Clues to the formation of Liller 1 from modeling its complex star formation history

Abstract

Liller 1 and Terzan 5 are two massive systems in the Milky-Way bulge hosting populations characterized by significantly different ages ($\Delta t>7-8$ Gyr) and metallicities ($\Delta$[Fe/H]$\sim 1$ dex). Their origin is still strongly debated in the literature and all formation scenarios proposed so far require some level of fine-tuning. The detailed star formation histories (SFHs) of these systems may represent an important piece of information to assess their origin. Here we present the first attempt to perform such an analysis for Liller 1. The first key result we find is that Liller 1 has been forming stars over its entire lifetime. More specifically, three broad SF episodes are clearly detected: 1) a dominant one, occurred some 12-13 Gyr ago with a tail extending for up to $\sim 3$ Gyr, 2) an intermediate burst, between 6 and 9 Gyr ago, 3) and a recent one, occurred between 1 and 3 Gyr ago. The old population contributes to about $70\%$ of the total stellar mass and the remaining fraction is almost equally split between the intermediate and young populations. If we take these results at a face value, they would suggest that this system unlikely formed through the merger between an old globular cluster and a Giant Molecular Cloud, as recently proposed. On the contrary, our findings provide further support to the idea that Liller 1 is the surviving relic of a massive primordial structure that contributed to the Galactic bulge formation, similarly to the giant clumps observed in star-forming high-redshift galaxies.

23 pages, 14 figures; accepted for publication in ApJ

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Cited by in corpus (13)

• First evidence of multi-iron sub-populations in the Bulge Fossil Fragment candidate Liller 1
• Modeling the chemical enrichment history of the Bulge Fossil Fragment Terzan 5
• Internal kinematics and structure of the bulge globular cluster NGC 6569
• The Bulge Cluster Origin (BulCO) survey at the ESO-VLT: probing the early history of the Milky Way assembling. Design and first results in Liller1
• The $Hubble$ Missing Globular Cluster Survey. I. Survey overview and the first precise age estimate for ESO452-11 and 2MASS-GC01
• A Photometric in-depth look at the core-collapsed globular cluster NGC 6284
• On the manifest link between Terzan 5 and the Galactic bulge
• The bulge globular cluster Terzan 6 as seen from multi-conjugate adaptive optics and HST
• Extended Main-Sequence Turnoff and Red Clump in intermediate-age star clusters: A study of NGC 419
• Bulge Fossil Fragments as a new population of factories of gravitational wave sources in the Galaxy
• The multi-age stellar populations of Terzan 5 as revealed by JWST
• Revealing the stellar population of the ultra-obscured Galactic globular cluster Glimpse-C02
• A candidate to the long sought optical counterpart to the Rapid Burster in the bulge fossil fragment Liller 1