A 3D view of the Hydra I galaxy cluster core - I. Kinematic substructures

TL;DR

This study reveals complex, asymmetric kinematic substructures in the Hydra I galaxy cluster core, indicating a dynamically young stellar halo influenced by ongoing interactions and disruptions.

Contribution

It introduces a novel method using FORS2 in MXU mode to map 3D kinematics, uncovering detailed substructures in the Hydra I cluster core.

Findings

Velocity dispersion varies with radius and azimuth.

Kinematic irregularities align with tidal features.

The stellar halo is dynamically young and disrupted.

Abstract

We used FORS2 in MXU mode to mimic a coarse 'IFU' in order to measure the 3D large-scale kinematics around the central Hydra I cluster galaxy NGC 3311. Our data show that the velocity dispersion field varies as a function of radius and azimuthal angle and violates point symmetry. Also, the velocity field shows similar dependence, hence the stellar halo of NGC 3311 is a dynamically young structure. The kinematic irregularities coincide in position with a displaced diffuse halo North-East of NGC 3311 and with tidal features of a group of disrupting dwarf galaxies. This suggests that the superposition of different velocity components is responsible for the kinematic substructure in the Hydra I cluster core.