PROBING 100 AU INTERGALACTIC Mg ii ABSORBING ‘‘CLOUDLETS’’ WITH QUASAR MICROLENSING

Intergalactic Mg ii absorbers are known to have structures down to scales 10 pc, and there are now indications that they may be fragmented on scalesP10 2.5 pc according to Hao and coworkers. When a lensed quasar is microlensed, the microimages of the quasar experience creation, destruction, distortion, and drastic astrometric changes during caustic crossings. I show that quasar microlensing can effectively probe Mg ii and other absorption ‘‘cloudlets’’ with sizes 10 4.0 to 10 2.0 pc by inducing significant spectral variability on timescales of months to years. With numerical simulations, I demonstrate the feasibility of applying this method to Q2237+0305, and I show that highresolution spectra of this quasar in the near futurewould provide a clear test of the existence of suchmetal-line absorbing ‘‘cloudlets.’’ Subject headinggs: gravitational lensing — intergalactic medium — quasars: absorption lines