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

By Matthieu Portail, O. Gerhard, C. Wegg, Melissa Ness Max-Planck-Institut fuer Extraterrestrische Physik, M. F. Astronomie. 2016

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We construct a large set of dynamical models of the galactic bulge, bar and inner disk 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 $39.0 \pm 3.5 \,\rm{km\,s^{-1}\,kpc^{-1}}$, placing the bar corotation radius at $6.1 \pm 0.5 \rm{kpc}$ and making the Milky Way bar a typical fast rotator. We evaluate the stellar mass of the long bar and bulge structure to be $M_{\rm{bar/bulge}} = 1.88 \pm 0.12 \times 10^{10} \, \rm{M}_{\odot}$, larger than the mass of disk in the bar region, $M_{\rm{inner\ disk}} = 1.29\pm0.12 \times 10^{10} \, \rm{M}_{\odot}$. The total dynamical mass in the bulge volume is $1.85\pm0.05\times 10^{10} \, \rm{M}_{\odot}$. Thanks to more extended kinematic data sets and recent measurement of the bulge IMF our models have a low dark matter fraction in the bulge of $17\%\pm2\%$. 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 $\sim0.2\times10^{10} \,\rm{M}_{\odot}$, probably in a nuclear disk or disky pseudobulge.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/4b578980a956d2af9845e56713894191c6031d83

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The milky way total mass profile as inferred from Gaia DR2 (2019, background): “Also, for the same reason we do not model the complicated geometry of the stellar distribution at the centre of the MW, i.e. peanut bulge and bar (e.g. Portail et al. 2017), since it has only minor effects on the gravitational field at R > 5 kpc.”