Elemental Abundances in M31: Individual and Coadded Spectroscopic [Fe/H] and [α/Fe] throughout the M31 Halo with SPLASH

J. Leigh Wojno; Karoline M. Gilbert; Evan N. Kirby; Ivanna Escala; Puragra Guhathakurta; Rachael L. Beaton; Jason Kalirai; Masashi Chiba; Steven R. Majewski

doi:10.3847/1538-4357/acd5d3

The Astrophysical Journal (Jan 2023)

Elemental Abundances in M31: Individual and Coadded Spectroscopic [Fe/H] and [α/Fe] throughout the M31 Halo with SPLASH

J. Leigh Wojno,
Karoline M. Gilbert,
Evan N. Kirby,
Ivanna Escala,
Puragra Guhathakurta,
Rachael L. Beaton,
Jason Kalirai,
Masashi Chiba,
Steven R. Majewski

Affiliations

J. Leigh Wojno: ORCiD; The William H. Miller III Department of Physics & Astronomy, Bloomberg Center for Physics and Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218, USA ; [email protected]; Max-Planck Institute for Astronomy , Königstuhl 17, D-69117 Heidelberg, Germany
Karoline M. Gilbert: ORCiD; The William H. Miller III Department of Physics & Astronomy, Bloomberg Center for Physics and Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218, USA ; [email protected]; Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USA
Evan N. Kirby: ORCiD; Department of Physics and Astronomy, University of Notre Dame , Notre Dame, IN 46556, USA
Ivanna Escala: ORCiD; Department of Astrophysical Sciences, Princeton University , 4 Ivy Lane, Princeton, NJ 08544, USA; The Observatories of the Carnegie Institution for Science , 813 Santa Barbara Street, Pasadena, CA 91101, USA
Puragra Guhathakurta: ORCiD; Department of Astronomy & Astrophysics, University of California , Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
Rachael L. Beaton: ORCiD; The William H. Miller III Department of Physics & Astronomy, Bloomberg Center for Physics and Astronomy, Johns Hopkins University , 3400 N. Charles Street, Baltimore, MD 21218, USA ; [email protected]; Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USA
Jason Kalirai: ORCiD; Johns Hopkins Applied Physics Laboratory , 11101 Johns Hopkins Road, Laurel, MD 20723, USA
Masashi Chiba: ORCiD; Astronomical Institute, Tohoku University , Aoba-ku, Sendai 980-8578, Japan
Steven R. Majewski: ORCiD; Department of Astronomy, University of Virginia , Charlottesville, VA 22904-4325, USA

DOI: https://doi.org/10.3847/1538-4357/acd5d3
Journal volume & issue: Vol. 951, no. 1
p. 12

Abstract

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We present spectroscopic chemical abundances of red giant branch stars in Andromeda (M31), using medium-resolution ( R ∼ 6000) spectra obtained via the Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo survey. In addition to individual chemical abundances, we coadd low signal-to-noise ratio spectra of stars to obtain a high enough signal to measure average [Fe/H] and [ α /Fe] abundances. We obtain individual and coadded measurements for [Fe/H] and [ α /Fe] for M31 halo stars, covering a range of 9–180 kpc in projected radius from the center of M31. With these measurements, we greatly increase the number of outer halo ( R _proj > 50 kpc) M31 stars with spectroscopic [Fe/H] and [ α /Fe], adding abundance measurements for 45 individual stars and 33 coadds from a pool of an additional 174 stars. We measure the spectroscopic metallicity ([Fe/H]) gradient, finding a negative radial gradient of −0.0084 ± 0.0008 for all stars in the halo, consistent with gradient measurements obtained using photometric metallicities. Using the first measurements of [ α /Fe] for M31 halo stars covering a large range of projected radii, we find a positive gradient (+0.0027 ± 0.0005) in [ α /Fe] as a function of projected radius. We also explore the distribution in [Fe/H]–[ α /Fe] space as a function of projected radius for both individual and coadded measurements in the smooth halo, and compare these measurements to those stars potentially associated with substructure. These spectroscopic abundance distributions add to existing evidence that M31 has had an appreciably different formation and merger history compared to our own Galaxy.

Published in The Astrophysical Journal

ISSN: 1538-4357 (Online)
Publisher: IOP Publishing
Country of publisher: United Kingdom
LCC subjects: Science: Astronomy: Astrophysics
Website: https://iopscience.iop.org/journal/0004-637X

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