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Elemental Abundances in M31: Gradients in the Giant Stellar Stream

Escala, Ivanna and Gilbert, Karoline M. and Wojno, Jennifer and Kirby, Evan N. and Guhathakurta, Puragra (2021) Elemental Abundances in M31: Gradients in the Giant Stellar Stream. Astronomical Journal, 162 (2). Art. No. 45. ISSN 0004-6256. doi:10.3847/1538-3881/abfec4.

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We analyze existing measurements of [Fe/H] and [α/Fe] for individual red giant branch (RGB) stars in the Giant Stellar Stream (GSS) of M31 to determine whether spatial abundance gradients are present. These measurements were obtained from low- (R ~ 3000) and moderate- (R ~ 6000) resolution Keck/DEIMOS spectroscopy using spectral synthesis techniques as part of the Elemental Abundances in M31 survey. From a sample of 62 RGB stars spanning the GSS at 17, 22, and 33 projected kpc, we measure a [Fe/H] gradient of −0.018 ± 0.003 dex kpc⁻¹ and negligible [α/Fe] gradient with M31-centric radius. We investigate GSS abundance patterns in the outer halo using additional [Fe/H] and [α/Fe] measurements for six RGB stars located along the stream at 45 and 58 projected kpc. These abundances provide tentative evidence that the trends in [Fe/H] and [α/Fe] beyond 40 kpc in the GSS are consistent with those within 33 kpc. We also compare the GSS abundances to 65 RGB stars located along the possibly related Southeast (SE) shelf substructure at 12 and 18 projected kpc. The abundances of the GSS and SE shelf are consistent, supporting a common origin hypothesis, although this interpretation may be complicated by the presence of [Fe/H] gradients in the GSS. We discuss the abundance patterns in the context of photometric studies from the literature and explore implications for the properties of the GSS progenitor, suggesting that the high 〈[α/Fe]〉 of the GSS (+0.40 ± 0.05 dex) favors a major merger scenario for its formation.

Item Type:Article
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URLURL TypeDescription Paper
Escala, Ivanna0000-0002-9933-9551
Gilbert, Karoline M.0000-0003-0394-8377
Wojno, Jennifer0000-0002-3233-3032
Kirby, Evan N.0000-0001-6196-5162
Guhathakurta, Puragra0000-0001-8867-4234
Additional Information:© 2021. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 March 15; revised 2021 May 4; accepted 2021 May 5; published 2021 July 6. We thank the anonymous referee, whose careful reading of this paper improved its clarity. We thank Emily C. Cunningham for helpful comments on the manuscript and Stephen Gwyn for reducing the photometry for slitmask f123_1. I.E. was generously supported by a Carnegie-Princeton Fellowship through the Carnegie Observatories. This material is based upon work supported by the NSF under grants Nos. AST-1614081 (E.N.K.), AST-1614569 (K.M.G, J.W.), and AST-1412648 (P.G.). 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. We are grateful to the many people who have worked to make the Keck Telescope and its instruments a reality and to operate and maintain the Keck Observatory. 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. Facility: Keck (DEIMOS). Software: Astropy (Astropy Collaboration et al. 2013, 2018), emcee (Foreman-Mackey et al. 2013).
Group:Astronomy Department
Funding AgencyGrant Number
Carnegie-Princeton FellowshipUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
Subject Keywords:Stellar abundances; Galaxy abundances; Stellar streams; Galaxy stellar halos; Andromeda Galaxy; Galaxy formation
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Stellar abundances (1577); Galaxy abundances (574); Stellar streams (2166); Galaxy stellar halos (598); Andromeda Galaxy (39); Galaxy formation (595)
Record Number:CaltechAUTHORS:20210709-222308921
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Official Citation:Ivanna Escala et al 2021 AJ 162 45
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109770
Deposited By: George Porter
Deposited On:09 Jul 2021 22:38
Last Modified:16 Nov 2021 19:37

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