On the accretion of a new group of galaxies onto Virgo: I. Internal kinematics of nine in-falling dEs

TL;DR

This study examines nine dwarf galaxies recently accreted onto the Virgo cluster to understand how their kinematics reveal the influence of their past host halos versus the current cluster environment.

Contribution

It provides the first detailed kinematic analysis of a unique group of dwarf galaxies accreted onto Virgo, distinguishing effects of prior host halos from the current cluster environment.

Findings

Half of the dwarf galaxies have high angular momentum profiles similar to field galaxies.

The other half show low angular momentum, indicating prior processing by their previous host halos.

Detection of ongoing gas stripping in one galaxy suggests active environmental effects.

Abstract

Galaxy environment has been shown to play an important role in transforming late-type, star-forming galaxies to quiescent spheroids. This transformation is expected to be more severe for low-mass galaxies (M < $10^{10}$ \(M_\odot\)) in dense galaxy groups and clusters, mostly due to the influence of their past host halos (also known as pre-processing) and their present-day environments. For the first time, in this study, we investigate a sample of nine early-type dwarf galaxies (dEs) that were accreted as a likely bound group onto the Virgo galaxy cluster about 2-3 Gyr ago. Considering this special condition, these nine dEs may provide a test bed for distinguishing between the influence of the Virgo galaxy cluster and the effects of the previous host halo on their current properties. Specifically, we use VLT/MUSE integral-field unit spectra to derive their kinematics and specific angular momentum ($\lambda_{R}$) profiles. We observe a spread in the $\lambda_{R}$ profiles of our sample dEs, finding that the $\lambda_{R}$ profiles of half of them are as high as those of low-mass field galaxies. The remaining dEs exhibit $\lambda_{R}$ profiles as low as those of Virgo dEs that were likely accreted longer ago. Moreover, we detect nebular emission in one dE with a gas velocity offset suggesting ongoing gas stripping in Virgo. We suggest that the low-$\lambda_{R}$ dEs in our sample were processed by their previous host halo, prior to their infall to Virgo, and that the high-$\lambda_{R}$ dEs may be experiencing ram pressure stripping in Virgo.