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We use data of $sim$13,000 stars from the SDSS/APOGEE survey to study the shape of the bulge MDF within the region $|ell|leq11^circ$ and $|b|leq13^circ$, and spatially constrained to ${rm R_{GC}leq3.5}$ kpc. We apply Gaussian Mixture Modeling and Non-negative Matrix Factorization decomposition techniques to identify the optimal number and the properties of MDF components. We find the shape and spatial variations of the MDF (at ${rm [Fe/H]geq-1}$ dex) are well represented as a smoothly varying contribution of three overlapping components located at [Fe/H]=+$0.32$, $-0.17$ and $-0.66$ dex. The bimodal MDF found in previous studies is in agreement with our trimodal assessment once the limitations in sample size and individual measurement errors are taken into account. The shape of the MDF and its correlations with kinematics reveal different spatial distributions and kinematical structure for the three components co-existing in the bulge region. We confirm the consensus physical interpretation of metal-rich stars as associated with the secularly evolved disk into a boxy/peanut X-shape bar. On the other hand, metal-intermediate stars could be the product of in-situ formation at high redshift in a gas-rich environment characterized by violent and fast star formation. This interpretation would help to link a present-day structure with those observed in formation in the center of high redshift galaxies. Finally, metal-poor stars may correspond to the metal-rich tail of the population sampled at lower metallicity from the study of RR Lyrae stars. Conversely, they could be associated with the metal-poor tail of the early thick disc.
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 galact
We present stellar age distributions of the Milky Way (MW) bulge region using ages for $sim$6,000 high-luminosity ($log(g) < 2.0$), metal-rich ($rm [Fe/H] ge -0.5$) bulge stars observed by the Apache Point Observatory Galactic Evolution Experiment (A
Using a sample of 69,919 red giants from the SDSS-III/APOGEE Data Release 12, we measure the distribution of stars in the [$alpha$/Fe] vs. [Fe/H] plane and the metallicity distribution functions (MDF) across an unprecedented volume of the Milky Way d
We present Galactic mean metallicity maps derived from the first year of the SDSS-III APOGEE experiment. Mean abundances in different zones of Galactocentric radius (0 < R < 15 kpc) at a range of heights above the plane (0 < |z| < 3 kpc), are derived
Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily-reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable e