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

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.

APOGEE Detection of N-rich stars in the tidal tails of Palomar 5

“…It is important to note that tidal or Jacobi radii are notoriously uncertain, being subject to systematic errors related to their method of determination and the input parameters adopted. Thus, the more recent data from Gaia eDR3 provide a much greater value for the tidal radius than that which was used by Fernández-Trincado et al (2021b) which, considering the propagation of uncertainties of input parameters, would place the extra-tidal N-rich star discovered within 1𝜎 of the Jacobi radius of 37 arcminutes determined by . 3 We will present a discussion of tidal radius uncertainties in Schiavon et al (2021, in prep.…”

“…Interestingly, Fernández-Trincado et al (2021b) identified the presence of N-rich candidates several tidal radii away from M 54, a globular cluster in the core of the Sagittarius dSph (see Bellazzini et al 2008, for an in depth discussion of M54 in the context of galaxy nucleation.) The discovery by Fernández-Trincado et al (2021b) suggests that the process of field pollution by so-called "second-generation" cluster stars is taking place in the core of a dwarf galaxy undergoing tidal disruption during its merger with the Milky Way. It is important to note that tidal or Jacobi radii are notoriously uncertain, being subject to systematic errors related to their method of determination and the input parameters adopted.…”

On the formation of globular clusters: comparison with observations

“…Mucciarelli et al 2007;Niederhofer et al 2017), in GCs located in other local dwarf galaxies (e.g. Larsen et al 2014;Sills et al 2019;Fernández-Trincado et al 2021) and in the GCs of M31 (Schiavon et al 2013).…”

Galactic ArchaeoLogIcaL ExcavatiOns (GALILEO) I. An updated census of APOGEE N-rich giants across the Milky Way

“…Some of these now defunct dwarf galaxies have been identified as stellar structures or debris that populate the present-day Galactic field (e.g., the bulge, disk, and/or halo of the MW), and they are very phase mixed. Among the most populated progenitors associated to these systems are Sagittarius dwarf spheroidal galaxy (Ibata et al 1994;Hasselquist et al 2017Hasselquist et al , 2019 and its dispersed streams (Hasselquist et al 2017(Hasselquist et al , 2019, which also preserve traces of tidal stripping and disruption of globular clusters (GCs) (see e.g., Fernández-Trincado et al 2021c), followed by the unusual Omega Centauri (NGC 5139) system (Villanova et al 2014), together with its hypothesized "Fimbulthul" stream (Ibata et al 2019) as well as its controversial tidal tails and stellar debris (Da Costa & Coleman 2008;Majewski et al 2012;Fernández-Trincado et al 2015a,b;Marconi et al 2014;Sollima 2020), and a number of stellar streams with variate origins and over a wide range of metallicities (Wan et al 2020;Ibata et al 2021;Martin et al 2022). These claims are bolstered by the detection of extratidal stars with unusual GC-like abundance patterns, similar to that seen toward the Large and Small Magellanic systems today (Fernández-Trincado et al 2020b), the stellar halo (Hanke et al 2020), and the Galactic bulge (Minniti et al 2018;Fernández-Trincado et al 2021b).…”