Possible Implications of Sagittarius Type Dwarf Galaxy on Microlensing Towards the Large Magellanic Cloud

Abstract

The discovery of the Sgr dwarf galaxy (Ibata, Gilmore, Irwin 1994) shows that the Galactic halo contains large clumps which are not full viralized. Stars in such a clump can lense a background extragalactic source. I use parameters of Sgr to demonstrate that microlensing by a disintegrated dwarf galaxy has a probability (optical depth) $10^{-7}-10^{-6}$, which is comparable to that of an isothermal Galactic dark halo of massive compact objects (MACHOs). This may change implications of observed microlensing events towards the LMC. If more than one such clumps are hidden in the Galactic halo, then given their enormous angular size ($\sim 5^o \times 20^o$), there is a significant chance for {\sl any} line of sight, say the LMC direction, to intersect one of them. As an alternative to the half-MACHO dark halo models (Alcock et al. 1996a,c), I discuss a non-MACHO model with lenses of the observed events being faint stars in a hidden Sgr-like disintegrated dwarf in the line-of-sight path to the LMC.