6 Extragalactic Microlensing Wambsganss 2001 sharp caustic crossing 23pt lens Local Group vs Extragalactic Microlensing k Local Group Microlensing very very low optical depth ID: 799180
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Slide1
Gravitational Lensing - 6
Extragalactic Microlensing
Slide2Wambsganss
2001
/sharp caustic crossing
/2,3-pt lens
Local Group vs. Extragalactic Microlensing
=k
Slide3Local Group Microlensing –
very very low optical depth
L
ight 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 starsThese are not fit, but compared, in a statistical sense,
in terms of amplitude of fluctuations to light curves extracted from magnification patternsDerived quantity: Probability that the fluctuations of the observed light curve are similar in amplitude to those of simulated ones obtained from the magnification patterns
Local Group vs. Extragalactic Microlensing
Slide4Microlensing by stars in external galaxies
hang a
large,
few 1
000
AU,
screen at the
location of the
Solar System
one of the QSO
macro-
images
light passes
through galaxies
which consists
of DM and
stars
transverse motion of
QSO/galaxy
caustic/magnification pattern
Slide5Magnification Patterns
Schechter &
Wambsganss
2002
Slide6Microlensing movie
Microlensing of one of the
macro images of a quad
Q2237+0305.
Lens: spiral at
zl=0.0394.Source: QSO at zs=1.69.From macro model of lens:
convergence=0.4 shear=0.4Stars (microlenses): Salpeter MF, M=0.010.5 M0
velocity dispersion = 100 km/s
Screen at observer: 2000
AU
Elapsed time = 200 years
Slide7Microlensing – Q2237+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
Slide8Demagnification of saddle images
minima
saddles
|
magnif
|=10
Schechter &
Wambsganss
2002
Slide9Micro images making up macro images
If stars are
present
in the
lensing galaxy,macro images are
split into micro images
A macro minimum
has to have amicro-minimumamong itsmicro images cannot bedemagnified.Macro minimaare more often
than not brighter
than saddles in a
close image pair
Saha & LLRW 2011
Slide10Micro images making up macro images
If stars are
present
in the
lensing galaxy,macro images are
split into micro images
A macro saddle
does not need to have a micro-minimumamong itsmicro images demagnificationof saddles.Macro saddlescan be fainter
than neighboring
minimum in a
close image pair:
Saha & LLRW 2011
Slide11Micro images making up macro images
If stars are
present
in the
lensing galaxy,macro images are
split into micro images
A macro saddle
does not need to have a micro-minimumamong itsmicro images demagnificationof saddles.Macro saddlescan be fainter
than neighboring
minimum in a
close image pair:
Saha & LLRW 2011
Slide12Demagnification of saddles
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.
macro minima;
m=+5 macro saddles; m=-5histograms: 1,2,3,4 micro min. histograms:
0,1,2,3,4 micro min.
Saha & LLRW 2010