New Velocity Measurements of NGC 5128 Globular Clusters out to 130 kpc: Outer Halo Kinematics, Substructure and Dynamics

TL;DR

This study provides extensive new velocity data for globular clusters around NGC 5128, revealing outer halo substructures, kinematic behaviors, and an estimate of the galaxy's total mass, advancing understanding of galaxy assembly.

Contribution

It presents the first large-scale velocity measurements of GCs out to 130 kpc in NGC 5128, identifying halo substructures and analyzing their kinematics and implications for galaxy mass.

Findings

Extended GC velocity measurements to 130 kpc.

Detection of halo substructures associated with stellar streams.

Estimated galaxy mass of approximately 2.5 trillion solar masses.

Abstract

We present new radial velocity measurements from the Magellan and the Anglo-Australian Telescopes for 174 previously known and 122 newly confirmed globular clusters (GCs) around NGC 5128, the nearest accessible massive early-type galaxy at D=3.8 Mpc. Remarkably, 28 of these newly confirmed GCs are at projected radii >50' ($\gtrsim 54$ kpc), extending to $\sim 130$ kpc, in the outer halo where few GCs had been confirmed in previous work. We identify several subsets of GCs that spatially trace halo substructures that are visible in red giant branch star maps of the galaxy. In some cases, these subsets of GCs are kinematically cold, and may be directly associated with and originate from these specific stellar substructures. From a combined kinematic sample of 645 GCs, we see evidence for coherent rotation at all radii, with a higher rotation amplitude for the metal-rich GC subpopulation. Using the tracer mass estimator, we measure a total enclosed mass of $2.5\pm0.3 \times 10^{12} M_{\odot}$ within $\sim 120$ kpc, an estimate that will be sharpened with forthcoming dynamical modeling. The combined power of stellar mapping and GC kinematics makes NGC 5128 an ongoing keystone for understanding galaxy assembly at mass scales inaccessible in the Local Group.