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An Updated \synthpop Model for Microlensing Simulations I: Model Description, Evaluation, and Microlensing Event Rates Near the Galactic Center

Macy J. Huston, Alison L. Crisp, Marz Newman, Riley Patlak, Matthew T. Penny, Jonas Kluter, Peter McGill, Leigh C. Smith, Victor Karkour, Natasha S. Abrams, B. Scott Gaudi, Casey Y. Lam, Jessica R. Lu, Sebastiano Calchi Novati, Keivan G. Stassun, Sean K. Terry, Farzaneh Zohrabi

Abstract

The optimization and interpretation of microlensing surveys depends on having an accurate model of the Milky Way. However, existing Galactic modeling tools often perform poorly in replicating the stellar contents of the inner Galactic bulge region and reproducing microlensing survey results. We present an updated Galactic model implementation within the \synthpop framework that has been tuned for simulating the upcoming Nancy Grace Roman Space Telescope's Galactic Bulge Time Domain Survey (RGBTDS). We evaluate the model against stellar catalogs and kinematics from optical and infrared surveys toward the Galactic bulge, finding good agreement in much of the bulge, including the RGBTDS' contiguous lower bulge fields. However, within Galactic latitudes of $b\lesssim0.5^\circ$ of the Galactic plane, some inconsistencies arise which may impact projections for the RGBTDS' Galactic center field. In a following paper, we will examine RGBTDS simulations with this updated model in detail. Roman's GBTDS and Galactic Plane Survey will be instrumental in resolving the remaining model inconsistencies and improving our understanding of the structure of the central few degrees of our Galaxy.

An Updated \synthpop Model for Microlensing Simulations I: Model Description, Evaluation, and Microlensing Event Rates Near the Galactic Center

Abstract

The optimization and interpretation of microlensing surveys depends on having an accurate model of the Milky Way. However, existing Galactic modeling tools often perform poorly in replicating the stellar contents of the inner Galactic bulge region and reproducing microlensing survey results. We present an updated Galactic model implementation within the \synthpop framework that has been tuned for simulating the upcoming Nancy Grace Roman Space Telescope's Galactic Bulge Time Domain Survey (RGBTDS). We evaluate the model against stellar catalogs and kinematics from optical and infrared surveys toward the Galactic bulge, finding good agreement in much of the bulge, including the RGBTDS' contiguous lower bulge fields. However, within Galactic latitudes of of the Galactic plane, some inconsistencies arise which may impact projections for the RGBTDS' Galactic center field. In a following paper, we will examine RGBTDS simulations with this updated model in detail. Roman's GBTDS and Galactic Plane Survey will be instrumental in resolving the remaining model inconsistencies and improving our understanding of the structure of the central few degrees of our Galaxy.
Paper Structure (25 sections, 6 equations, 16 figures)

This paper contains 25 sections, 6 equations, 16 figures.

Table of Contents

  1. Introduction
  2. Model Description
  3. Stellar Densities & Kinematics
  4. Stellar Properties and Evolution
  5. Extinction
  6. Preliminary SP-H24 Model
  7. Luminosity, Color, and Star Count Evaluations
  8. The WFC3 Galactic Bulge Treasury Program
  9. Optical Gravitational Lensing Experiment
  10. VISTA Variables in the Via Lactea
  11. Nuclear Stellar Disk
  12. Kinematic Model Evaluations
  13. The WFC3 Galactic Bulge Treasury Program
  14. Gaia Proper Motions
  15. Nuclear Stellar Disk Proper Motions
  16. ...and 10 more sections

Figures (16)

  • Figure 1: Observed and simulated luminosity functions for the WFC3 Galactic Bulge Treasury Program Brown2009Brown2010 fields in STMAG Koornneef1986.
  • Figure 2: Observed Terry2020 and simulated bulge-only luminosity functions for the Stanek Window ($l=0.25^\circ$, $b=-2.15^\circ$). Magnitudes are shown in the VEGAMAG system.
  • Figure 3: Comparison of OGLE EWS color-magnitude diagrams for four sample event alerts within the region of sky covered by our extinction map, with OGLE EWS data in black and SP-H25 in blue on the left two columns. The third and fourth columns show histograms of I magnitude and V-I color, respectively.
  • Figure 4: Star count ratio maps for I$<$18 (left), I$<$21 (right), comparing OGLE-IV results from Mroz2019 and SP-H25 model generated catalogs, limiting to the OGLE chips covered by the Surot2020 extinction map.
  • Figure 5: Color-magnitude diagrams and luminosity functions for VIRAC2 stars and the SP-H25 model.
  • ...and 11 more figures