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Elemental Abundances in M31: First Alpha and Iron Abundance Measurements in M31's Giant Stellar Stream

Gilbert, Karoline M. and Kirby, Evan N. and Escala, Ivanna and Wojno, Jennifer and Kalirai, Jason S. and Guhathakurta, Puragra (2019) Elemental Abundances in M31: First Alpha and Iron Abundance Measurements in M31's Giant Stellar Stream. Astrophysical Journal, 883 (2). Art. No. 128. ISSN 1538-4357. doi:10.3847/1538-4357/ab3807.

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We present the first measurements of [Fe/H] and [α/Fe] abundances, obtained using spectral synthesis modeling, for red giant branch stars in M31's giant stellar stream (GSS). The spectroscopic observations, obtained at a projected distance of 17 kpc from M31's center, yielded 61 stars with [Fe/H] measurements, including 21 stars with [α/Fe] measurements, from 112 targets identified as M31 stars. The [Fe/H] measurements confirm the expectation from photometric metallicity estimates that stars in this region of M31's halo are relatively metal rich compared to stars in the Milky Way's inner halo: more than half the stars in the field, including those not associated with kinematically identified substructure, have [Fe/H] abundances >-1.0. The stars in this field are α-enhanced at lower metallicities, while [α/Fe] decreases with increasing [Fe/H] above metallicities of [Fe/H] ≳ −0.9. Three kinematical components have been previously identified in this field: the GSS, a second kinematically cold feature of unknown origin, and M31's kinematically hot halo. We compare probabilistic [Fe/H] and [α/Fe] distribution functions for each of the components. The GSS and the second kinematically cold feature have very similar abundance distributions, while the halo component is more metal poor. Although the current sample sizes are small, a comparison of the abundances of stars in the GSS field with abundances of M31 halo and dSph stars from the literature indicate that the progenitor of the stream was likely more massive, and experienced a higher efficiency of star formation, than M31's existing dSphs or the dEs NGC 147 and NGC 185.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Gilbert, Karoline M.0000-0003-0394-8377
Kirby, Evan N.0000-0001-6196-5162
Escala, Ivanna0000-0002-9933-9551
Wojno, Jennifer0000-0002-3233-3032
Kalirai, Jason S.0000-0001-9690-4159
Guhathakurta, Puragra0000-0001-8867-4234
Additional Information:© 2019 The American Astronomical Society. Received 2019 April 30; revised 2019 July 31; accepted 2019 July 31; published 2019 September 26. 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. The authors thank M. Fardal, F. Hammer, Y. Yang, and S. Hasselquist for helpful conversations during the writing of this manuscript, and 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). Support for this work was provided by NSF grants AST-1614569 (K.M.G., J.W.), AST-1614081 (E.N.K., I.E.), 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. I.E. acknowledges support from a National Science Foundation (NSF) Graduate Research Fellowship under grant No. DGE-1745301. The analysis pipeline used to reduce the DEIMOS data was developed at UC Berkeley with support from NSF grant AST-0071048. Facilities: Keck II (DEIMOS) - , CFHT (MegaCam). - Software: Astropy (Astropy Collaboration et al. 2013), Matplotlib (Hunter 2007), numpy (van der Walt et al. 2011), corner (Foreman-Mackey 2016; Foreman-Mackey et al. 2016a).
Group:Astronomy Department
Funding AgencyGrant Number
Cottrell Scholar of Research CorporationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1745301
Subject Keywords:galaxies: halos – galaxies: individual (M31) – stars: abundances – stars: kinematics and dynamics – techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:20190927-092802684
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Official Citation:Karoline M. Gilbert et al 2019 ApJ 883 128
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98901
Deposited By: Tony Diaz
Deposited On:27 Sep 2019 17:41
Last Modified:16 Nov 2021 17:42

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