Atsunori Yonehara (Univ. Tsukuba, JSPS Fellow)

with Hiroyuki Hirashita & Phillip Richter

Lines of my talk

1. Lensed Quasars with Multiple Images - general introductions -

2. Chromaticity and the Possible Origins - prologue -

3. Absorption Properties of Lens Galaxies - scenario 1 -

4. Quasar Microlensing - scenario 2 -

5. Discussions - epilogue -

1. Lensed Quasars with

Multiple Images

” ” What kind of objects ? ” What kind of objects ? ”

1.1 Multiple QuasarsWhat are “ lensed quasars with multiple images ” ?

The lens object is a foreground galaxy, i.e., a galaxy in the vicinity of line-of-sight to quasars (sometimes, effects of clusters should be taken into account)Path of photons from quasars is gravitationally lensedMultiple images ( “mirages” ) of the quasars are created and the number is 2 or 4 in usual cases

source(quasar)

observer

lens galaxy

image A

image B

1.2 Current StatusHow to identify ?

1.1.Look for a quasar pair with small separation Look for a quasar pair with small separation 2.2.Measure their redshifts from spectroscopic studyMeasure their redshifts from spectroscopic study3.3.IFIF their redshifts are identical, they can be pair images of “ a lens their redshifts are identical, they can be pair images of “ a lens

ed quasar with multiple images ” !ed quasar with multiple images ” !How general ?

Of course, it is a rare phenomenonNow, more than 70 objects are knownThe number is still increasing thanks to many large surveys

Q0957 Q2237 B1938

1.3 Observational Properties

Redshift Distributionssource redshift : 1 - 3lens redshift : < 1

(unknown for some systems)

Observed Imagesnicely fitted by a point source

Image Separationstypically, 1[arcsec]

->> 1-10[kpc] @ lens redshift this corresponds to typical lens size

for singular isothermal sphere density profile with =200[km/s]

Magnificationsbelieved to be 10-100 times in total via lens modelingmagnification ratio between images have large variety

no lenssystemhere

2. Chromaticity and

the Possible Origins

” ” What is the problem? ” What is the problem? ” ” ” What can we do? ” What can we do? ”

2.1 Against Achromaticity In principle, gravitational lensing phenomena show no wavelength dependence, i.e., “ achromatic ”. ->> multiple images of the same source (quasar) should have identical colors.

In real universe, it is not true.Falco et al. have summarized B-V color difference between

multiple images. They found significant color difference between images. -> chromatic feature appears !

Nu

mb

er o

f im

ages

ΔE(B-V) [mag.]

σ＝ 0.01 Gaussian(observational error)

σ＝ 0.1 Gaussian

Falco et al. (1999)

2.2 Photon’s Worry Before we observe, photon suffers from 2

problems. (excepts redshift)

source

lens galaxy

observer

[ problem 1 ]

Absorbers in galaxies are spatially inhomogeneous (e.g., density contrast).

->> Suffers different absorption, and chromatic.

[ problem 2 ]

Distribution of stellar objects in galaxies is not exactly the same at different location.

->> Suffers different microlensing, and chromatic.

2.3 Data AnalysisIntrinsic flux variation of quasars and the time delay between images are not take into account.

To reduce ambiguities (for further investigations), we only choose objects that the lens and the source redshift have measured.To probe the origin of suggested chromatic feature, we only choose objects that photometric data of HST’s F160W-, F555W-, and F814W- filter are available. ->> obtain 2 independent color from the 3 bands. ->> Total : 15 objectsReferring the bluest image in a system, we make “[color-difference]-[color-difference]” diagram. ->> Intrinsic color of quasars are extracted.

2.4 Faces of the Samples

from CASTLEs Web-page

2.5 Color Differences8 objects show double imagesThe rest are quadruple

The lens galaxy of 3 objects is late-type (red cross).The lens galaxy of the rest is early-type (blue cross).

The sample is different from that of Falco et al. (1999)re

dder

Try to explain this, and probe something interesting !

3. Absorption Propertiesof

Lens Galaxies

” ” Possible origin (1) ” Possible origin (1) ” ” ” Expected natures ” Expected natures ”

3.1 Justifications Effects of absorber in the lens galaxy are not negligible, at least, for objects with the late-type galaxy lens.

As Dr. Hirashita (may) have already mentioned, gas distribution is clumpy over galactic scale. ->> different image suffers different extinction ! (even if the RV-value is homogeneous)

Winn et al. (2002)

spiral arm on an image !

3.2 Toward Comparison Calculate probability distribution of n(H) differenceApply extinction curve by Cardelli et al. (1989)Assume typical Galactic value of RV (=3.1) and “ n(H) to E(B-V) conversion ” lawSet the lens redshift

F160W F555W F814W

3.3 Expected Behavior

Color difference is large in shorter wavelength (clear correlation)Negative color-difference at longer waveband does not exist

Even if we accept different extinction laws, e.g., change RV, this behavior will not alter (except some special situations).

thin line : 90 % regionthick line : 50 % region

large n(H)

4. Quasar Microlensing

” ” Possible origin (2) ” Possible origin (2) ” ” ” Expected natures ” Expected natures ”

4.1 Justifications From lens modeling, matter density of the lens galaxy on the images of lensed quasar is roughly critical density. ->> If large fraction of the matter is consists from stellar objects, microlensing should occur frequently !

Different images magnified different manner, because their stellar distribution is not exactly identical.

Extended source(longer waveband)

Compact source(shorter waveband)

Lens Object

time

Flux

Lens Object

time

Flux

Different color !image A

image B

timescale : several years

4.2 Toward ComparisonAssume “ Assume “ standard-type accretion disk standard-type accretion disk ” model as a central ” model as a central engine of quasars and apply approximate formulae for engine of quasars and apply approximate formulae for magnification of quasar microlensing, we can calculate magnification of quasar microlensing, we can calculate the expected flux variations at various wavebands. the expected flux variations at various wavebands.

parameters: • zs=2.0, zl=1.0• MBH=108M◎

•accretion rate = critical value

Randomly pick up the data points and compare these colors, we can mimic the effect of quasar microlensing.

4.3 Expected BehaviorCorrelation between 2 color-difference still exists, but negative color-difference can be reproduced !

Several parameters are unknown (including accretion disk model) ->> They will be constrained from this chromatic properties.

black hole mass, accretion rate, magnification pattern, total and stellar mass density of the lens galaxy

5. Discussions

” ” Summary ” Summary ” ” ” More things to say ” More things to say ”

5.1 Summary Chromaticity really exists in lensed quasars with multiple images (at least, in part). <<- Intervening object naturally produce such feature.In some cases, chromatic feature is not able to be explained by absorption properties of galaxies. ->> Quasar microlensing can also be the origin (partly).However, if we did not assume RV-value etc. and/or accept some special lens redshift and/or other extinction curves, we can manage to reproduce “ quasar microlens ” -like color change only from absorption.

This kind of study opening new window to absorption properties of inter stellar matter in OTHER galaxies and structures/physical parameters of quasars.

5.2 An Example of Case Study

For objects with a late-type lens galaxy, we have performed rough fitting for RV by eye.

Only from these simple study, we cannot say many things about difference between absorption properties of our galaxy and that of other galaxies. (Solar values seem to be pretty good)

5.3 My Worry – Perspective -

Some of the multiple images still have large photometric error (even in the HST data). <<- Comes from the reference selection. Sometimes the bluest images have large photometric errors. Intrinsic flux variation of quasars and the time delay ->> This must be the third candidate of the chromatic features (primal origin !? the most important !?).

Future/on-going (monitoring) observations will provide nice opportunities or answer to approach these issues.

Photon’s worry is my worry, and I have to overcome !

To study structure of galaxies and quasars … To become happy …

Fin.