A comparative analysis of the chemical compositions of Gaia-Enceladus/Sausage and Milky Way satellites using APOGEE

Abstract

We use data from the 17th data release of the Apache Point Observatory Galactic Evolution Experiment (APOGEE 2) to contrast the chemical composition of the recently discovered Gaia Enceladus/Sausage system (GE/S) to those of ten Milky Way (MW) dwarf satellite galaxies: LMC, SMC, Boötes I, Carina, Draco, Fornax, Sagittarius, Sculptor, Sextans and Ursa Minor. Our main focus is on the distributions of the stellar populations of those systems in the [Mg/Fe]-[Fe/H] and [Mg/Mn]-[Al/Fe] planes, which are commonly employed in the literature for chemical diagnosis and where dwarf galaxies can be distinguished from in situ populations. We show that, unlike MW satellites, a GE/S sample defined purely on the basis of orbital parameters falls almost entirely within the locus of ‘accreted’ stellar populations in chemical space, which is likely caused by an early quenching of star formation in GE/S. Due to a more protracted history of star formation, stars in the metal-rich end of the MW satellite populations are characterized by lower [Mg/Mn] than those of their GE/S counterparts. The chemical compositions of GE/S stars are consistent with a higher early star formation rate than MW satellites of comparable and even higher mass, suggesting that star formation in the early universe was strongly influenced by other parameters in addition to mass. We find that the direction of the metallicity gradient in the [Mg/Mn]–[Al/Fe] plane of dwarf galaxies is an indicator of the early star formation rate of the system.

The Metal-weak Milky Way Stellar Disk Hidden in the Gaia–Sausage–Enceladus Debris: The APOGEE DR17 View

“…This is further supported by the models from Horta et al (2021) and Fernandes et al (2023) that show that a lighter system will reach a maximum [Al/Fe] value that is smaller than the main body of the Milky Way disk. See also Fernandes et al (2023) for a full characterization of low-mass systems in APOGEE.…”

“…The smaller systems all have [Al/Fe] systematically lower than the Milky Way disk, indicating that it is not unreasonable to assume that stars from a system that has formed in relative isolation and then accretes onto the main body of the Milky Way will be possible to identify thanks to their low [Al/Fe]. This is further supported by the models from Horta et al (2021) and Fernandes et al (2023) that show that a lighter system will reach a maximum [Al/Fe] value that is smaller than the main body of the Milky Way disk. See also Fernandes et al (2023) for a full characterization of low-mass systems in APOGEE.…”

“…Initial attempts to understand this plane using chemical evolution models have found a difference in the expected distribution of low-mass Gaia-Sausage-Enceladus-like galaxies, present-day dwarf galaxies, and Milky Way-like galaxies. Horta et al (2021) and Fernandes et al (2023) provide chemical evolution models in the Mg-Mn-Al-Fe plane for these different types of galaxies.…”

Imprints of Sagittarius accretion event: Young O-rich stars and discontinuous chemical evolution in Milky Way disc

“…Although Sgr is not the only satellite of the Milky Way that might be affecting our Galaxy presently, it exhibits the closest resemblance in chemical signature to the infalling gas responsible for the observed deficiencies in magnesium abundance. A comparative analysis [38] of the chemical compositions of various Milky Way dwarf satellite galaxies, based on APOGEE data [29,30], has shown that among the ten known Milky Way dwarf satellites, Sgr stands out as the only satellite possessing near-solar metallicity ([Fe/H] ∼−0.1) and a deficit in [Mg/Fe] ∼−0.2. In contrast, another satellite within a similar metallicity range, the Large Magellanic Cloud (LMC), does not exhibit a distinct depletion in [Mg/Fe], with [Mg/Fe] ∼−0.05 at the metal-rich end [38].…”

Abundance Analysis of Stars at Large Radius in the Sextans Dwarf Spheroidal Galaxy*

“…Previous studies have derived detailed chemical abundances of stars in Sextans using high-resolution spectroscopy (Shetrone et al 2001;Aoki et al 2009;Tafelmeyer et al 2010;Honda et al 2011;Aoki et al 2020;Lucchesi et al 2020;Theler et al 2020;Mashonkina et al 2022;Fernandes et al 2023). These studies have been limited to stars near the center of Sextans, within the inner » ¢ 40 or so.…”