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Elemental Abundances in M31: Alpha and Iron Element Abundances from Low-resolution Resolved Stellar Spectroscopy in the Stellar Halo

Escala, Ivanna and Kirby, Evan N. and Gilbert, Karoline M. and Cunningham, Emily C. and Wojno, Jennifer (2019) Elemental Abundances in M31: Alpha and Iron Element Abundances from Low-resolution Resolved Stellar Spectroscopy in the Stellar Halo. Astrophysical Journal, 878 (1). Art. No. 42. ISSN 1538-4357. doi:10.3847/1538-4357/ab1eac.

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Measurements of [Fe/H] and [α/Fe] can probe the minor merging history of a galaxy, providing a direct way to test the hierarchical assembly paradigm. While measurements of [α/Fe] have been made in the stellar halo of the Milky Way (MW), little is known about detailed chemical abundances in the stellar halo of M31. To make progress with existing telescopes, we apply spectral synthesis to low-resolution DEIMOS spectroscopy (R ~ 2500 at 7000 Å) across a wide spectral range (4500 Å < λ < 9100 Å). By applying our technique to low-resolution spectra of 170 giant stars in five MW globular clusters, we demonstrate that our technique reproduces previous measurements from higher resolution spectroscopy. Based on the intrinsic dispersion in [Fe/H] and [α/Fe] of individual stars in our combined cluster sample, we estimate systematic uncertainties of ~0.11 dex and ~0.09 dex in [Fe/H] and [α/Fe], respectively. We apply our method to deep, low-resolution spectra of 11 red giant branch stars in the smooth halo of M31, resulting in higher signal-to-noise ratios per spectral resolution element compared to DEIMOS medium-resolution spectroscopy, given the same exposure time and conditions. We find 〈[α/Fe]〉 = 0.49 ± 0.29 dex and 〈[Fe/H]〉 = −1.59 ± 0.56 dex for our sample. This implies that—much like the MW—the smooth halo field of M31 is likely composed of disrupted dwarf galaxies with truncated star formation histories that were accreted early in the halo's formation.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Escala, Ivanna0000-0002-9933-9551
Kirby, Evan N.0000-0001-6196-5162
Gilbert, Karoline M.0000-0003-0394-8377
Cunningham, Emily C.0000-0002-6993-0826
Wojno, Jennifer0000-0002-3233-3032
Additional Information:© 2019 The American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 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 2018 November 15; revised 2019 April 9; accepted 2019 April 30; published 2019 June 12. The authors thank the anonymous reviewer for a careful reading of this manuscript and providing thoughtful feedback that improved this paper. We also thank Alis Deason for assistance in line-list vetting, Gina Duggan for useful discussions on generating grids of synthetic spectra, Raja Guha Thakurta for help with observations and insightful conversations, and Luis Vargas and Marla Geha for sharing their data for M31 outer halo RGB stars. I.E. acknowledges support from a Ford Foundation Predoctoral Fellowship and the NSF Graduate Research Fellowship under grant No. DGE-1745301, as well as the NSF under grant No. AST-1614081, along with E.N.K. K.M.G. and J.W. acknowledge support from NSF grant AST-1614569. E.C.C. was supported by an NSF Graduate Research Fellowship as well as NSF grant No. AST-1616540. The analysis pipeline used to reduce the DEIMOS data was developed at UC Berkeley with support from NSF grant AST-0071048.
Group:Astronomy Department
Funding AgencyGrant Number
Ford FoundationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1745301
Subject Keywords:galaxies: abundances – galaxies: formation – galaxies: halos – Local Group – stars: abundances
Issue or Number:1
Record Number:CaltechAUTHORS:20190613-111030848
Persistent URL:
Official Citation:Ivanna Escala et al 2019 ApJ 878 42
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96387
Deposited By: Tony Diaz
Deposited On:13 Jun 2019 18:22
Last Modified:16 Nov 2021 17:20

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