Microlensing of tidal debris on the Magellanic great circle

Abstract

Increasing evidences suggest that the Galactic halo is lumpy on kpc scales due to the accretion of at least a dozen small galaxies (LMC/SMC, Sgr, Fornax etc.). Faint stars in such lumpy structures can significant microlense a background star with an optical depth $10^{-7}-10^{-6}$, which is comparable to the observed value to the LMC (Alcock et al. 1996c). The observed several microlensing events towards the LMC can be explained by a tidal debris tail lying in the Magellanic plane if the progenitor of the Magellanic Clouds and Stream and other satellite galaxies in the Magellanic plane has a mass about twice that of the disc of the LMC. The LMC stars can either lense stars in the debris tail behind the LMC, or be lensed by stars in the part of debris tail in front of the LMC. The models are consistent with an elementary particle dominated Galactic halo without massive compact halo objects (MACHOs). They also differ from Sahu's (1994) LMC-self-lensing model by predicting a higher optical depth and event rate and less concentration of events to the LMC center.