Published in Publications of the Astronomical Society of Australia, Volume 33, id.e022, 2016.
https://arxiv.org/abs/1511.07438

For a PDF version of the article, click here.

THE METALLICITY DISTRIBUTION OF THE MILKY WAY BULGE

M. Ness 1 and K. Freeman 2


1 Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
2 Research School of Astronomy and Astrophysics, Australian National University, Cotter Rd., Weston, ACT 2611, Australia


Abstract: The Galactic bulge of the Milky Way is made up of stars with a broad range of metallicity, –3.0 < [Fe/H] < 1 dex. The mean of the Metallicity Distribution Function (MDF) decreases as a function of height z from the plane and, more weakly, with galactic radius RGC. The most metal rich stars in the inner Galaxy are concentrated to the plane and the more metal poor stars are found predominantly further from the plane, with an overall vertical gradient in the mean of the MDF of about —0.45 dex/kpc. This vertical gradient is believed to reflect the changing contribution with height of different populations in the inner-most region of the Galaxy. The more metal rich stars of the bulge are part of the boxy/peanut structure and comprise stars in orbits which trace out the underlying X-shape. There is still a lack of consensus on the origin of the metal poor stars ([Fe/H] < −0.5) in the region of the bulge. Some studies attribute the more metal poor stars of the bulge to the thick disk and stellar halo that are present in the inner region, and other studies propose that the metal poor stars are a distinct ‘old spheroid' bulge population. Understanding the origin of the populations that make up the MDF of the bulge, and identifying if there is a unique bulge population which has formed separately from the disk and halo, has important consequences for identifying the relevant processes in the the formation and evolution of the Milky Way.

Keywords: The Galaxy – bulge – abundances – formation – evolution


Table of Contents

THE GLOBAL MDF OF THE BULGE

MULTIPLE STELLAR POPULATIONS IN THE BULGE

THE ALPHA-ENHANCEMENT OF THE BULGE

THE METAL POOR [FE/H] < -1.0 POPULATION

CONCLUSIONS

REFERENCES

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