The star formation history of the first bulge fossil fragment candidate Terzan 5

TL;DR

This study reconstructs the star formation history of Terzan 5, revealing a prolonged, multi-episode star formation process that supports its classification as a fossil of ancient massive star-forming clumps in the Milky Way bulge.

Contribution

It provides the first detailed star formation history of Terzan 5, confirming its multi-episode formation and supporting its role as a bulge fossil fragment.

Findings

70% of stars formed 12-13 Gyr ago

Detected multiple star formation episodes

Supports self-enrichment in primordial clumps

Abstract

Context. Terzan 5 and Liller 1 are the only bulge stellar clusters hosting multi-iron and multi-age stellar populations. They are therefore claimed to constitute a novel class of astrophysical objects: the fossils of massive star-forming clumps that possibly sank to the center of the Milky Way and contributed to the formation of the bulge. This is based on the hypothesis that the ancient clumps were able to retain iron-enriched supernova ejecta, later giving rise to younger and more metal-rich populations. Aims. A way to investigate this scenario is reconstructing their star formation histories (SFHs) and proving a prolonged and multi-episode star formation activity. Methods. Leveraging ground- and space-based high-resolution images, we derived the SFH of Terzan 5 by employing the color-magnitude diagram fitting routine SFERA. Results. The best-fit solution predicts an old, main peak occurred between 12 and 13 Gyr ago that generated 70 % of the current stellar mass, followed by a lower-rate star formation activity with two main additional bursts. Conclusions. These results indicate that Terzan 5, similarly to Liller 1, experienced a prolonged, multiepisode star formation activity, fueled by metal-enriched gas deposited in its central regions, in agreement with the expectations of a self-enrichment scenario in a primordial massive clump.