Stellar Metallicities from SkyMapper Photometry II: Precise photometric metallicities of $sim$280,000 giant stars with [Fe/H] $< -0.75$ in the Milky Way

Kavli Affiliate: Anna Frebel

| First 5 Authors: Anirudh Chiti, Anna Frebel, Mohammad K. Mardini, Tatsuya W. Daniel, Xiaowei Ou

| Summary:

The Milky Way’s metal-poor stars are nearby ancient objects that are used to
study early chemical evolution and the assembly and structure of the Milky Way.
Here we present reliable metallicities of $sim280,000$ stars with $-3.75
lesssim$ [Fe/H] $lesssim -0.75$ down to $g=17$ derived using
metallicity-sensitive photometry from the second data release (DR2) of the
SkyMapper Southern Survey. We use the dependency of the flux through the
SkyMapper $v$ filter on the strength of the Ca II K absorption features, in
tandem with SkyMapper $u,g,i$ photometry, to derive photometric metallicities
for these stars. We find that metallicities derived in this way compare well to
metallicities derived in large-scale spectroscopic surveys, and use such
comparisons to calibrate and quantify systematics as a function of location,
reddening, and color. We find good agreement with metallicities from the
APOGEE, LAMOST, and GALAH surveys, based on a standard deviation of
$sigmasim0.25$dex of the residuals of our photometric metallicities with
respect to metallicities from those surveys. We also compare our derived
photometric metallicities to metallicities presented in a number of
high-resolution spectroscopic studies to validate the low metallicity end
([Fe/H] $< -2.5$) of our photometric metallicity determinations. In such
comparisons, we find the metallicities of stars with photometric [Fe/H] $<
-2.5$ in our catalog show no significant offset and a scatter of
$sigmasim$0.31dex level relative to those in high-resolution work when
considering the cooler stars ($g-i > 0.65$) in our sample. We also present an
expanded catalog containing photometric metallicities of $sim720,000$ stars as
a data table for further exploration of the metal-poor Milky Way.

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