A Caltech Library Service

Where are the most ancient stars in the Milky Way?

El-Badry, Kareem and Bland-Hawthorn, Joss and Wetzel, Andrew and Quataert, Eliot and Weisz, Daniel R. and Boylan-Kolchin, Michael and Hopkins, Philip F. and Faucher-Giguère, Claude-André and Kereš, Dušan and Garrison-Kimmel, Shea (2018) Where are the most ancient stars in the Milky Way? Monthly Notices of the Royal Astronomical Society, 480 (1). pp. 652-668. ISSN 0035-8711. PMCID PMC6301095.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.

[img] PDF (PubMed Central) - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


The oldest stars in the Milky Way (MW) bear imprints of the Galaxy’s early assembly history. We use FIRE cosmological zoom-in simulations of three MW-mass disc galaxies to study the spatial distribution, chemistry, and kinematics of the oldest surviving stars (z_(form) ≳ 5) in MW-like galaxies. We predict the oldest stars to be less centrally concentrated at z = 0 than stars formed at later times as a result of two processes. First, the majority of the oldest stars are not formed in situ but are accreted during hierarchical assembly. These ex situ stars are deposited on dispersion-supported, halo-like orbits but dominate over old stars formed in situ in the solar neighbourhood, and in some simulations, even in the galactic centre. Secondly, old stars formed in situ are driven outwards by bursty star formation and energetic feedback processes that create a time-varying gravitational potential at z ≳ 2, similar to the process that creates dark matter cores and expands stellar orbits in bursty dwarf galaxies. The total fraction of stars that are ancient is more than an order of magnitude higher for sight lines away from the bulge and inner halo than for inward-looking sight lines. Although the task of identifying specific stars as ancient remains challenging, we anticipate that million-star spectral surveys and photometric surveys targeting metal-poor stars already include hundreds of stars formed before z = 5. We predict most of these targets to have higher metallicity (-3 < [Fe/H] < -2) than the most extreme metal-poor stars.

Item Type:Article
Related URLs:
URLURL TypeDescription CentralArticle Paper
El-Badry, Kareem0000-0002-6871-1752
Bland-Hawthorn, Joss0000-0001-7516-4016
Wetzel, Andrew0000-0003-0603-8942
Quataert, Eliot0000-0001-9185-5044
Weisz, Daniel R.0000-0002-6442-6030
Boylan-Kolchin, Michael0000-0002-9604-343X
Hopkins, Philip F.0000-0003-3729-1684
Faucher-Giguère, Claude-André0000-0002-4900-6628
Kereš, Dušan0000-0002-1666-7067
Garrison-Kimmel, Shea0000-0002-4655-8128
Additional Information:© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2018 July 8. Received 2018 June 1; in original form 2018 April 2. Published: 14 July 2018. We have benefited from fruitful discussions with K.C. Freeman, A. Karakas, S. Loebman, C.F. McKee, and S. Tabin. KE acknowledges support from a Berkeley graduate fellowship, a Hellman award for graduate study, and an NSF Graduate Research Fellowship. JBH acknowledges a Miller Professorship from the Miller Institute, UC Berkeley. JBH is also supported by an ARC Laureate Fellowship from the Australian Government. AW was supported by NASA through grants HST-GO-14734 and HST-AR-15057 from STScI. EQ and KE are supported by a Simons Investigator Award from the Simons Foundation and by NSF grant AST-1715070. DRW is supported by a fellowship provided by the Alfred P. Sloan Foundation. MBK acknowledges support from NSF grant AST-1517226 and CAREER grant AST-1752913 and from NASA grants NNX17AG29G and HST-AR-13888, HST-AR-13896, HST-AR-14282, HST-AR-14554, HST-AR-15006, HST-GO-12914, and HST-GO-14191 from STScI. Support for PFH was provided by an Alfred P. Sloan Research Fellowship, NASA ATP Grant NNX14AH35G, and NSF Collaborative Research Grant #1411920 and CAREER grant #1455342. CAFG was supported by NSF through grants AST-1412836, AST-1517491, AST-1715216, and CAREER award AST-1652522, by NASA through grant NNX15AB22G, and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. DK was supported by NSF grants AST-1412153 and AST-1715101 and the Cottrell Scholar Award from the Research Corporation for Science Advancement. Support for SGK was provided by NASA through Einstein Postdoctoral Fellowship grant number PF5-160136 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. We ran numerical calculations on the Caltech compute cluster ‘Wheeler,’ allocations TG-AST130039 & TG-AST150080 granted by the Extreme Science and Engineering Discovery Environment (XSEDE) supported by the NSF, and the NASA HEC Program through the NAS Division at Ames Research Center and the NCCS at Goddard Space Flight Center. The analysis in this paper relied on the PYTHON packages NumPy (Van Der Walt, Colbert & Varoquaux 2011), Matplotlib (Hunter 2007), and AstroPy (Astropy Collaboration 2013).
Group:TAPIR, Astronomy Department
Funding AgencyGrant Number
University of California, BerkeleyUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Australian Research CouncilUNSPECIFIED
Simons FoundationUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
NASA Einstein FellowshipPF5-160136
Subject Keywords:Galaxy: evolution – Galaxy: formation – Galaxy: stellar content
Issue or Number:1
PubMed Central ID:PMC6301095
Record Number:CaltechAUTHORS:20180912-153417896
Persistent URL:
Official Citation:Kareem El-Badry, Joss Bland-Hawthorn, Andrew Wetzel, Eliot Quataert, Daniel R Weisz, Michael Boylan-Kolchin, Philip F Hopkins, Claude-André Faucher-Giguère, Dušan Kereš, Shea Garrison-Kimmel; Where are the most ancient stars in the Milky Way?, Monthly Notices of the Royal Astronomical Society, Volume 480, Issue 1, 11 October 2018, Pages 652–668,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89597
Deposited By: Tony Diaz
Deposited On:12 Sep 2018 23:29
Last Modified:07 Apr 2020 17:29

Repository Staff Only: item control page