Matthieu Portail

The structure of the Milky Way's bar outside the bulge

While it is incontrovertible that the inner Galaxy contains a bar, its structure near the Galactic plane has remained uncertain, where extinction from intervening dust is greatest. We investigate here the Galactic bar outside the bulge, the long bar, using red clump giant (RCG) stars from UKIDSS, 2MASS, VVV, and GLIMPSE. We match and combine these surveys to investigate a wide area in latitude and longitude, |b|<9deg and |l|<40deg. We find: (1) The bar extends to l~25deg at |b|~5deg from the Galactic plane, and to l~30deg at lower latitudes. (2) The long bar has an angle to the line-of-sight in the range (28-33)deg, consistent with studies of the bulge at |l|<10deg. (3) The scale-height of RCG stars smoothly transitions from the bulge to the thinner long bar. (4) There is evidence for two scale heights in the long bar. We find a ~180pc thin bar component reminiscent of the old thin disk near the sun, and a ~45pc super-thin bar component which exists predominantly towards the bar end. (5) Constructing parametric models for the RC magnitude distributions, we find a bar half length of 5.0+-0.2kpc for the 2-component bar, and 4.6+-0.3kpc for the thin bar component alone. We conclude that the Milky Way contains a central box/peanut bulge which is the vertical extension of a longer, flatter bar, similar as seen in both external galaxies and N-body models.

Made-to-measure models of the Galactic box/peanut bulge: stellar and total mass in the bulge region

We construct dynamical models of the Milky Ways Box/Peanut (B/P) bulge, using the recently measured 3D density of Red Clump Giants (RCGs) as well as kinematic data from the BRAVA survey. We match these data using the NMAGIC Made-to-Measure method, starting with N-body models for barred discs in different dark matter haloes. We determine the total mass in the bulge volume of the RCGs measurement (+-2.2 x +- 1.4 x +- 1.2 kpc) with unprecedented accuracy and robustness to be 1.84 +- 0.07 x10^10 Msun. The stellar mass in this volume varies between 1.25-1.6 x10^10 Msun, depending on the amount of dark matter in the bulge. We evaluate the mass-to-light and mass-to-clump ratios in the bulge and compare them to theoretical predictions from population synthesis models. We find a mass-to-light ratio in the K-band in the range 0.8-1.1. The models are consistent with a Kroupa or Chabrier IMF, but a Salpeter IMF is ruled out for stellar ages of 10 Gyr. To match predictions from the Zoccali IMF derived from the bulge stellar luminosity function requires about 40% or 0.7 x10^10 Msun dark matter in the bulge region. The BRAVA data together with the RCGs 3D density imply a low pattern speed for the Galactic B/P bulge of 25-30 km.s-1.kpc-1. This would place the Galaxy among the slow rotators (R >= 1.5). Finally, we show that the Milky Ways B/P bulge has an off-centred X structure, and that the stellar mass involved in the peanut shape accounts for at least 20% of the stellar mass of the bulge, significantly larger than previously thought.

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 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

Gas dynamics in the Milky Way: a low pattern speed model

39.0 \pm 3.5 \,\rm{km\,s^{-1}\,kpc^{-1}}

Revisiting the Tale of Hercules: How Stars Orbiting the Lagrange Points Visit the Sun

, placing the bar corotation radius at

MOA-II Galactic microlensing constraints: the inner Milky Way has a low dark matter fraction and a near maximal disc

6.1 \pm 0.5 \rm{kpc}

Chemodynamical modelling of the galactic bulge and bar

and making the Milky Way bar a typical fast rotator. We evaluate the stellar mass of the long bar and bulge structure to be

The Stellar Halo in the Inner Milky Way: Predicted Shape and Kinematics

M_{\rm{bar/bulge}} = 1.88 \pm 0.12 \times 10^{10} \, \rm{M}_{\odot}

Andromeda chained to the box - dynamical models for M31: bulge and bar

, larger than the mass of disk in the bar region,

The initial mass function of the inner galaxy measured from OGLE-III microlensing timescales

M_{\rm{inner\ disk}} = 1.29\pm0.12 \times 10^{10} \, \rm{M}_{\odot}