Evidence of Absence of Tidal Features in the Outskirts of Ultra Diffuse Galaxies in the Coma Cluster

TL;DR

This study uses deep imaging and stacking techniques to investigate tidal features in ultra diffuse galaxies in the Coma cluster, finding no evidence of tidal disruption and suggesting high dark matter content.

Contribution

It provides the first systematic analysis of tidal features in UDGs in the Coma cluster using stacking, revealing their stability and high dark matter fraction.

Findings

No evidence of tidal disruption up to 4 effective radii.

Average tidal radius >7 kpc for Coma UDGs.

Dark matter fraction within tidal radius >99%.

Abstract

We study the presence of tidal features associated with ultra diffuse galaxies (UDGs) in galaxy clusters. Specifically, we stack deep Subaru images of UDGs in the Coma cluster to determine whether they show position angle twists at large radii. Selecting galaxies with central surface brightness (g-band) >24 magarcsec^{-2} and projected half-light radius >1.5 kpc, we identify 287 UDGs in the Yagi et al. 2016 catalog of low surface brightness Coma objects. The UDGs have apparent spheroidal shapes with median Sersic index ~ 0.8 and median axis-ratio ~ 0.7. The images are processed by masking all background objects and rotating to align the major axis before stacking them in bins of properties such as axis ratio, angle of major axis with respect to the cluster center and separation from cluster center. Our image stacks reach further than 7 kpc (~4r_e). Analysis of the isophotes of the stacks reveal that the ellipticity remains constant up to the last measured point, which means that the individual galaxies have a non-varying position angle and axis ratio and show no evidence for tidal disruption out to ~ 4r_e. We demonstrate this explicitly by comparing our stacks with stacks of model UDGs with and without tidal features in their outskirts. We infer that the average tidal radius of the Coma UDGs is >7 kpc and estimate that the average dark matter fraction within the tidal radius of the UDGs inhabiting the innermost 0.5 Mpc of Coma is > 99%.