Microlensing and Compact Objects in Galaxies

Transcription

1 Microlensing and Compact Objects in Galaxies Joachim Wambsganss Zentrum für Astronomie der Universität Heidelberg (ZAH) Applications of Gravitational Lensing KITP, Santa Barbara October 4,

2 Microlensing and Compact Objects in Galaxies What is microlensing? s mass scales, angular scales, time scales Why is microlensing relevant for astrophysics? s lens/source, qualitative/quantitative, light/dark, near/far, stellar/quasar How can we observe microlensing? s photometric, spectroscopic, astrometric microlensing Which are the interesting microlensing results? quasar microlensing: quasar size, compact (cold) dark matter stellar microlensing: (no) machos, star structure, cool dark matter What is the future of microlensing? s unique, useful, universal 2

3 What is Microlensing? Gravitational microlensing is the action of compact objects of small mass along the line of sight to distant sources what is small mass? 10-6 < M/M < 10 3 what is compact? (much) smaller than Einstein radius what are the distant sources? quasars, stars 3

4 What is Microlensing? Overall scale in gravitational lensing: Einstein radius 4GM D LS θ E = 4GM LS = θ E = c 2 D c 2 L D S L S θ E 1.8 4GM θ E = M θ E 1.8 θ E 1.8 M M c M 2 M M D LS microarcsec = D L D S Einstein radius for star in distant galaxy: microarcsec microarcsec Einstein radius for star in Milky Way: θ E 0.5 θ E 0.5 θ E 0.5 M M M M M milliarcsec milliarcsec milliarcsec at: Applications of Gravitational Lensing, KITP, MSanta Barbara, October 4,

5 Why is microlensing relevant for astrophysics? (background source: stars) 1936 Einstein: "Lens-like action of a star by the deviation of light in the gravitational field 1986 Paczynski: "Gravitational Lensing by the Galactic Halo" 1991 Mao & Paczynski: "Gravitational microlensing by double stars and planetary systems 1993 Alcock et al. (MACHO team): "Possible gravitational microlensing of a star in the Large Magellanic Cloud 1993 Aubourg et al. (EROS team): "Evidence for gravitational microlensing by dark objects in the Galactic halo 1993 Udalski et al. (OGLE team): "The optical gravitational lensing experiment. Discovery of the first candidate microlensing event in the direction of the Galactic Bulge halo 5

6 Why is microlensing relevant for astrophysics? (background source: quasars) 1979 Chang & Refsdal: "Flux variations of QSO A, B and image splitting by stars near the light path" 1981 Gott: "Are heavy halos made of low mass stars? A gravitational lens test" 1986 Paczynski: Gravitational microlensing at large optical depth 1986 Kayser et al.: Astrophysical applications of gravitational micro-lensing 1987 Schneider/Weiss: A gravitational lens origin for AGN-variability? Consequences of micro-lensing 1989 Irwin et al.: "Photometric variations in the Q system: first detection of a microlensing event'' 6

7 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 near compact objects in a distant galaxy, or its halo a acting on even more distant (multiple) quasars a a quasar microlensing a extragalactic microlensing a cosmological microlensing a optical depth: ~1 far 7

8 How can we observe θ E 1.8 microlensing microarcsec? Direct imaging? impossible: Einstein angle << telescope resolution; however: magnification, line shape, position change with time due to relative motion of source, lens and M observer: θ microlensing is a dynamic E 0.5 milliarcsec phenomenon! Observable: photometrically spectroscopically astrometrically M M M what are the relevant time scales? (z L = 0.5, z S = 2.0) Einstein time: Crossing time: t E = r E /v 15 M M v years 8

9 Quasar Microlensing L= 100 RE 20 RE 0.8 RE 4 RE (from Wambsganss, Paczynski, Schneider 1990) 9

10 Quasar Microlensing 10

11 Quasar microlensing: The current achievements Quasar variability due to microlensing reveals: Effects of compact objects along the line of sight YES! Size of quasar PARTLY! Two-dimensional brightness profile of quasar NOT AT ALL! Mass (and mass function) of lensing objects SOME LIMITS! Detection of smoothly distributed (dark) matter STRONG HINTS! 11

12 A few highlights: Quasar microlensing The current achievements Quadruple Q : source size, v transverse Double Q : limits on machos Flux anomaly: Microlensing can do it Odd images Size is everything 12

13 Source size effect in quasar microlensing: 13

14 The quadruple quasar Q z(quasar) = 1.695, z(galaxy) = image separation 1.7 arcsec (HST) 14

15 Quasar Microlensing: Q Wozniak et al (OGLE) OGLE Web page 15

16 Quasar Microlensing: Q Limits on transverse velocity of lensing galaxy Monitoring campaign: 6 months in 2000 GLITP - Gravitational Lens International Time Project 16

17 Quasar Microlensing: Q Limits on transverse velocity of lensing galaxy: Idea: "typical" distance between caustics due to effective transverse motion: typical time scale between maxima! 17

18 Quasar Microlensing: Q Gil-Merino, Wambsganss et al. (2005) 18

19 Quasar Microlensing: Q limits on V trans : M = 1 M : V trans, 90% 2160 km/sec V trans, 95% 2820 km/sec M = 0.1 M : V trans, 90% 630 km/sec V trans, 95% 872 km/sec Gil-Merino, Wambsganss et al. (2005) 19

20 Quasar Microlensing? Q Falco et al. (1998); Kundic et al. (1997); Colley, Turner et al. (2001) 20

21 Quasar Microlensing Simulation: Q M 10-3 M 10-5 M Wambsganss et al. (2000) 21

22 Quasar Microlensing Results: Q Halo of lensing galaxy cannot consist entirely of compact objects (MACHOs) in certain mass ranges (Wambsganss et al. 2000) More systems, longer baseline better constraints! 22

23 Quasar Microlensing: 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) 23

24 Quasar Microlensing: suppressed saddlepoints and the role of dark matter (Schechter & Wambsganss 2002) MG : close pairs of bright images: they should be "about" a equal in brightness they are not! saddle point image a demagnified! at least 4 similar systems what's going on?!? CASTLES ML, substructure, DM? 24

25 Quasar Microlensing: Suppressed saddlepoints and the role of dark matter (Schechter & Wambsganss 2002) κ tot = constant in rows κ smooth = 0% = 85% = 98% saddle point image: minimum image: 25

26 Quasar Microlensing: suppressed saddlepoints and the role of dark matter (Schechter & Wambsganss 2002) κ tot = const in columns minimum: saddle: κ smooth = 0% = 85% = 98% 26

27 Most anomalous lensed quasar : SDSS J D B A Dec arcsec Keeton et al. (2006): We have obtained somewhat more than two seasons of predictions: R-band monitoring images datac for & SDSS D brighten Our analysis procedures are described in detail in Kochanek et al. (2005), so we provide only a brief summary here. We Keeton et al. measure (2006) the flux & of Morgan each quasar et image al. (2006): irect ACS WFC (left) and dispersed ACS HRC (right) 5 00 relative ; 5 00 to a sample of reference stars each frame. We keep the images relative of SDSS J from the Hubble Space Telescope. The direct orth upmicrolensing and east to the left. can Clockwise explain from the the top, the flux quasar ratio components anomaly positions of the components fixed, using the HST astrometry stretch for given the lensed by ancomponents, inverse hyperbolic and derive sinethe to PSF highlight both bright and faint features. An approximate wavelength are labeled A, C, B, and D. The dispersed image is rotated by 7 ayed with a nonlinear themaccio, dispersed image Moore model to show and et al. the quasar effective (2006): flux wavelength for each epoch solution. by simultaneously [See the electronic edition of the Journal for a color version of the left panel of th fitting the lens and the reference stars. The PSF is modeled by 3 nested, elliptical Gaussian components. The substructure cannot explain the flux ratio anomaly ally resolved spectroscopy galaxy is included of eight in thequadruply model at a constant lensed flux which galaxy surface brightness distribution with a linear B-splin h the Space Telescope we determine Imaging by fitting Spectrograph all the data (STIS). as a function of the (e.g., Bolton et al. 2006). The relative wavelength was g galaxy flux and then adopting the galaxy flux that produces Fig. 3. SDSS R band light curves for images A D. tions were attempted Joachim theon best 2004 Wambsganss: fit tojune the complete 19, but Microlensing guide data set. starand Compact the ground Objects The data calibration in points Galaxies for image of ACS D are (Pavlovsky offset to improveet their al. visibility. 2004), at: Most Applications of our observations of Gravitational were obtained Lensing, at KITP, the queue- Santa Barbara, The curves October are derived 4, 2006 from a joint, high-order polynomial fit for 27 failed. We arranged to reobserve SDSS J C RA arcsec more variability microlensing! Image D Dec arcsec 1.35 image D factor too faint ; anomaly present in 1.3 continuum & broad emission line flux 1.25 variability detected microlensing! R BLR 0.4 R E Image D RA arcsec Fig. 2. Substructure models for the SDSS flux ratio anomaly. The left (right) panels show the regions where a pseudo-jaffe model with an Einstein radius of (0. 003) can remove the A/D flux ratio anomaly without significantly worsening the constraints on the quasar image positions or the Einstein ring. The main lens is modeled as a singular isothermal ellipsoid (SIE) and the pseudo-jaffe models are tidally truncated at 0. 1 (0. 06). The position stars of image contribute D is indicated with 15-20% a white point. of χsurface 2 contours are mass indicated density in the figure legends. flux ratios. We include this calculation as an illustration that substructure can lead to anomalies as extreme as are observed here. Morgan et al. (2006): 3. MICROLENSING 3.1. Monitoring Data and Microlensing shifted the wavelength scale of each spectrum to match

28 Odd Images : Microlensing Magnification Maps forofpmn J Microlensing Central Lensed Images (Winn et al. 2002, 2003, 2004) R = 0.1 src A B C C !! B 0.2 A f = "stars/"tot µb =0.4 µa = Figure 8. Magnification dispersion as a function of the fra (quoted in units of RE ). The errorbars indicate the statis Efron 1982) Dobler, Keeton & Wambsganss (2006) 500 µc = ! Figure 1. Sample magnification maps for images A (left), B (center), and C (right). The maps are 50RE on a side, and the frac of surface mass density in stars is f = 100%. The colorbar at the bottom indicates the number of rays in each pixel, which is dire proportional to the magnification. The number of rays corresponding to a magnification of unity is 25.8 for image A, 442 for B, 0.2 C 14, 200 for C. We use a logarithmic color mapping RESULTS Magnification maps B 0.1 we define the auto-correlation function along linear sl A through the maps (see 0.05 Wambsganss et al. 1990a): -1! # Rsrc!µ(x)µ(x + x)"!µ(x)"2 Figure 1 shows magnification maps for f = 100% of the, ξ( x) = 2" !µ(x)!µ(x)" surface density in stars, with the caveat that to make the Wambsganss: Microlensing Objects in Galaxies features visible we Joachim only show (50RE )2 maps here. The and mapcompact Rsrc where µ(x) is the magnification at position x and the 28 a Applications of Gravitational for image C inat: particular shows that there islensing, structurekitp, on Santa Barbara, October 4, 2006

29 parison. Note er ( positive) is a central bolometric rank et al. ciency for rate Ṁ ¼ ation with :5M ¼ 3 ; the typical the formu- 2), we can An innerto a black er mass of of ¼ 0:2 ture-radius ion (3), we where G is Newton s constant and is the Stefan-Boltzmann constant. Using the values listed above for M, Ṁ, and r in, the maximum temperature is T 0 ¼ 7:4 ; 10 4 K. Using these results, we can compare the filters of the Shakura- Sunyaev disk model to a real filter. For example, the Sloan r 0 Size is everything : Investigation of quasar luminosity profiles on microlensing fluctuations Uniform disks, Gaussian disks, cones, Shakura-Sunyaev models: for circular disk models: Fig. 11. Dispersion (rms) of histograms from convolutions of both positive-parity (fluctuations ¼ ¼ 0:4; solid curves) are and relatively negative-parity insensitive ( ¼ ¼ 0:6; to all microlensing dashed curves) magnification maps with Gaussian disks (thin curves), uniform ð14þ properties disks (medium of the curves), models and cones (thick except curves). For the values half-light of r 1/2 greater than radius of the disk about 2r E, the six curves shown here are nearly indistinguishable. (Mortonson, Schechter & Wambsganss 2005) 29

30 Astrometric microlensing of quasars (Treyer & Wambsganss 2004) 30

31 Astrometric microlensing of quasars: (Treyer & Wambsganss 2004) 31

32 Quasar microlensing: The current achievements Quasar variability due to microlensing reveals: Effects of compact objects along the line of sight YES! Size of quasar PARTLY! Two-dimensional brightness profile of quasar NOT AT ALL! Mass (and mass function) of lensing objects SOME LIMITS! Detection of smoothly distributed (dark) matter STRONG HINTS! 32

33 Stellar Microlensing: Point lens and extended source 33

34 Near : Stellar Microlensing Paczynski (1986): MACHO, EROS, OGLE,... (from Sackett 1999) 34

35 Stellar microlensing: The current achievements Stellar variability due to microlensing reveals: Effects of Machos in Milky Way/galaxy halos Few (if any) dark compact objects in MW halo! Few (if any) dark compact objects in G0957 halo! Stars in the Milky Way disk/bulge/bar Plenty! and binaries! Mass measurement of lensing stars yes, very accurately! Surface brightness profile of distant stars yes! Cool dark matter 35

36 Stellar microlensing The current achievements A few highlights: results on Macho determination results on stellar mass measurements results on stellar surface structure results on planet searching 36

37 Stellar microlensing towards the LMC/SMC (illustration from MACHO team/website) 37

38 Stellar microlensing towards the LMC/SMC Dark Matter Detection? MACHO results (Alcock et al. 2001): events in 5.7 years consistent with 20% macho contribution to dark matter halo (still being debated what means: Sahu (2003), Belokurov & Evans (2005), Griest et al. (2005),...) EROS results (Milsztajn et al. 2000, Afonso et al. 2003): macho contribution 3% (95% confidence level), OGLE results (see also poster by Wyrzykowski): macho contribution is low, optical depth: (0.45±0.2) 10-7 Little (or no?) evidence for dark matter! 38

39 Stellar microlensing towards the Galactic Bulge: OGLE and MOA Microlensing events galore: more than 3000 events (> 600 this season by OGLE and MOA!): most single lens, many double lens/caustic crossing normal stars (binaries) acting as lenses! lots of interesting stellar/galactic astrophysics: masses, stellar surface structure, exo-planets 39

40 Stellar Microlensing: mass determination Jiang et al. (2004): OGLE-2003-BLG-238: Microlensing Mass Estimate of an Isolated Star microlensing is only known direct method to measure the masses of stars that lack visible companions required: measurement of both the angular Einstein radius θ E and the projected Einstein radius r E simultaneous measurement of these two parameters is extremely rare for OGLE-2003-BLG-238 (µ max = 170) with finite source effects: θ E = 650 µas, t E = 38 days constraints on microlens parallax: 4.4 < r E /AU < 18 I(OGLE) lens mass: 0.36 M < M < 1.48 M 14 estimate rather crude, however, demonstrates viability of technique 15! !.05 40

41 Stellar Microlensing: Studying Stellar Atmospheres Cassan et al. (2004): Probing the atmosphere of the bulge G5III star OGLE-2002-BLG-069 by analysis of microlensed Hα line A. Cassan, J.P. Beaulieu, S. Brillant et al.: Probing the atmosphere of a b Table 1. Model paramete with the SAAO 1.0m, U crolensing event OGLE tudes m (s) S and blend rat nary lens model to the co eters have been determin model with PHOENIX l around the caustic exit. Parameter V SAAO [I] ms 1 UTas [I] ms 1 ESO 2.2m [R] ms SAAO [I] g g UTas [I] 0 g ESO 2.2m [R] 0. Fig. 1. Equivalent-width variation of the Hα core (top panel) and ω as shown in Tab. is included in the list of 1999b), the best fit is41 ob

42 Stellar Microlensing: Studying Stellar Atmospheres Cassan et al. (2004): Probing the atmosphere of the bulge G5III star OGLE-2002-BUL-069 by analysis of microlensed Hα line 4 A. Cassan, J.P. Beaulieu, S. Brillant et al.: Probing the atmosphere of a bulge G5III star L4 A. Cassan et al.: Probing th Letter to the Editor Fig. 2. Upper panel: two UVES spectra (two lower curves) Fig. corresponding to 9 July, UT 22h59 (HJD = , at UT 00h04. July andat 10UT July, 00h04. UT 02h58. and 10 Notice July, the UTstrong 02h58. signature Noti 3. Same Fig. legend 3. Same as Fig. Legend 2 but as for Fig. the pair 2 but offor spectra the pair 9 Ju solid line) and 9 July at UT 00h04 (reference spectra, the HJD chromospheric signature Hαof emission. the chromospheric Hα emission = , dotted line), as well as two computed synthetic spectra at the same epochs (the two upper solid Joachim Wambsganss: Microlensing and synthetic Compact Objects in Galaxies and dotted curves). at: Applications Lower panel: of Gravitational fractional Lensing, difference KITP, δfsanta λ spectrum line) with at a radial each velocity epoch inof a consistent 7 kms 1, the way. sig = Barbara, amplified October at the 4, 2006 very end of caustic exit. 42 Fig. 2 we show the observed and synthetic spectra at tw

43 Stellar Microlensing: Studying Stellar Atmospheres Cassan et al. (2004): Probing the atmosphere of the bulge G5III star OGLE-2002-BLG-069 by analysis of microlensed Hα line High-resolution, time-resolved spectra of caustic exit of OGLE-2002-BLG-069 (UVES/VLT): A. Cassan, J.P. Beaulieu, S. Brillant et al.: source G5III giant in Galactic bulge strong differential magnification resolves stellar surface PHOENIX model lightcurve compared with photometric data and H α equivalent width agreement on gross features, discrepancies in details: excess amplified chromospheric emission after star s trailing limb outside caustic Letter to the Editor L4 A. Cassan et al.: Probing the atm Fig. 1. Equivalent-width variation of the Hα core (top panel) and wings (second panel from the top); the open circles in the plots of the equivalent-width variation correspond to our UVES data, while the adjoining solid lines represent the model predictions over the course of the caustic passage. The big dots correspond to the spectra of 10 July, UT 02H58. Third panel: model light curves and photometric data, where R-band data are plotted in red and I-band data in blue; model residuals from the chosen PHOENIX atmosphere (fourth panel) and from the linear limb-darkening law (bottom panel), with the same color convention. The model parameters can be found in Tab. 1. The majority of model residuals are below the 2 % level. The post caustic observations have been plotted at , but have Fig. 3. Same legend as Fig. 2 but for the pair of spectra 9 July been taken on 16 August. at UT 00h04. and 10 July, UT 02h58. Notice the strong signature of 43

44 Stellar Microlensing: Searching for extrasolar planets simulation by Scott Gaudi: star-plus-planet lens 44

45 Stellar Microlensing: Searching for extrasolar planets The 24 hour night shift: PLANET telescope sites PLANET - Probing Lens Anomaly NETwork 45

46 Stellar Microlensing: Finding extrasolar planets Vol January 2006 doi: /nature04441 LETTERS Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing J.-P. Beaulieu 1,4, D. P. Bennett 1,3,5, P. Fouqué 1,6, A. Williams 1,7, M. Dominik 1,8, U. G. Jørgensen 1,9, D. Kubas 1,10, A. Cassan 1,4, C. Coutures 1,11, J. Greenhill 1,12, K. Hill 1,12, J. Menzies 1,13, P. D. Sackett 1,14, M. Albrow 1,15, S. Brillant 1,10, J. A. R. Caldwell 1,16, J. J. Calitz 1,17, K. H. Cook 1,18, E. Corrales 1,4, M. Desort 1,4, S. Dieters 1,12, D. Dominis 1,19, J. Donatowicz 1,20, M. Hoffman 1,19, S. Kane 1,21, J.-B. Marquette 1,4, R. Martin 1,7, P. Meintjes 1,17, K. Pollard 1,15, K. Sahu 1,22, C. Vinter 1,9, J. Wambsganss 1,23, K. Woller 1,9, K. Horne 1,8, I. Steele 1,24, D. M. Bramich 1,8,24, M. Burgdorf 1,24, C. Snodgrass 1,25, M. Bode 1,24, A. Udalski 2,26, M. K. Szymański 2,26, M. Kubiak 2,26, T. Więckowski 2,26, G. Pietrzyński 2,26,27, I. Soszyński 2,26,27, O. Szewczyk 2,26, Ł. Wyrzykowski 2,26,28, B. Paczyński 2,29, F. Abe 3,30, I. A. Bond 3,31, T. R. Britton 3,15,32, A. C. Gilmore 3,15, J. B. Hearnshaw 3,15, Y. Itow 3,30, K. Kamiya 3,30, P. M. Kilmartin 3,15, A. V. Korpela 3,33, K. Masuda 3,30, Y. Matsubara 3,30, M. Motomura 3,30, Y. Muraki 3,30, S. Nakamura 3,30, C. Okada 3,30, K. Ohnishi 3,34, N. J. Rattenbury 3,28, T. Sako 3,30, S. Sato 3,35, M. Sasaki 3,30, T. Sekiguchi 3,30, D. J. Sullivan 3,33, P. J. Tristram 3,32, P. C. M. Yock 3,32 & T. Yoshioka 3,30 46

47 Stellar Microlensing: Finding extrasolar planets Time in days

48 Stellar Microlensing: Finding extrasolar planets Microlensing event OGLE-2005-BLG-390: produced by star-plus-planet system with mass ratio most likely (with model of Milky Way): star of 0.2 solar masses planet of 5.5 Earth masses (instantanous) separation 2.6 AU orbital period 10 years 48

49 Stellar microlensing: The current achievements Stellar variability due to microlensing reveals: Effects of Machos in Milky Way/galaxy halos Few (if any) dark compact objects in MW halo! [Few (if any) dark compact objects in G0957 halo!] Stars in the Milky Way disk/bulge/bar Plenty! and binaries! Mass measurement of lensing stars yes, very accurately! Surface brightness profile of distant stars yes! Cool dark matter yes, 4 planets so far (cool!) 49

50 Summary The future of gravitational microlensing for measuring the surface brightness profiles of quasars as a function of wavelength for determining the mass scale, mass function, dark matter content of lensing objects in the galaxies for detecting compact objects in the Milky Way, in particular extrasolar planets from a curiosity into a tool... (Kochanek et al., September 2006)... is bright! 50