APOGEE spectroscopic evidence for chemical anomalies in dwarf galaxies: The case of M 54 and Sagittarius

¹ Instituto de Astronomía y Ciencias Planetarias, Universidad de Atacama, Copayapu 485, Copiapó, Chile
e-mail: jose.fernandez@uda.cl, jfernandezt87@gmail.com
² Institut Utinam, CNRS UMR 6213, Université Bourgogne-Franche-Comté, OSU THETA Franche-Comté, Observatoire de Besançon, BP 1615, 25010 Besançon Cedex, France
³ Centro de Investigación en Astronomía, Universidad Bernardo O Higgins, Avenida Viel 1497, Santiago, Chile
⁴ Department of Physics and JINA Center for the Evolution of the Elements, University of Notre Dame, Notre Dame, IN 46556, USA
⁵ Depto. de Cs. Físicas, Facultad de Ciencias Exactas, Universidad Andrés Bello, Av. Fernández Concha 700, Las Condes, Santiago, Chile
⁶ Vatican Observatory, 00120 Vatican City State, Italy
⁷ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile
⁸ Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
⁹ Departamento de Astronomía, Casilla 160-C, Universidad de Concepción, Concepción, Chile
¹⁰ Departamento de Astronomía, Universidad de La Serena, 1700000 La Serena, Chile
¹¹ Instituto de Investigación Multidisciplinario en Ciencia y Tecnología, Universidad de La Serena, Benavente 980, La Serena, Chile
¹² Apache Point Observatory and New Mexico State University, Sunspot, NM 88349, USA
¹³ Sternberg Astronomical Institute, Moscow State University, Moscow, Russia

Received: 9 January 2021
Accepted: 8 February 2021

Abstract

We present evidence for globular cluster stellar debris in a dwarf galaxy system (Sagittarius; Sgr) based on an analysis of high-resolution H-band spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We add [N/Fe], [Ti/Fe], and [Ni/Fe] abundance ratios to the existing sample of potential members of M 54; this is the first time that [N/Fe] abundances are derived for a large number of stars in M 54. Our study reveals the existence of a significant population of nitrogen- (with a large spread, ≳1 dex) and aluminum-enriched stars with moderate Mg depletions in the core of the M 54+Sgr system, which share the light element anomalies characteristic of second-generation globular cluster stars (GC), thus tracing the typical phenomenon of multiple stellar populations seen in other Galactic GCs at similar metallicity, confirming earlier results based on the Na-O anti-correlation. We further show that most of the stars in M 54 exhibit different chemical patterns evidently not present in Sgr field stars. Furthermore, we report the serendipitous discovery of a nitrogen-enhanced extra-tidal star that has GC second-generation-like chemical patterns for which both chemical and kinematic evidence are commensurate with the hypothesis that the star has been ejected from M 54. Our findings support the existence of chemical anomalies associated with likely tidally shredded GCs that are in dwarf galaxies in the Local Group. These findings motivate future searches for such bona fide stars along other known Milky Way streams.