A Parametric Galactic Model toward the Galactic Bulge Based on Gaia and Microlensing Data

Abstract

We developed a parametric Galactic model toward the Galactic bulge by fitting to spatial distributions of the Gaia DR2 disk velocity, VVV proper motion, BRAVA radial velocity, OGLE-III red clump star count, and OGLE-IV star count and microlens rate, optimized for use in microlensing studies. We include the asymmetric drift of Galactic disk stars and the dependence of velocity dispersion on Galactic location in the kinematic model, which has been ignored in most previous models used for microlensing studies. We show that our model predicts a microlensing parameter distribution significantly different from those typically used in previous studies. We estimate various fundamental model parameters for our Galaxy through our modeling, including the initial mass function (IMF) in the inner Galaxy. Combined constraints from star counts and the microlensing event timescale distribution from the OGLE-IV survey, in addition to a prior on the bulge stellar mass, enable us to successfully measure IMF slopes using a broken power-law form over a broad mass range, ${\alpha }_{\mathrm{bd}}=0.22_{-0.55}^{+0.20}$ for $M<0.08M_{\odot }$, ${\alpha }_{\mathrm{ms}}=1.16_{-0.15}^{+0.08}$ for $0.08M_{\odot }\le M<M_{\mathrm{br}}$, and ${\alpha }_{\mathrm{hm}}=2.32_{-0.10}^{+0.14}$ for $M\ge M_{\mathrm{br}}$, as well as a break mass at $M_{\mathrm{br}}=0.90_{-0.14}^{+0.05}{M}_{\odot }$. This is significantly different from the Kroupa IMF for local stars, but similar to the Zoccali IMF measured from a bulge luminosity function. We also estimate the dark matter mass fraction in the bulge region of $28\pm 7$\% which could be larger than a previous estimate. Because our model is purely parametric, it can be universally applied using the parameters provided in this paper.

47 pages, 13 figures, 7 tables, accepted to ApJ. A code for microlensing simulation using the developed Galactic model is available via https://github.com/nkoshimoto/genulens

References in corpus (31)

• Improving PARSEC models for very low mass stars
• New PARSEC evolutionary tracks of massive stars at low metallicity: testing canonical stellar evolution in nearby star forming dwarf galaxies
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• The Structure of the Milky Way's Bar Outside the Bulge
• No large population of unbound or wide-orbit Jupiter-mass planets
• The Initial-Final Mass Relation: Direct Constraints at the Low Mass End
• The Exoplanet Mass-Ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass
• Constraining the Galaxy's dark halo with RAVE stars
• Made-to-Measure models of the Galactic Box/Peanut bulge: stellar and total mass in the bulge region
• Modelling the Galactic bar using OGLE-II Red Clump Giant Stars
• Constraining the thick disc formation scenario of the Milky Way
• VIRAC: The VVV Infrared Astrometric Catalogue
• The Bulge Radial Velocity Assay (BRAVA): I. Techniques and a Rotation Curve
• Kinematic modelling of the Milky Way using the RAVE and GCS stellar surveys
• The Bulge Radial Velocity Assay (BRAVA): I. Sample Selection and a Rotation Curve
• Microlensing Results Challenge the Core Accretion Runaway Growth Scenario for Gas Giants
• Extended distribution functions for our Galaxy
• OGLE-III Microlensing Events and the Structure of the Galactic Bulge
• The age-velocity dispersion relation of the Galactic discs from LAMOST-Gaia data
• Red clump stars and Gaia: Calibration of the standard candle using a hierarchical probabilistic model
• MOA-II Galactic Microlensing Constraints: The Inner Milky Way has a Low Dark Matter Fraction and a Near Maximal Disk
• Kinematics of the local disk from the RAVE survey and the Gaia first data release
• PopSyCLE: A New Population Synthesis Code for Compact Object Microlensing Events
• Proper Motion Dispersions of Red Clump Giants in the Galactic Bulge: Observations and Model Comparisons
• Transverse kinematics of the Galactic bar-bulge from VVV and Gaia
• Mapping stellar kinematics across the Galactic bar: HST measurements of proper motions in 35 fields
• The Initial Mass Function of the Inner Galaxy Measured From OGLE-III Microlensing Timescales
• First Detection of the White-Dwarf Cooling Sequence of the Galactic Bulge
• OGLE-2008-BLG-355Lb: A Massive Planet around A Late type Star
• MaB$\mu$lS-2: high-precision microlensing modelling for the large-scale survey era
• Comparing Observed Stellar Kinematics and Surface Densities in a Low Latitude Bulge Field to Galactic Population Synthesis Models

Cited by in corpus (2)

• OGLE-2014-BLG-0319: A Sub-Jupiter-Mass Planetary Event Encountered Degeneracy with Different Mass Ratios and Lens-Source Relative Proper Motions
• New Giant Planet beyond the Snow Line for an Extended MOA Exoplanet Microlens Sample