THE NEXT GENERATION VIRGO CLUSTER SURVEY. XIV. Shell feature early-type dwarf galaxies in the Virgo cluster

TL;DR

This study reports the discovery of faint shell features in three Virgo cluster dwarf galaxies, including the least massive galaxy with such features, and suggests they formed from recent near-equal mass mergers based on observations and simulations.

Contribution

First detection of shell features in extremely faint dwarf galaxies in the Virgo cluster, supported by simulations indicating recent mergers as their origin.

Findings

Shell features found in three dwarf galaxies, including the least massive with such features.

Shells are symmetric and aligned with the galaxy major axis.

Simulations suggest recent near-equal mass mergers produce observed shells.

Abstract

The Next Generation Virgo Cluster Survey is a deep (with a $2\sigma$ detection limit $\mu_g$ = 29~mag~arcsec$^{-2}$ in the $g-$band) optical panchromatic survey targeting the Virgo cluster from its core to virial radius, for a total areal coverage of 104 square degrees. As such, the survey is well suited for the study of galaxies' outskirts, haloes and low surface brightness features that arise from dynamical interactions within the cluster environment. We report the discovery of extremely faint ($\mu_g$ $>$ 25 mag arcsec$^{-2}$) shells in three Virgo cluster early-type dwarf galaxies, VCC~1361, VCC~1447 and VCC~1668. Among them, VCC~1447 has an absolute magnitude M$_{g}$ = -11.71 mag and is {\it the least massive galaxy with a shell system discovered to date}. We present a detailed study of these low surface brightness features. We detect between three and four shells in each of our galaxies. Within the uncertainties, we find no evidence of a color difference between the galaxy main body and shell features. The observed arcs of the shells are located upto several effective radii of the galaxies. We further explore the origin of these low surface brightness features with the help of idealized numerical simulations. We find that a near equal mass merger is best able to reproduce the main properties of the shells, including their quite symmetric appearance and their alignment along the major axis of the galaxy. The simulations provide support for a formation scenario in which a recent merger, between two near-equal mass, gas-free dwarf galaxies forms the observed shell systems.