Threshing in Action - The tidal disruption of a dwarf galaxy by the Hydra I Cluster

TL;DR

This paper reports the discovery of tidal disruption features in a dwarf galaxy within the Hydra I cluster, supported by observations and N-body simulations, revealing insights into galaxy disruption processes in cluster environments.

Contribution

The study provides the first detailed analysis of a dwarf galaxy undergoing tidal disruption in a galaxy cluster, combining observational evidence with simulations to understand its dynamics.

Findings

HCC-087 shows S-shaped morphology indicative of tidal disruption.

HCC-087 is likely at its first apocenter, about 150 kpc from the cluster center.

Tidal tails are oriented perpendicular to the orbit, characteristic of disruption processes.

Abstract

We report on the discovery of strong tidal features around a dwarf spheroidal galaxy in the Hydra I galaxy cluster, indicating its ongoing tidal disruption. This very low surface brightness object, HCC-087, was originally classified as an early-type dwarf in the Hydra Cluster Catalogue (HCC), but our re-analysis of the ESO-VLT/FORS images of the HCC unearthed a clear indication of an S-shaped morphology and a large spatial extent. Its shape, luminosity (M_V=-11.6 mag), and physical size (at a half-light radius of 3.1 kpc and a full length of ~5.9 kpc) are comparable to the recently discovered NGC 4449B and the Sagittarius dwarf spheroidal, all of which are undergoing clear tidal disruption. Aided by N-body simulations we argue that HCC-087 is currently at its first apocenter, at 150 kpc, around the cluster center and that it is being tidally disrupted by the galaxy cluster's potential itself. An interaction with the near-by (50 kpc) S0 cluster galaxy HCC-005, at M* ~ 3 x 10^10 M_sun is rather unlikely, as this constellation requires a significant amount of dynamical friction and thus low relative velocities. The S-shaped morphology and large spatial extent of the satellite would, however, also appear if HCC-087 would orbit the cluster center. These features appear to be characteristic properties of satellites that are seen in the process of being tidally disrupted, independent of the environment of the destruction. An important finding of our simulations is an orientation of the tidal tails perpendicular to the orbit.