The globular cluster AM 4: yet another young globular associated with the Sgr Dwarf Spheroidal galaxy?

TL;DR

This study provides new photometric data and analysis of globular cluster AM 4, suggesting it is a young, metal-poor cluster possibly associated with the Sagittarius dwarf galaxy, and highlights its ongoing tidal disruption.

Contribution

It offers the first detailed photometric analysis of AM 4, estimating its age, metallicity, and potential association with Sgr dSph, and discusses its tidal disruption status.

Findings

AM 4 is a young (~9 Gyr) and metal-poor ([Fe/H]=-0.97) globular cluster.

It is undergoing strong tidal stress and is close to dissolution.

Its position and distance are compatible with association to the Sgr dSph stream.

Abstract

The complete census of globular clusters formerly belonging to the Sgr dSph and now deposited into the Galactic halo is an important contribution to our comprehension of the evolution and disruption of this dwarf galaxy. We investigate in this study the possibility that the poorly known "old" globular AM 4 might be associated with the Sagittarius dwarf galaxy, and at the same time provide more solid estimate of its basic parameters. New high quality BVI photometry is presented, from which an improved Color Ma gnitude Diagram is constructed, and estimates of age and distance are then derived. The distance and Galactic position are finally investigated in details. AM~4 is found to be a low luminosity (M$_V$=-1.82) cluster undergoing strong tidal stress by the Milky Way and on the verge to be dissolved. Besides, and at odds with previous suggestions, we provide evidences that AM 4 is indeed young, with an age around 9 Gyrs (as Terzan~7), but somewhat more metal poor ([Fe/H=-0.97]). AM~4 is located at 33$_{-4}^{+3}$ kpc from the Sun, in a direction and at distance not totally incompatible with the Sgr dSph stream. Although we significantly improved our knowledge of AM 4, further studies are encouraged to obtain radial velocity and metallicity to d emonstrate more firmly (or deny) the association to Sgr