Extragalactic Microlensing: Quasars, Caustics & Dark Matter

Transcription

1 Extragalactic Microlensing: Quasars, Caustics & Dark Matter Joachim Wambsganss Universität Heidelberg April 22, 2009 JENAM / NAM University of Hertfordshire

2 Extragalactic Microlensing: Quasars, Caustics & Dark Matter History of the other microlensing Refsdal, Refsdal, Paczyński, Refsdal, et al., Basics of quasar microlensing mass scales, distance scales, angular scales Usefulness of quasar microlensing quasar structure, transverse velocity, dark matter Future of quasar microlensing sharper, better, more

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4 260 citations 150 citations 4

5 1981 Gott: "Are heavy halos made of low mass stars? A gravitational lens test" (correcting Einstein: a distant stellar microlensing IS observable...)»extragalactic Microlensing: Quasars, Quasars, Caustics Caustics and and Dark Dark Matter«Matter«Joachim Joachim Wambsganss (Universität (Universität Heidelberg), Heidelberg), Invited Invited talk talk at at Symposium Symposium Gravitational Lenses, Lenses, JENAM, JENAM, Univ. Univ. of of Hertfordshire, April April 22, 22,

6 1986 Paczyński:»Extragalactic Microlensing: Quasars, Caustics and and Dark Dark Matter«Invited talk at Univ. of April 22,

7 1989 Irwin et al.: "Photometric variations in the Q system - First detection of a microlensing event" Two decades of quasar microlensing... 7

8 Extragalactic Microlensing: Quasars, Caustics & Dark Matter History of the other microlensing Refsdal, Refsdal, Paczyński, Refsdal, et al., Basics of quasar microlensing mass scales, distance scales, angular scales Usefulness of quasar microlensing quasar structure, transverse velocity, dark matter Future of quasar microlensing sharper, better, more

9 Basics of Lensing: Geometry He burned his house down for the fire insurance and spent the proceeds on a telescope... Robert Frost: "The Star-Splitter" 9

10 Quasar microlensing: Basics Einstein radius: θ E 1.8 M M microarcsec Einstein time: t E = r E /v 15 M M v years Crossing time: (for z L = 0.5, z S = 2.0) 10

11 How can we observe micro-lensing? Einstein angle (θe = 2 (M/M ) microarcsec) << telescope resolution! image splitting not directly observable! However, microlensing affects: apparent magnitude (magnification) (emission/absorption line shape) center-of-light position These effects change with time due to relative motion of source, lens and observer: microlensing is a dynamic phenomenon! It is observable: photometrically (spectroscopically) astrometrically

12 a a a a a Two regimes of microlensing: compact objects in the Milky Way, or its halo, or the local group acting on stars in the Bulge/LMC/SMC/M31: a a stellar microlensing a Galactic microlensing a local group microlensing a optical depth: ~10-6 compact objects in a distant galaxy, or its halo acting on even more distant (multiple) quasars quasar microlensing extragalactic microlensing cosmological microlensing a optical depth: ~1 near far

13 Two Regimes of Gravitational Microlensing: main lenses: stellar, Galactic, Local Group microlensing stellar mass objects in Milky Way, SMC, LMC, M31, halo quasar, extragalactic, cosmological microlensing stellar mass objects in lensing galaxy sources: kpc/mpc quasars Gpc Einstein angle: 0.5 milliarcsec 1 microarcsec Einstein time: weeks-months months-years optical depth: low: 10-6 high: of order 1 proposed: (Einstein 1936) Paczynski 1986a Chang & Refsdal 1979, 1984 Gott 1981, Paczynski 1986b first detected: OGLE, MACHO, EROS 1993 Irwin et al way of detection: photometrically, spectroscopically, astrometrically photometrically, spectroscopically, astrometrically signal: simple complicated good for: machos, stars, planets, (moons?) stellar masses/profiles, structure quasar sizes/profiles, machos, dark matter

14 Quasar microlensing: typical magnification patterns L = 100 R E 20 R E 0.8 R E 4 R E

15 Quasar Microlensing 15

16 Extragalactic Microlensing: Quasars, Caustics & Dark Matter History of the other microlensing Refsdal, Refsdal, Paczyński, Refsdal, et al., Basics of quasar microlensing mass scales, distance scales, angular scales Usefulness of quasar microlensing quasar structure, transverse velocity, dark matter Future of quasar microlensing sharper, better, more

17 Quasar microlensing: The Promises The current achievements Microlensing of quasars can be used to determine: Effects of compact objects along the line of sight Done! Size of quasar Yes! (Two-dimensional) brightness profile of quasar Sort of! Mass (and mass function) of lensing objects Some Limits! Detection of smoothly distributed (dark) matter Getting quantitative! 17

18 Quasar microlensing: typical simulations

19 Quasar Microlensing: Q Udalski et al (OGLE) many analyses: Kochanek et al. Yonehara et al. Wyieth et al

20 Accretion disk profile from quasar microlensing (see by Dominique Sluse; Eigenbrod et al. 2008) studying chromatic variations in the UV/optical continuum of quadruple quasar Q , images A and B, OGLE V-band data, fitted with different microlensing lightcurves spectroscopic data, reproduced as 6 filters : 39 epochs of spectrophotometric monitoring

21 Quasar Microlensing at high magnification: suppressed saddlepoints and the role of dark matter (Schechter & Wambsganss 2002) PG : 0.48", Δm = 0.5 mag (Weymann et al. 1980) SDSS : 0.66", Δm = 2.5 mag (Inada et al. 2003) 21

22 Quasar Microlensing at high magnification: suppressed saddlepoints and the role of dark matter (Schechter & Wambsganss 2002) MG : close pairs of bright images: should be about equal in brightness they are not! saddle point image demagnified! at least 4 similar systems what's going on?!? microlensing? substructure? DM? CASTLES 22

23 Quasar Microlensing at high magnification: suppressed saddlepoints and the role of dark matter (Schechter & Wambsganss 2002) κ tot = constant in horizontal rows κ smooth = 0% = 85% = 98% saddle point image: minimum image: 23

24 minimum: Quasar Microlensing at high magnification: suppressed saddlepoints and the role of dark matter (Schechter & Wambsganss 2002) κ tot = const in columns saddle: κ smooth = 0% = 85% = 98% 24

25 The Dark-Matter Fraction in the Elliptical Galaxy Lensing the Quasar PG Determination of most likely dark-matter fraction in elliptical galaxy lensing quasar PG : based on analyses of the X-ray fluxes of individual images in 2000 and 2008: Pooley, Rappaport, Blackburne, Schechter, Schwab, Wambsganss (arxiv: )

26 The Dark-Matter Fraction in the Elliptical Galaxy Lensing the Quasar PG Optical (green) and X-ray (red) flux ratio between images A1 and A2 vs. time: X-ray fluxes vs. time for individual images in PG : Pooley, Rappaport, Blackburne, Schechter, Schwab, Wambsganss (arxiv: )

27 The Dark-Matter Fraction in the Elliptical Galaxy Lensing the Quasar PG Microlensing magnification map for image A2 Pooley, Rappaport, Blackburne, Schechter, Schwab, Wambsganss (arxiv: )

28 The Dark-Matter Fraction in the Elliptical Galaxy Lensing the Quasar PG Pooley, Rappaport, Blackburne, Schechter, Schwab, Wambsganss (arxiv: )

29 Extragalactic Microlensing: Quasars, Caustics & Dark Matter History of the other microlensing Refsdal, Refsdal, Paczyński, Refsdal, et al., Basics of quasar microlensing mass scales, distance scales, angular scales Usefulness of quasar microlensing quasar structure, transverse velocity, dark matter Future of quasar microlensing sharper, better, more

30 Odd Images : Microlensing Magnification Maps forofpmn J Microlensing Central Lensed Images 3 (Winn et al. 2002, 2003, 2004) A B C Microlensing of Central Lensed Images Rsrc = 0.1 Rsrc = 1 9 Rsrc = C 0.1 C 0.4 C 0.2 B 0.1 B A!!! B 0.2 A A f = "stars/"tot f = "stars/"tot f = "stars/"tot Figure 8. Magnification dispersion as a function of the fractional surface density in stars, f = κstars /κtot, for three different source sizes (quoted in units of RE ). The errorbars indicate the statistical uncertainties estimated with bootstrap and jackknife resampling (e.g., Efron 1982). µa = 4.6 µb =0.4 Image fmax 500 A B C ± ± ± σ (in dex) 1 Rsrc = µc = Dobler, Keeton & Wambsganss (2007)! Figure 1. Sample magnification0.2 maps for images AC (left), B (center), and C (right). The maps are 50RE on a side, and the fraction Table 2. Column 2 gives our estimate of the upper limit on of surface mass density in stars is f = 100%. The colorbar at the bottom indicates number of rays in each pixel, which is directly /κtot (see text). The quoted the uncertainties are derived f = κstars B from the uncertainty in the power law index of the lens galaxy 0.1 proportional to the magnification. The number of rays corresponding to a magnification of unity is 25.8 for image A, 442 for B, and mass distribution (α = 0.91 ± 0.02; Winn et al. 2003). Columns 3 5 give upper limits on the magnification dispersion σ (in dex), 14, 200 for C. We use a logarithmic color mapping. A for three source sizes (quoted in units of R ). These upper limits 0.05 E!# 3 RESULTS Rsrc-1 10 Rsrc 3.1 Magnification maps Figure 7. Magnification dispersion as a function of source size, were obtained by combining fmax with the σ vs. f curves in Figure 8. The uncertainties in σ due to the uncertainties in fmax are " 0.05 dex. The dispersion can be extrapolated to larger source sizes with the scaling σ R 1 src (Refsdal & Stabell 1991, 1997). we define the auto-correlation function along linear slices through the maps (see Wambsganss et al. 1990a): than for other images, even when the source is fairly large (Rsrc /RE! 1). Our most intriguing qualitative result concerns the sensitivity of central image microlensing to the relative densities of stars and dark matter. When the2source is large (Rsrc /RE! 3), the magnification dispersion decreases monotonically with the fraction f of density in stars. How2 Matter«ever, when Caustics the source isand smalldark (Rsrc /R E»Extragalactic Microlensing: Quasars, E " 3), the magnifivlop more and more cusps and folds.invited For the talk demagnified cation dispersion rises as f Lenses, is decreased JENAM, from unity, reaches Wambsganss (Universität Heidelberg), at Symposium Gravitational Univ. saddle, low values of f yield cusps and folds, intermediate a peak at some finite value of f, and then falls to zero as values produce blobs, and at very large values 2(f 100%) f 0 (as it should in the absence of microlensing). This dee number of the cusps and folds reappear. Thus the relative pendence is similar to behavior seen by Schechter & Wambcusps and folds versus blobs has a complicated dependence sganss (2002) for a highly magnified saddle image. We do on κtot, γ, and f (see also Petters et al. 2001). not see such behavior for a demagnified saddle, but we do for the three images, assuming f = 100% of the mass in stars. The line segment below the curve for image A shows the expected asymptotic scaling for large sources, σ R 1 src (Refsdal & Stabell 1991, 1997). Figure 1 shows magnification maps for f = 100% of the surface density in stars, with the caveat that to make the features visible we only show (50R ) maps here. The map Joachim for image C in particular shows that there is structure on scales of tens of Einstein radii, so even a (100R ) map does not contain a fully representative sample of magnifications.!µ(x)µ(x + x)"!µ(x)"2, ξ( x) =!µ(x) "!µ(x)"2 (3) where µ(x) is the magnification at position x and the averof Hertfordshire, April 22, 2009 ages are over all positions along the slide. For each map, we calculate ξ( x) for each row and average over rows. We then further average over 50 maps (i.e., 50 random stellar configu-

31 Astrometric microlensing of quasars (Treyer & Wambsganss 2004)

32 Astrometric microlensing of quasars: (Treyer & Wambsganss 2004) 32

33 Animated astrometric microlensing of quasars (Treyer & Wambsganss 2004) 33

34 Quasar microlensing: The Promises The current achievements Microlensing of quasars can be used to determine: Effects of compact objects along the line of sight Done! Size of quasar Yes! (Two-dimensional) brightness profile of quasar Sort of! Mass (and mass function) of lensing objects Some Limits! Detection of smoothly distributed (dark) matter Getting quantitative! 34

35 More Quasar Microlensing to come... : Microlensing Talks: Dominique Sluse: Microlensing as a Tool to Probe the Quasar Structure Timo Anguita: COSMOS : a New Strong Gravitational Lensing System Microlensing Poster: Nick Bate: Constraining Accretion Discs in Anomalous Lensed Quasars Dana Paraficz: Results of Optical Monitoring of 5 SDSS Double QSOs with the Nordic Optical Telescope

36 The future of quasar microlensing for determining the surface brightness profiles of quasars as a function of wavelength for measuring masses of lensing objects for evaluating the dark matter content of lensing galaxies is very promising and dynamic! Quasar 20 years: coming of age! 36