A discrete chemo-dynamical model of M87's globular clusters: Kinematics extending to ~ 400 kpc

TL;DR

This study models the mass distribution and kinematics of M87's globular clusters extending to 430 kpc, revealing insights into dark matter content, galaxy dynamics, and globular cluster origins using discrete chemo-dynamical methods.

Contribution

It introduces a chemo-dynamical axisymmetric Jeans model for M87's globular clusters, extending kinematic analysis to large radii and comparing cusped versus cored dark matter halos.

Findings

Total mass within 400 kpc is approximately 2.16 x 10^{13} solar masses.

Dark matter fraction increases significantly when including stellar mass-to-light ratio gradients.

Red and blue globular clusters show distinct rotation and velocity anisotropy patterns.

Abstract

We study the mass distribution and kinematics of the giant elliptical galaxy M87 (NGC 4486) using discrete chemo-dynamical, axisymmetric Jeans equation modelling. Our catalogue comprises 894 globular clusters (GCs) extending to a projected radius of $\sim 430$ kpc with line-of-sight velocities and colours, and Multi Unit Spectroscopic Explorer (MUSE) integral field unit data within the central $2.4$ kpc of the main galaxy. The gravitational potential for our models is a combination of a luminous matter potential with a varying mass-to-light ratio for the main galaxy, a supermassive black hole and a dark matter (DM) potential with a cusped or cored DM halo. The best-fitting models with either a cusped or a cored DM halo show no significant differences and both are acceptable. We obtain a total mass of $(2.16 \pm 0.38) \times 10^{13} M_{\odot}$ within $\sim$ 400 kpc. By including the stellar mass-to-light ratio gradient, the DM fraction increases from $\sim$ 26 percent (with no gradient) to $\sim$ 73 percent within $1\,R_e^{\rm maj}$ (major axis of half-light isophote, 14.2 kpc), and from $\sim$ 84 percent to $\sim$ 94 percent within $5\,R_e^{\rm maj}$ (71.2 kpc). Red GCs have moderate rotation with $V_{\rm max}/\sigma \sim$ 0.4, and blue GCs have weak rotation with $V_{\rm max}/\sigma \sim$ 0.1. Red GCs have tangential velocity dispersion anisotropy, while blue GCs are consistent with being nearly isotropic. Our results suggest that red GCs are more likely to be born in-situ, while blue GCs are more likely to be accreted.