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Elemental Abundances in M31: [Fe/H] and [α/Fe] in M31 Dwarf Galaxies Using Coadded Spectra

Wojno, Jennifer and Gilbert, Karoline M. and Kirby, Evan N. and Escala, Ivanna and Beaton, Rachael L. and Tollerud, Erik J. and Majewski, Steven R. and Guhathakurta, Puragra (2020) Elemental Abundances in M31: [Fe/H] and [α/Fe] in M31 Dwarf Galaxies Using Coadded Spectra. Astrophysical Journal, 895 (2). Art. No. 78. ISSN 1538-4357.

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We present chemical abundances of red giant branch (RGB) stars in the dwarf spheroidal (dSph) satellite system of Andromeda (M31), using spectral synthesis of medium-resolution (R ~ 6000) spectra obtained with the Keck II telescope and Deep Imaging Multi-Object Spectrometer spectrograph via the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo survey. We coadd stars according to their similarity in photometric metallicity or effective temperature to obtain a signal-to-noise ratio (S/N) high enough to measure average [Fe/H] and [α/Fe] abundances. We validate our method using high S/N spectra of RGB stars in Milky Way globular clusters, as well as deep observations for a subset of the M31 dSphs in our sample. For this set of validation coadds, we compare the weighted average abundance of the individual stars with the abundance determined from the coadd. We present individual and coadded measurements of [Fe/H] and [α/Fe] for stars in 10 M31 dSphs, including the first [α/Fe] measurements for And IX, XIV, XV, and XVIII. These fainter, less massive dSphs show declining [α/Fe] relative to [Fe/H], implying an extended star formation history (SFH). In addition, these dSphs also follow the same mass–metallicity relation found in other Local Group satellites. The conclusions we infer from coadded spectra agree with those from previous measurements in brighter M31 dSphs with individual abundance measurements, as well as conclusions from photometric studies. These abundances greatly increase the number of spectroscopic measurements of the chemical composition of M31's less massive dwarf satellites, which are crucial to understanding their SFH and interaction with the M31 system.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Wojno, Jennifer0000-0002-3233-3032
Gilbert, Karoline M.0000-0003-0394-8377
Kirby, Evan N.0000-0001-6196-5162
Escala, Ivanna0000-0002-9933-9551
Beaton, Rachael L.0000-0002-1691-8217
Tollerud, Erik J.0000-0002-9599-310X
Majewski, Steven R.0000-0003-2025-3147
Guhathakurta, Puragra0000-0001-8867-4234
Additional Information:© 2020 The American Astronomical Society. Received 2019 November 30; revised 2020 April 20; accepted 2020 April 21; published 2020 May 28. We thank the anonymous referee for thorough comments and suggestions, which have greatly improved the quality of the manuscript. This material is based upon work supported by the National Science Foundation under grant Nos. AST-1614569 (J.W., K.M.G.) and AST-1614081 (E.N.K., I.E.). 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. R.L.B. and S.R.M. thank NSF grants AST-0307842, AST-0607726, AST-1009882, and AST-1413269. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013, 2018).11 Facility: Keck:II (DEIMOS). - Software: Astropy (Astropy Collaboration et al. 2013), Matplotlib (Hunter 2007), numpy (van der Walt et al. 2011), scipy (Virtanen et al. 2020), emcee (Foreman-Mackey et al. 2013).
Group:Astronomy Department
Funding AgencyGrant Number
Cottrell Scholar of Research CorporationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1745301
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:Andromeda Galaxy ; Chemical abundances
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Andromeda Galaxy (39); Chemical abundances (224); Dwarf galaxies (416)
Record Number:CaltechAUTHORS:20200528-105015601
Persistent URL:
Official Citation:Jennifer Wojno et al 2020 ApJ 895 78
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103518
Deposited By: Tony Diaz
Deposited On:28 May 2020 18:37
Last Modified:28 May 2020 18:37

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