Blanco DECam Bulge Survey (BDBS) IV: Metallicity distributions and bulge structure from 2.6 million red clump stars
Date Issued
2022
Author(s)
Johnson C.I.
Rich R.M.
Simion I.T.
Young M.D.
Clarkson W.I.
Pilachowski C.A.
Michael S.
Marchetti T.
Kunder A.
Koch-Hansen A.J.
Katherina Vivas A.
Joyce M.
Shen J.
Osmond A.
DOI
http://dx.doi.org/10.1093/mnras/stac1840
Abstract
We present photometric metallicity measurements for a sample of 2.6 million bulge red clump stars extracted from the Blanco DECam Bulge Survey (BDBS). Similar to previous studies, we find that the bulge exhibits a strong vertical metallicity gradient, and that at least two peaks in the metallicity distribution functions appear at b < -5°. We can discern a metal-poor ([Fe/H] ∼-0.3) and metal-rich ([Fe/H] ∼+0.2) abundance distribution that each show clear systematic trends with latitude, and may be best understood by changes in the bulge's star formation/enrichment processes. Both groups exhibit asymmetric tails, and as a result we argue that the proximity of a star to either peak in [Fe/H] space is not necessarily an affirmation of group membership. The metal-poor peak shifts to lower [Fe/H] values at larger distances from the plane while the metal-rich tail truncates. Close to the plane, the metal-rich tail appears broader along the minor axis than in off-axis fields. We also posit that the bulge has two metal-poor populations - one that belongs to the metal-poor tail of the low latitude and predominantly metal-rich group, and another belonging to the metal-poor group that dominates in the outer bulge. We detect the X-shape structure in fields with
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