The dual nature of the tidal tails of NGC 5904 (M5)

TL;DR

This study investigates the dual metallicity and kinematic properties of M5's tidal tails, revealing evidence for a complex formation history involving possible cluster collision and different dark matter subhalo scenarios.

Contribution

It uncovers the dual metallicity regimes in M5's tidal tails and links their kinematic properties to different dark matter subhalo formation scenarios or in-situ origins.

Findings

Metal-rich tail stars match cuspy subhalo velocity dispersion predictions.

Metal-poor tail stars align with cored subhalo or in-situ formation scenarios.

Evidence suggests M5 collided with another cluster, influencing tail composition.

Abstract

The tangential velocity dispersion of stars belonging to the Milky Way globular cluster's tidal tails has recently been found from N-body simulations to be a parameter that distinguishes between cored and cuspy profiles of low-mass dwarf galaxy dark matter subhaloes where that globular cluster formed, and the in-situ formation scenario. In this context, we discovered that M5's tidal tails are composed by stars at two different metallicity regimes ([Fe/H] ~ -1.4 dex and -2.0 dex). The more metal-rich tidal tail stars are of the same metal content than M5's members and have a tangential velocity dispersion that coincides with the predicted value for a cuspy formation scenario (subhalo mass $\sim$ 10$^9$ M$_{\odot}$). The more metal-poor stars, that are found along the entire M5 tidal tails and have similar distributions to their more metal-rich counterparts in the M5 colour-magnitude diagram and orbit trajectory, have a tangential velocity dispersion that refers to a cored subhalo (mass $\sim$ 10$^9$ M$_{\odot}$) or an in-situ formation scenario. In order to reconcile the dual distribution of M5 tidal tail stars, in kinematics and chemistry, we propose that M5 collided with another more metal-poor and less massive globular cluster anytime before or after it was accreted into the Milky Way.