A Stellar Mass Threshold for Quenching of Field Galaxies

TL;DR

This study reveals a stellar mass threshold of 10^9 Msun below which dwarf galaxies in the field are almost never quenched, emphasizing the role of environment in galaxy evolution.

Contribution

It identifies a clear stellar mass threshold for quenching in field dwarf galaxies and highlights the environmental dependence of galaxy quenching processes.

Findings

Quenched dwarf galaxies are extremely rare (<0.06%) in the field below 10^9 Msun.

The fraction of quenched dwarfs increases near massive hosts and drops to near zero beyond 1.5 Mpc.

Most quenched dwarfs are within 2 virial radii of a massive galaxy.

Abstract

We demonstrate that dwarf galaxies (10^7 < M_stellar < 10^9 Msun) with no active star formation are extremely rare (<0.06%) in the field. Our sample is based on the NASA-Sloan Atlas which is a re-analysis of the Sloan Digital Sky Survey Data Release 8. We examine the relative number of quenched versus star forming dwarf galaxies, defining quenched galaxies as having no Halpha emission (EW_Halpha < 2 AA) and a strong 4000AA-break. The fraction of quenched dwarf galaxies decreases rapidly with increasing distance from a massive host, leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of a massive host galaxy to be in the field. We demonstrate that there is a stellar mass threshold of M_stellar < 1.0x10^9 Msun below which quenched galaxies do not exist in the field. Below this threshold, we find that none of the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show evidence for recent star formation. Correcting for volume effects, this corresponds to a 1-sigma upper limit on the quenched fraction of 0.06%. In more dense environments, quenched galaxies account for 23% of the dwarf population over the same stellar mass range. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii. Thus, for galaxies with stellar mass less than 1.0x10^9 Msun, ending star-formation requires the presence of a more massive neighbor, providing a stringent constraint on models of star formation feedback.