The Metal-poor Metallicity Distribution of the Ancient Milky Way
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Chiti_2021_ApJL_911_L23.pdf
Description
Published version
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683.97 KB
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Author(s)
Chiti, Anirudh
Mardini, Mohammad K.
Frebel, Anna
Daniel, Tatsuya
Date Issued
April 2021
Journal
Astrophysical Journal Letters
Publisher
American Astronomical Society
Citation
Chiti, Anirudh, Mardini, Mohammad K, Frebel, Anna and Daniel, Tatsuya. 2021. "The Metal-poor Metallicity Distribution of the Ancient Milky Way." The Astrophysical Journal Letters, 911 (2).
Version
Final published version
Abstract
We present a low-metallicity map of the Milky Way consisting of ∼110,000 metal-poor giants with −3.5 < [Fe/H] < −0.75, based on public photometry from the second data release of the SkyMapper survey. These stars extend out to ∼7 kpc from the solar neighborhood and cover the main Galactic stellar populations, including the thick disk and the inner halo. Notably, this map can reliably differentiate metallicities down to [Fe/H] ∼ −3.0, and thus provides an unprecedented view into the ancient, metal-poor Milky Way. Among the more metal-rich stars in our sample ([Fe/H] > −2.0), we recover a clear spatial dependence of decreasing mean metallicity as a function of scale height that maps onto the thick disk component of the Milky Way. When only considering the very metal-poor stars in our sample ([Fe/H] < −2), we recover no such spatial dependence in their mean metallicity out to a scale height of ∣Z∣ ∼ 7 kpc. We find that the metallicity distribution function (MDF) of the most metal-poor stars in our sample (−3.0 < [Fe/H] < −2.3) is well fit with an exponential profile with a slope of and ${\rm{\Delta }}\mathrm{log}(N)/{\rm{\Delta }}$[Fe/H] = 1.52 ± 0.05, and slightly shifts to ${\rm{\Delta }}\mathrm{log}(N)/{\rm{\Delta }}[\mathrm{Fe}/{\rm{H}}]=1.53\pm 0.10$ after accounting for target selection effects. For [Fe/H] < −2.3, the MDF is largely insensitive to scale height ∣Z∣ out to ∼5 kpc, showing that very and extremely metal-poor stars are in every galactic component.
MIT Department
Massachusetts Institute of Technology. Department of Physics
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.3847/2041-8213/abd629
