http://arxiv.org/abs/1801.01426
Despite the huge amount of photometric and spectroscopic efforts targetting the Galactic bulge over the past few years, its age distribution remains controversial owing to both the complexity of determining the age of individual stars and the difficult observing conditions. Taking advantage of the recent release of very deep, proper-motion-cleaned colour–magnitude diagrams (CMDs) of four low reddening windows obtained with the Hubble Space Telescope (HST), we used the CMD-fitting technique to calculate the star formation history (SFH) of the bulge at -2deg > b > -4deg along the minor axis. We find that over 80% of the stars formed before 8 Gyr ago, but that a significant fraction of the super-solar metallicity stars are younger than this age. Considering only the stars that are within reach of the current generation of spectrographs (i.e. V < 21), we find that 11% of the bulge stars are younger than 5 Gyr, while this fraction rises to 30-40% in the metal-rich peak. The age-metallicity relation is well parametrized by a linear fit implying an enrichment rate of dZ/dt ~ 0.007 Gyr$^{-1}$. Our metallicity distribution function accurately reproduces that observed by several spectroscopic surveys of Baade’s window, with the bulk of stars having metal-content in the range [Fe/H] ~ -0.7 to ~0.6, along with a sparse tail to much lower metallicities.
E. Bernard, M. Schultheis, P. Matteo, et. al.
Mon, 8 Jan 18
93/117
Comments: Submitted to MNRAS. Comments welcome