Dynamical modelling of the galactic bulge and bar: the Milky Way's pattern speed, stellar and dark matter mass distribution

We construct a large set of dynamical models of the galactic bulge, bar and inner disc using the made-to-measure method. Our models are constrained to match the red clump giant density from a combination of the VVV, UKIDSS and 2MASS infrared surveys together with stellar kinematics in the bulge from the BRAVA and OGLE surveys, and in the entire bar region from the ARGOS Survey. We are able to recover the bar pattern speed and the stellar and dark matter mass distributions in the bar region, thus recovering the entire galactic effective potential. We find a bar pattern speed of 39.0 ± 3.5 km s^{- 1} kpc^{- 1}, placing the bar corotation radius at 6.1 ± 0.5 kpc and making the Milky Way bar a typical fast rotator. We evaluate the stellar mass of the long bar and bulge structure to be M_bar/bulge = 1.88 ± 0.12 × 10¹⁰ M_⊙, larger than the mass of disc in the bar region, M_{inner disc} = 1.29 ± 0.12 × 10¹⁰ M_⊙. The total dynamical mass in the bulge volume is 1.85 ± 0.05 × 10¹⁰ M_⊙. Thanks to more extended kinematic data sets and recent measurement of the bulge initial mass function, our models have a low dark matter fraction in the bulge of 17 ± 2 per cent. We find a dark matter density profile which flattens to a shallow cusp or core in the bulge region. Finally, we find dynamical evidence for an extra central mass of ∼ 0.2 × 10¹⁰ M_⊙, probably in a nuclear disc or discy pseudo-bulge.