TERZAN 5: the remnant of a pristine fragment of the Galactic Bulge?

TL;DR

Terzan 5 is a complex stellar system in the Galactic bulge with multiple populations and metallicities, indicating it is a remnant of a primordial bulge fragment rather than a typical globular cluster.

Contribution

This study reveals the detailed chemical and population complexity of Terzan 5, suggesting it is a relic of the bulge formation process, unlike typical globular clusters.

Findings

Presence of two main stellar populations with distinct metallicities.

Detection of a third, more metal-poor population.

Chemical similarity with bulge stars indicating a possible bulge relic.

Abstract

Terzan 5 is a stellar system in the Galactic bulge commonly catalogued as a globular cluster. Through dedicated NIR photometry and spectroscopy we have discovered that it harbors two main stellar populations defining two distinct red clumps (RCs) in the colour-magnitude diagram, and displaying different iron content: [Fe/H] = -0.2 and [Fe/H]=+0.3 for the faint and the bright red clumps, respectively. In addition, a third minor population with significantly lower metallicity ([Fe/H]=-0.79) has been recently detected, thus enlarging the metallicity range covered by Terzan 5 to Delta[Fe/H] ~ 1 dex. This evidence demonstrates that, similarly to omega Centauri in the Galactic halo, Terzan 5 is not a genuine globular cluster, but a stellar system that experienced a much more complex star formation and chemical enrichment history. Moreover the striking chemical similarity with the bulge stars suggests that Terzan 5 could be the relic of one of the massive clumps that contributed through strong dynamical interactions with other similar sub-structures) to the formation of the Galactic bulge.