The Origin of the Microlensing Events Observed Towards the LMC and the Stellar Counterpart of the Magellanic Stream

Abstract

We introduce a novel theoretical model to explain the long-standing puzzle of the nature of the microlensing events reported towards the Large Magellanic Cloud (LMC) by the MACHO and OGLE collaborations. We propose that a population of tidally stripped stars from the Small Magellanic Cloud (SMC) located ~4-10 kpc behind a lensing population of LMC disk stars can naturally explain the observed event durations (17-71 days), event frequencies and spatial distribution of the reported events. Differences in the event frequencies reported by the OGLE (~0.33 /yr) and MACHO (~1.75 /yr) surveys appear to be naturally accounted for by their different detection efficiencies and sensitivity to faint sources. The presented models of the Magellanic System were constructed without prior consideration of the microlensing implications. These results favor a scenario for the interaction history of the Magellanic Clouds, wherein the Clouds are on their first infall towards the Milky Way and the SMC has recently collided with the LMC 100-300 Myr ago, leading to a large number of faint sources distributed non-uniformly behind the LMC disk. In contrast to self-lensing models, microlensing events are also expected to occur in fields off the LMC's stellar bar since the stellar debris is not expected to be concentrated in the bar region. This scenario leads to a number of observational tests: the sources are low-metallicity SMC stars, they exhibit high velocities relative to LMC disk stars that may be detectable via proper motion studies, and, most notably, there should exist a stellar counterpart to the gaseous Magellanic Stream and Bridge with a V-band surface brightness of > 32 mag/arcsec^2. In particular, the stellar Bridge should contain enough RR Lyrae stars to be detected by the ongoing OGLE survey of this region.

Accepted for publication in MNRAS, 28 pages, 18 figures

References in corpus (13)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• Limits on the Macho Content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds
• Are the Magellanic Clouds on their First Passage about the Milky Way?
• Is the SMC Bound to the LMC? The HST Proper Motion of the SMC
• The Origin of the Magellanic Stream and Its Leading Arm
• Exploring Halo Substructure with Giant Stars XI: The Tidal Tails of the Carina Dwarf Spheroidal and the Discovery of Magellanic Cloud Stars in the Carina Foreground
• New Optical Reddening Maps of the Large and Small Magellanic Clouds
• The Magellanic Bridge: The Nearest Purely Tidal Stellar Population
• Dynamics of the Magellanic Clouds in a LCDM Universe
• Three dimensional maps of the Magellanic Clouds using RR Lyrae Stars and Cepheids II. The Small Magellanic Cloud
• Implications of Recent Measurements of the Milky Way Rotation for the Orbit of the Large Magellanic Cloud
• Microlensing as a probe of the Galactic structure; 20 years of microlensing optical depth studies
• Constraints on the Magellanic Clouds' Interaction from the Distribution of OB Stars and the Kinematics of Giants

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