# An isolated early-type dwarf galaxy that ran away from the group environment

## TL;DR

This paper reports the discovery of a quiescent early-type dwarf galaxy located in a nearly isolated environment, providing insights into galaxy quenching mechanisms outside dense groups.

## Contribution

It presents the first detailed analysis of an isolated quiescent dwarf galaxy likely ejected from a galaxy group, highlighting internal and environmental influences.

## Key findings

- The galaxy has a luminosity-weighted age of 8.3 Gyr.
- It has a subsolar metallicity of -1.19 dex.
- Its properties are consistent with classical quiescent dwarf ellipticals.

## Abstract

Understanding the quenching mechanisms in dwarf galaxies is crucial for constraining models of galaxy formation and evolution. In this vein, isolated dwarf galaxies offer valuable insight by helping disentangle the relative roles of internal and environmental processes in shutting down star formation. Here we report the discovery of a quiescent early-type dwarf galaxy (dE), SDSS J011754.86+095819.0 (hereafter dE01+09), located in a nearly isolated environment at a projected distance of approximately one megaparsec from its most likely host group, the NGC 524 group. dE01+09 has M_r = -15.72 and g-r = 0.67 mag and its light profile is well described by a S\'ersic function with an index n = 1.1, consistent with typical dEs. Using optical spectroscopy from the DESI survey, we derive its simple stellar population properties, finding an intermediate luminosity-weighted age of 8.3$\pm$1.4 Gyr and a subsolar metallicity of -1.19$\pm$0.21 dex -- characteristics comparable to those of classical quiescent dEs. We propose that NGC 524 may represent an extreme example of group dynamics, in which a member galaxy, dE01+09, is ejected from its host group and subsequently evolves as an isolated system in the field.