Elemental Abundances in M31: The Kinematics and Chemical Evolution of Dwarf Spheroidal Satellite Galaxies

Creators: Kirby, Evan N.; Gilbert, Karoline M.; Escala, Ivanna; Wojno, Jennifer; Guhathakurta, Puragra; Majewski, Steven R.; Beaton, Rachael L.

Abstract

We present deep spectroscopy from Keck/DEIMOS of Andromeda I, III, V, VII, and X, all of which are dwarf spheroidal satellites of M31. The sample includes 256 spectroscopic members across all five dSphs. We confirm previous measurements of the velocity dispersions and dynamical masses, and we provide upper limits on bulk rotation. Our measurements confirm that M31 satellites obey the same relation between stellar mass and stellar metallicity as Milky Way (MW) satellites and other dwarf galaxies in the Local Group. The metallicity distributions show trends with stellar mass that are similar to those of MW satellites, including evidence in massive satellites for external influence, like pre-enrichment or gas accretion. We present the first measurements of individual element ratios, like [Si/Fe], in the M31 system, as well as measurements of the average [α/Fe] ratio. The trends of [α/Fe] with [Fe/H] also follow the same galaxy mass–dependent patterns as MW satellites. Less massive galaxies have more steeply declining slopes of [α/Fe] that begin at lower [Fe/H]. Finally, we compare the chemical evolution of M31 satellites to M31's Giant Stellar Stream and smooth halo. The properties of the M31 system support the theoretical prediction that the inner halo is composed primarily of massive galaxies that were accreted early. As a result, the inner halo exhibits higher [Fe/H] and [α/Fe] than surviving satellite galaxies.

Additional Information

© 2020 The American Astronomical Society. Received 2019 August 29; revised 2019 December 1; accepted 2019 December 3; published 2020 January. We are grateful to Luis Vargas for providing a data table of M31 dSph measurements, including effective temperature. We thank Brent Belland for helpful discussion on the rotation model and Alexander Ji for insightful conversation. This material is based upon work supported by the National Science Foundation under grant Nos. AST-1614081 and AST-1614569. E.N.K. gratefully acknowledges support from a Cottrell Scholar award administered by the Research Corporation for Science Advancement, as well as funding from generous donors to the California Institute of Technology. I.E. acknowledges support from a National Science Foundation (NSF) Graduate Research Fellowship under grant No. DGE-1745301. P.G., S.R.M., and R.L.B. acknowledge prior funding from collaborative NSF grants AST-0307842, AST-0307851, AST-0607726, AST-0807945, AST-1009882, AST-1009973, and AST-1010039. Support for this work was provided by NASA through Hubble Fellowship grant #51386.01 awarded to R.L.B. by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. We are grateful to the many people who have worked to make the Keck Telescope and its instruments a reality, as well as to operate and maintain the Keck Observatory. The authors wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented herein would have been possible. We also express our deep gratitude to the staff at academic and telescope facilities whose labor maintains spaces for scientific inquiry. Facility: Keck:II (DEIMOS). - Software: spec2d (Cooper et al. 2012; Newman et al. 2013), MOOG (Sneden 1973; Sneden et al. 2012), ATLAS9 (Kurucz 1993), MPFIT (Markwardt 2012).

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