Color Anomaly in Multiple Quasars - Dust Inhomogeneity or Quasar Microlensing - Atsunori Yonehara (Univ. Tsukuba) with Hiroyuki Hirashita (Nagoya Univ.) Philip Richter (Arcetri Obs. ?) in progress

Topics 1. Multiple Quasars 2. Observed Color Anomaly 3. Inhomogeneity in Lens Galaxy 4. Quasar Microlensing 5. Discussion

1. Multiple Quasars What is multiple quasars ? Gravitationally lensed quasars with multiple (generally, 2 or 4) images. Gravitationally lensed quasars with multiple (generally, 2 or 4) images. Lens object is a foreground galaxy (some system has no apparent lens object or nearby cluster contribution). Lens object is a foreground galaxy (some system has no apparent lens object or nearby cluster contribution). How many ? A several tenth of such objects have been detected. The number is still increasing thanks to many surveys. They are rear, but useful astrophysical tools.

Samples of multiple quasars Q0957Q2237 RXJ0911 B1938 H1413B1359

Properties Image separation : ～ 1 (arcsec) ～ 1 (kpc) at z l ≒ typical lens size for singular isothermal sphere with σ ～ 200km/s Lensed images are nicely fitted by a point source. Corresponding images show similar spectral features. Source redshift Lens redshift source observer lens image A image B

2. Observed Color Anomaly In principle, gravitational lens phenomenon should have no wavelength dependence. ⇒ Images created from the same quasar should be observed with an identical color. ⇒ Images created from the same quasar should be observed with an identical color. However, not all but large number of multiple quasars show color anomaly. ⇒ 16/23 lens galaxies show median differential extinction with ΔE(B-V) ～ (Falco et al. 1999) … non-zero differential extinction (?)

Results in Falco et al.’s paper Falco et al. (1999) have summarized color anomaly in lens galaxy (CASTLEs survey). ← Reference: bluest image error: 0.01[mag.] (min.) observed B- & V- mag. ↓ non-negligible color anomaly exists in many systems. … patchy nature of gas/dust ? Number of images ΔE(B-V) [mag.] σ ＝ 0.01 Gaussian σ ＝ 0.1 Gaussian They only consider 2 colors.

ΔE A - ΔE B diagram Differential extinction - differential extinction diagram from CASTLEs Web page.  Sample selection: z l and z s are measured z l and z s are measured 3 photometric data are available (F160W, F555W, and F814W filter of HST) 3 photometric data are available (F160W, F555W, and F814W filter of HST) total: 15 objects total: 15 objects ↑ different from Falco et al. (1999)’s sample. ↑ different from Falco et al. (1999)’s sample.

Possible explanations This may due to the intervening lens galaxy. 1. Some inhomogeneity in lens galaxy Gas-to-dust ratio Ingredients of dust Column density of ISM 2. Quasar microlensing Optical depth for quasar microlensing is order of unity for all multiple quasars. SADM microlensing will show color change.

3. Inhomogeneity in Lens Galaxy Even if all galaxy has the same extinction properties as Milky Way, inhomogeneity of the (gas) density (e.g., spiral arms) may produce observed, differential extinctions. By using Hirashita et al. (2003)’s results, we randomly select locations in a galaxy and obtain gas density at the positions. ⇒ calculate extinctions and compare their value

ΔE A - ΔE B for inhomogeneity Two differential extinction show positive correlation. No negative ΔE B. Extinction curve for various n(H) (R V =3.1) ← Cardelli et al. (1989) ΔE A -ΔE B diagram

4. Quasar Microlensing When a stellar object in lens galaxy passes in front of an image, microlensing will occur. If matter in the lens galaxy consist only from stellar objects, optical depth for quasar microlensing can be order of unity. Einstein ring radius is comparable to the size of accretion disk in quasars, and finite size source effect is important for the quasar microlensing. ⇒ “color change”

Explanation for color change If one of multiple image suffers microlensing, color of the image will change. In general, all image can always be suffer quasar microlensing, independently. Extended source Compact source Lens Object time Flux Lens Object time Flux Different color !

Magnification pattern

An example of color change Randomly pick up epochs from this light curve and compare colors at different epochs. ⇒ “differential extinction”-like ← Light curve for quasar microlensing. z s =2.0, z l =1.0 M BH =10 8 M ◎ mass acc. rate ～ critical value typical caustic size Event time scale ～ a several [yr]

ΔE A - ΔE B for microlensing No apparent correlation between two differential extinctions. Both of positive and negative ΔE B exist. (Average magnification, μ ave, for both image = 10. (Average magnification, μ ave, for both image = 10. μ tot =μ ave +μ qml (t) ) μ tot =μ ave +μ qml (t) ) ΔE A -ΔE B diagram

5. Discussion Except some special case, negative correlations between two differential extinction cannot be produced in the case of inhomogeneity in lens galaxies. For positive correlation part, differential extinction can be explained by patchy extinction properties (more things to do). However, quasar microlensing can easily reproduce observed color anomaly.

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