Metallicity and α-Element Abundance Gradients along the Sagittarius Stream as Seen by APOGEE

Christian R. Hayes, Steven R. Majewski, Sten Hasselquist, Borja Anguiano, Matthew Shetrone, David R. Law, Ricardo P. Schiavon, Katia Cunha, Verne V. Smith, Rachael L. Beaton, Adrian M. Price-Whelan, Carlos Allende Prieto, Giuseppina Battaglia, Dmitry Bizyaev, Joel R. Brownstein, Roger E. Cohen, Peter M. Frinchaboy, D. A. García-Hernández, Ivan Lacerna, Richard R. LaneSzabolcs Mészáros, Christian Moni Bidin, Ricardo R. Mũnoz, David L. Nidever, Audrey Oravetz, Daniel Oravetz, Kaike Pan, Alexandre Roman-Lopes, Jennifer Sobeck, Guy Stringfellow

Research output: Contribution to journalArticlepeer-review

29 Scopus citations

Abstract

Using 3D positions and kinematics of stars relative to the Sagittarius (Sgr) orbital plane and angular momentum, we identify 166 Sgr stream members observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) that also have Gaia DR2 astrometry. This sample of 63/103 stars in the Sgr trailing/leading arm is combined with an APOGEE sample of 710 members of the Sgr dwarf spheroidal core (385 of them newly presented here) to establish differences of 0.6 dex in median metallicity and 0.1 dex in [α/Fe] between our Sgr core and dynamically older stream samples. Mild chemical gradients are found internally along each arm, but these steepen when anchored by core stars. With a model of Sgr tidal disruption providing estimated dynamical ages (i.e., stripping times) for each stream star, we find a mean metallicity gradient of 0.12 ± 0.03 dex Gyr-1 for stars stripped from Sgr over time. For the first time, an [α/Fe] gradient is also measured within the stream, at 0.02 ± 0.01 dex Gyr-1 using magnesium abundances and at 0.04 ± 0.01 dex Gyr-1 using silicon, which imply that the Sgr progenitor had significant radial abundance gradients. We discuss the magnitude of those inferred gradients and their implication for the nature of the Sgr progenitor within the context of the current family of Milky Way satellite galaxies, and we suggest that more sophisticated Sgr models are needed to properly interpret the growing chemodynamical detail we have on the Sgr system.

Original languageEnglish (US)
Article number63
JournalAstrophysical Journal
Volume889
Issue number1
DOIs
StatePublished - Jan 20 2020
Externally publishedYes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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