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

By Matthieu Portail, C. Wegg, O. Gerhard, I. Martinez-Valpuesta. 2015

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We construct dynamical models of the Milky Way's 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 Way's 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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/29a070eaf17dcd659ba494f1d7b4162021b5dc15

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Citations in the corpus

Dynamical modelling of the galactic bulge and bar: the Milky Way's pattern speed, stellar and dark matter mass distribution (2016, methodology): “(ii) We find a total dynamical mass of the bulge of 1.85± 0.05× 1010 M , in excellent agreement with the value found in Portail et al. (2015a) from modelling the bulge only.”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, methodology): “Data from Wegg & Gerhard (2013); figure after Portail et al. (2015b).”
Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy (2016, background): “The total mass of the Galactic bulge is estimated to be ∼ 2 × 1010 M⊙ (Sofue et al. 2009), with a stellar mass ranging somewhere between 1.25 and 1.6×1010 M⊙ (Portail et al. 2015).”
THE SINFONI BLACK HOLE SURVEY: THE BLACK HOLE FUNDAMENTAL PLANE REVISITED AND THE PATHS OF (CO)EVOLUTION OF SUPERMASSIVE BLACK HOLES AND BULGES (2016, unknown): “Portail et al. (2015) compute the total mass in the bulge volume (±2.2×±1.4×±1.2) kpc to be 1.84 × 1010M .”
On the estimation of the local dark matter density using the rotation curve of the Milky Way (2019, methodology): “[22]), so a spherical approximation can be used as long as we do not include data at R .”
The mass distribution and gravitational potential of the Milky Way (2016, methodology): “Portail et al.(2015) used Made-To-Measure modelling to determine the mass within a box around the Galactic centre of a volume (±2.2 ± 1.4 ± 1.2) kpc, determining that it is (1.84 ± 0.07) × 1010 M⊙ (and the closely related study byPortail et al. 2016, found a very similar value – (1.85± 0.05)× 1010…”
The structure of the Milky Way's bar outside the bulge (2015, methodology): “The inner cutoff is required because the N-body model already fits the magnitude distributions in the central region well as it was tailored to fit the data there using the made-to-measure method in Portail et al. (2015).”