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Elemental Abundances in M31: Iron and Alpha Element Abundances in M31’s Outer Halo

Gilbert, Karoline M. and Wojno, Jennifer and Kirby, Evan N. and Escala, Ivanna and Beaton, Rachael L. and Guhathakurta, Puragra and Majewski, Steven R. (2020) Elemental Abundances in M31: Iron and Alpha Element Abundances in M31’s Outer Halo. Astronomical Journal, 160 (1). Art. No. 41. ISSN 1538-3881.

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We present [Fe/H] and [α/Fe] abundances, derived using spectral synthesis techniques, for stars in M31's outer stellar halo. The 21 [Fe/H] measurements and 7 [α/Fe] measurements are drawn from fields ranging from 43 to 165 kpc in projected distance from M31. We combine our measurements with existing literature measurements, and compare the resulting sample of 23 stars with [Fe/H] and 9 stars with [α/Fe] measurements in M31's outer halo with [α/Fe] and [Fe/H] measurements, also derived from spectral synthesis, in M31's inner stellar halo (r < 26 kpc) and dSph galaxies. The stars in M31's outer halo have [α/Fe] patterns that are consistent with the largest of M31's dSph satellites (And I and And VII). These abundances provide tentative evidence that the [α/Fe] abundances of stars in M31's outer halo are more similar to the abundances of Milky Way halo stars than to the abundances of stars in M31's inner halo. We also compare the spectral synthesis–based [Fe/H] measurements of stars in M31's halo with previous photometric [Fe/H] estimates, as a function of projected distance from M31. The spectral synthesis–based [Fe/H] measurements are consistent with a large-scale metallicity gradient previously observed in M31's stellar halo to projected distances as large as 100 kpc.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Gilbert, Karoline M.0000-0003-0394-8377
Wojno, Jennifer0000-0002-3233-3032
Kirby, Evan N.0000-0001-6196-5162
Escala, Ivanna0000-0002-9933-9551
Beaton, Rachael L.0000-0002-1691-8217
Guhathakurta, Puragra0000-0001-8867-4234
Majewski, Steven R.0000-0003-2025-3147
Additional Information:© 2020. The American Astronomical Society. Received 2020 January 21; revised 2020 May 1; accepted 2020 May 21; published 2020 June 25. The authors 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. We thank the anonymous referee, whose careful reading of the manuscript improved the clarity of the paper. Support for this work was provided by NSF grants AST-1614569 (K.M.G., J.W.), AST-1614081 (E.N.K., I.E.), AST-1847909 (E.N.K.), and AST-1909497 (S.R.M.). P.G. acknowledges support from NSF grants AST-1412648, AST-1010039, AST-0607852, and AST-0307966. S.R.M. and R.L.B. acknowledge support from NSF grants AST-1413269, AST-1009882, AST-0607726, and AST-0307842. 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. 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. The analysis pipeline used to reduce the DEIMOS data was developed at UC Berkeley with support from NSF grant AST-0071048. The authors thank A. McConnachie for use of the PAndAS image. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013, 2018). Facility: Keck:II (DEIMOS). Software: Astropy (Astropy Collaboration et al. 2013), Matplotlib (Hunter 2007), numpy (van der Walt et al. 2011).
Group:Astronomy Department
Funding AgencyGrant Number
Cottrell Scholar of Research CorporationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1745301
NASA Hubble Fellowship51386.01
NASANAS 5-26555
W. M. Keck FoundationUNSPECIFIED
Carnegie-Princeton FellowshipUNSPECIFIED
Subject Keywords:Galaxies ; Local Group; Andromeda Galaxy ; Galaxy stellar halos ; Stellar abundances
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Galaxies (573); Local Group (929); Andromeda Galaxy (39); Galaxy stellar halos (598); Stellar abundances (1577)
Record Number:CaltechAUTHORS:20200626-103612106
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Official Citation:Karoline M. Gilbert et al 2020 AJ 160 41
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104070
Deposited By: George Porter
Deposited On:26 Jun 2020 19:14
Last Modified:26 Jun 2020 19:14

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