Is Liller 1 a building block of the Galactic bulge? -- Evidence with APOGEE

Anna Liptrott; Ricardo P. Schiavon; Andrew C. Mason; Sebastian Kamann; Borja Anguiano; Roger E. Cohen; José G. Fernández-Trincado; Danny Horta; Steven R. Majewski; Dante Minniti; David M. Nataf; Michael J. W. O'Connor; Dominic Wearne

arXiv · 2510.07411

Is Liller 1 a building block of the Galactic bulge? -- Evidence with APOGEE

Anna Liptrott·Ricardo P. Schiavon·Andrew C. Mason·Sebastian Kamann·Borja Anguiano·Roger E. Cohen·José G. Fernández-Trincado·Danny Horta·Steven R. Majewski·Dante Minniti·David M. Nataf·Michael J. W. O'Connor·Dominic Wearne

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Abstract

Liller 1 is a stellar system orbiting within the inner 0.8kpc of the Galactic centre, characterised by a wide spread in age and metallicity, indicating a high mass. Liller 1 has been proposed to be a major contributor to the stellar mass of the Galactic bulge, yet its origin is subject to debate. We employ Sloan Digital Sky Survey IV (SDSS-IV) data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) to test scenarios proposed to explain the nature of Liller 1. Using a random sampling technique, we contrast the chemical compositions of Liller 1 stellar members with those of the bulge, inner disc, outer disk and solar neighbourhood. The chemistry of Liller 1 deviates from that of the bulge population at the 2-3$\sigma$ level for $\alpha$-elements Mg, Si, and Ca. We conclude that the progenitor of Liller 1 was not a major contributor of stellar mass to the bulge. Furthermore, we find the abundance pattern of Liller 1 to deviate at the 2$\sigma$ level from that of inner disk stars, ruling out the cluster rejuvenation scenario. Finally, we find that Liller 1 is chemically distinct from solar and outer disc populations, suggesting that the progenitor of Liller 1 is unlikely to be an in-situ massive clump formed at high redshift, from disc gravitational instabilities, that migrated inwards and coalesced with others into the bulge. Finally, we suggest that Liller 1 is a minor contributor to the stellar mass of the inner Galaxy, possibly of extragalactic origin.

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Anna Liptrott, Ricardo P. Schiavon, Andrew C. Mason, Sebastian Kamann, Borja Anguiano, Roger E. Cohen, José G. Fernández-Trincado, Danny Horta, Steven R. Majewski, Dante Minniti, David M. Nataf, Michael J. W. O'Connor, Dominic Wearne. 2025-10-08. Is Liller 1 a building block of the Galactic bulge? -- Evidence with APOGEE. https://arxiv.org/abs/2510.07411

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