Gravitational Lensing 6 Extragalactic Microlensing Local Group vs

Gravitational Lensing - 6 Extragalactic Microlensing

Local Group vs. Extragalactic Microlensing =k /2, 3 -pt lens /sharp caustic crossing Wambsganss 2001

Local Group vs. Extragalactic Microlensing Local Group Microlensing – very low optical depth Light curves of individual events These are fit with analytic models with 5 -10 parameters Derived quantity: Microlensing event is reproduced exactly (modulo some degeneracies) Extragalactic Microlensing – optical depth of order 1 Light curves cannot be separated into events due to individual stars These are not fit, but compared, in a statistical sense, in terms of amplitude of fluctuations to light curves extracted from magnification patterns Derived quantity: Probability that the fluctuations of the observed light curve are similar in amplitude to those of simulated ones obtained from the magnification patterns

Microlensing by stars in external galaxies caustic/magnification pattern tra ns ve rse hang a large, few 1000 AU, screen at the location of the Solar System mo tio no f. Q SO /g a lax y light passes through galaxies which consists of DM and stars one of the QSO macro-images

Magnification Patterns Schechter & Wambsganss 2002

Microlensing movie Microlensing of one of the macro images of a quad Q 2237+0305. Lens: spiral at zl=0. 0394. Source: QSO at zs=1. 69. From macro model of lens: convergence=0. 4 shear=0. 4 Stars (microlenses): Salpeter MF, M=0. 01 0. 5 M 0 velocity dispersion = 100 km/s Screen at observer: 2000 AU Elapsed time = 200 years

Microlensing – Q 2237+231 lens: barred spiral at z=0. 0394 source: QSO at z=1. 695 Image light curves 1 arcsec ~ 1 kpc at the redshift of galaxy flux changes are due to microlensing by stars in the lensing galaxy size of quasar’s optically emitting accretion disk < Einstein ring of a typical star in the lensing galaxy can study accretion disk structure using multi-wavelength flux ration of quasar images

Demagnification of saddle images saddles minima |magnif|=10 Schechter & Wambsganss 2002

Micro images making up macro images A macro minimum has to have a micro-minimum among its micro images cannot be demagnified. Macro minima are more often than not brighter than saddles in a close image pair Saha & LLRW 2011 If stars are present in the lensing galaxy, macro images are split into micro images

Micro images making up macro images A macro saddle does not need to have a micro-minimum among its micro images demagnification of saddles. Macro saddles can be fainter than neighboring minimum in a close image pair: Saha & LLRW 2011 If stars are present in the lensing galaxy, macro images are split into micro images

Micro images making up macro images A macro saddle does not need to have a micro-minimum among its micro images demagnification of saddles. Macro saddles can be fainter than neighboring minimum in a close image pair: Saha & LLRW 2011 If stars are present in the lensing galaxy, macro images are split into micro images

Demagnification of saddles macro minima; m=+5 histograms: 0, 1, 2, 3, 4 micro min. Saha & LLRW 2010 histograms: 1, 2, 3, 4 micro min. macro saddles; m=-5 If micro- or milli-lensing is the correct interpretation of the flux anomalies, then would expect saddles to be preferentially fainter than minima, as is observed.