Are the Ogle Microlenses in the Galactic Bar?

Abstract

The analysis of the first two years of OGLE data revealed 9 microlensing events of the galactic bulge stars, with the characteristic time scales in the range $8.6<t_0<62$ days, where $t_0=R_E/V$. The optical depth to microlensing is larger than $(3.3\pm 1.2)\times 10^{-6}$, in excess of current theoretical estimates, indicating a much higher efficiency for microlensing by either bulge or disk lenses. We argue that the lenses are likely to be ordinary stars in the galactic bar, which has its long axis elongated towards us. A relation between $t_0$ and the lens masses remains unknown until a quantitative model of bar microlensing becomes available. At this time we have no evidence that the OGLE events are related to dark matter. The geometry of lens distribution can be determined observationally when the microlensing rate is measured over a larger range of galactic longitudes, like $-10^o<l<+10^o$, and the relative proper motions of the galactic bulge (bar) stars are measured with the HST.

10 pages, 2 figures, revised version accepted for the publication in ApJL, uses AAS LaTeX aaspp.sty macro, PostScript figures and PostScript version of the paper available through anonymous ftp from astro.princeton.edu, directory stanek/tau, or on request

Cited by in corpus (52)

• Wide-Field InfrarRed Survey Telescope-Astrophysics Focused Telescope Assets WFIRST-AFTA 2015 Report
• Gravitational Microlensing in the Local Group
• COBE's Galactic Bar and Disk
• Spiral arms, bar shape and bulge microlensing in the Milky Way
• Gas Dynamics and Large-Scale Morphology of the Milky Way Galaxy
• Modelling the Galactic Bar Using Red Clump Giants
• Microlensing optical depth towards the Galactic bulge from MOA observations during 2000 with Difference Image Analysis
• The Nature of Boxy/Peanut-Shaped Bulges in Spiral Galaxies
• Order and chaos in the local disc stellar kinematics induced by the Galactic bar
• First Observation of Parallax in a Gravitational Microlensing Event
• The MACHO Project: 45 Candidate Microlensing Events from the First Year Galactic Bulge Data
• Galactic Bulges
• The MACHO project: Microlensing Optical Depth towards the Galactic Bulge from Difference Image Analysis
• Separation of Stellar Populations by an Evolving Bar: Implications for the Bulge of the Milky Way
• The 1995 Pilot Campaign of PLANET: Searching for Microlensing Anomalies through Precise, Rapid, Round-the-Clock Monitoring
• Bar Diagnostics in Edge-On Spiral Galaxies. II. Hydrodynamical Simulations
• Microlensing optical depth toward the Galactic Bulge using bright sources from OGLE-II
• Microlensing optical depth and event rate toward the Galactic bulge from 8 yr of OGLE-IV observations
• The Microlensing Event Rate and Optical Depth Toward the Galactic Bulge from MOA-II
• OGLE-III Microlensing Events and the Structure of the Galactic Bulge
• Results from a Survey of Gravitational Microlensing towards M31
• A Dynamical Model of the Inner Galaxy
• The Pattern Speed of the OH/IR Stars in the Milky Way
• The Properties of Long-Period Variables in the Large Magellanic Cloud from MACHO
• Long Period Variables in the LMC: Results from MACHO and 2MASS
• Variable Evolved Stars and YSOs Discovered in the Large Magellanic Cloud using the SAGE Survey
• Microlensing
• The LMC Microlensing Events: Evidence for a Warped and Flaring Milky Way Disk?
• Microlensing constraints on the Galactic Bulge Initial Mass Function
• Limits on the microlens mass function of Q2237+0305
• New insights on the Galactic Bulge Initial Mass Function
• WeCAPP - The Wendelstein Calar Alto Pixellensing Project I Tracing Dark and Bright Matter in M31
• A major star formation region in the receding tip of the stellar Galactic bar. II. Supplementary information and evidence that the bar is not the same structure as the triaxial bulge previouly reported
• Possible Solution of the long-standing discrepancy in the Microlensing Optical Depth Toward the Galactic Bulge by correcting the stellar number count
• A Schwarzschild model of the Galactic bar with initial density from N-body simulations
• SiO Maser Survey of the Inner Bar of the Galactic Bulge
• On Microlensing Event Rates and Optical Depth toward the Galactic Center
• The Maximum Optical Depth Towards Bulge Stars From Axisymmetric Models of the Milky Way
• The long bar as seen by the VVV Survey: II. Star counts
• Bright Lenses and Optical Depth
• The Sagittarius dwarf galaxy as a microlensing target
• Studying the Galactic Bulge Through Spectroscopy of Microlensed Sources: I. Theoretical Considerations
• Signatures of the Galactic bar on stellar kinematics unveiled by APOGEE
• Flattened Galactic Haloes and Baryonic Dark Matter
• Microlensing of disk sources
• Microlensing of Globular Clusters as a Probe of Galactic Structure
• Microlensing Optical Depth Revisited with Recent Star Counts
• Models of Bars with Exponential Density Profiles
• The Galactic Bar
• Studying the Galactic Bulge Through Spectroscopy of Microlensed Sources: II. Observations
• Gravitational Microlensing, The Distance Scale, And The Ages
• Bar Properties and Star-by-Star Bar Membership via Action Conservation