Assessing the chemical DNA of Liller1: a spectroscopic insight of the Galactic Bulge formation

In agreement with the chain and clumpy galaxies observations (e.g., Genzel et al. 2011), bulges of spiral galaxies form through mergers of massive clumps caused by disk instability and fragmentation (e.g., Immeli et al. 2004). While most of these clumps are predicted to dissolve and form the bulge, a few of them may have survived and appear as globular clusters (Bournaud 2016). These ”Bulge Fossil Fragments” (BFFs) host multi-iron and multi-age sub-populations, with the same ”chemical DNA” of the bulge. Indeed, specific abundance patterns (e.g. [α/Fe] vs [Fe/H]) trace the ISM enrichment process, providing pure “chemical DNA tests”. Thus, studying the Galactic Bulge is crucial to probe the early history of the Milky Way, being the only spheroid where kinematic, photometric and chemical properties of individual stars can be explored. In this work I present the chemical screening of a sample of 10 stars in the GC-like stellar system Liller1, one of the candidate BFFs discovered so far (Ferraro et al. 2021). The data have been acquired with the NIR echelle spectrograph CRIRES+ at the VLT through the ongoing Large Programme P110.24A4 (PI: Ferraro). This project is part of the Bulge Cluster Origin (BulCO) survey, which aims at performing the same chemical analysis on a large sample of representative Bulge stellar systems. The high resolution of these spectra (R=50,000) makes them ideal for the safe identification and measurement of the atomic and molecular spectral lines of the most powerful chemical DNA indicators. The chemical analysis of the spectra (obtained in the H and K-band) performed with the well-tested spectral synthesis technique allowed the measure of the abundances of key elements, like iron, calcium, silicon and magnesium. Despite the limited sample size, this study has confirmed the presence of multiple iron populations within Liller 1, thus solidly constraining its nature spectroscopically and advancing our understanding of this intriguing object.