxies transition from gas-rich to gas-depleted states.

Contribution

It provides observational evidence for outside-in quenching in dense environments and constrains the timescale to over 2 Gyr, highlighting environmental mechanisms affecting galaxy evolution.

Findings

Galaxies in dense environments show more centrally concentrated star formation.

Transition from gas-rich to gas-depleted states correlates with increased central star formation.

Quenching occurs over timescales longer than 2 Gyr, consistent with outside-in mechanisms.

Abstract

The goal of the Local Cluster Survey is to look for evidence of environmentally driven quenching among star-forming galaxies in nearby galaxy groups and clusters. Quenching is linked with environment and stellar mass, and much of the current observational evidence comes from the integrated properties of galaxies. However, the relative size of the stellar and star-forming disk is sensitive to environmental processing and can help identify the mechanisms that lead to a large fraction of quenched galaxies in dense environments. Toward this end, we measure the size of the star-forming disks for 224 galaxies in nine groups and clusters (0.02<z<0.04; SFR > 0.1 M$_\odot$/yr) using 24um imaging from the Spitzer Space Telescope. We normalize the 24um effective radius (R24) by the size of the stellar disk (Rd). We find that star-forming galaxies with higher bulge-to-total ratios (B/T) and galaxies in more dense environments have more centrally concentrated star formation. Comparison with H~I mass fractions and NUV-r colors indicates that a galaxy's transition from gas-rich and blue to depleted and red is accompanied by an increase in the central concentration of star formation. We build a simple model to constrain the timescale over which the star-forming disks shrink in the cluster environment. Our results are consistent with a long-timescale (>2Gyr) mechanism that produces outside-in quenching, such as the removal of the extended gas halo or weak stripping of the cold disk gas.