Strong Gravitational-Lensing by Galaxies: 30 years later...

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1 Strong Gravitational-Lensing by Galaxies: 30 years later... Léon Koopmans ( Institute (Kapteyn Astronomical Stellar Dynamics Gravitational lensing JENAM - April 22, 2009

2 Some Applications of Galaxy Lensing Galaxy Structure, Formation & Evolution DM & Baryonic Density Profiles Scaling relations: e.g. FP (CDM) Mass-substructure ISM Cosmological Parameters Individual Galaxies: Hubble Constant Lensing Statistics: Cosmography Natural Telescope Quasar Microlensing Delensing of source Too much to cover in 30 min; I will show some recent examples

3 State of the Art Lens Surveys Strong-lenses are rare occurences: optical depth is 10-3, hence large surveys to find lens-candidates are required Radio: source selection/few biases MG/PMN/PANELS surveys: around 5-10 galaxy-scale lenses JVAS/CLASS: 22 galaxy-scale lenses Optical Imaging: source/lens selection HE/HQS & SDSS quasars: 1-2 dozen lenses HST MDS/Optical HST Snapshot survey: 5-10 each CFHT LS: around 100 galaxy/group lens candidates Spectroscopic: Lens selection SLACS: around 100 confirmed lenses OLS: 5-10 confirmed lenses

4 Galaxy-scale Strong Lens Surveys CLASS: Radio-selected - Source selected - Few biases based on lens galaxy - Small image separations - No dust extinction (but scattering?) - State of the art: >10 4 targets - Lensing rate: 1/700 - Results: 22 confirmed lenses

5 Galaxy-scale Strong Lens Surveys SLACS: Spectroscopy-selected - Lens selected - Uniform lens-galaxy criteria: E/S0 - Emission-line selection - Blue starforming source provides good lens/source contrast - State of the art: few x 10 5 targets - Lensing rate: ~1/ Results: ~100 confirmed lenses

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7 SWELLS: Not only early-type galaxies, also spirals Image Residuals Image Residuals Credit: Matt Auger Ongoing HST/WFPC2 programme

8 Modern Integrated Approach Combining Strong Lensing with other tools...

9 Modern Integrated Approach Baryonic + Dark Matter around the Einstein Radius CDM Substructure Grid-based methods Strong Lensing Transition regions between stellar and DM components. Hydrostatic eqns. X-ray Observ. Breaking Degeneracies (mass-anisotropy, ( inclination mass-sheet, Stellar Dynamics Baryonic + Dark Matter around the effective radius Phase-space density Grid-based methods Weak Lensing Environment & Outer DM halo Grid-based methods

10 Strong Lensing Geometry S θ L β O Lens equation: β = θ α ( θ) Non-linear -> Multiple solutions

11 Defection Angle and Density profiles Pointmass SIS Moore Kochanek, Schneider & Wambsganss 2004

12 Example: B Radio jet lensed by spiral galaxy at z=0.9 Note the very similar radial stretching of the lensed images compared to the source γ r 1.96±0.02 Wucknitz et al 2002

13 Lensing & Dynamics Increasing the diagnostic power of lensing

14 Scale-free toy model Let us assume that the density and luminosity densities are scale-free power-law distributions And that the (an)isotropy is constant as function of radius to first approximation

15 Scale-free toy model The spherical Jeans equation can analytically be solved: Or averaged inside an aperture: Koopmans 2004

16 Combining with Stellar Dynamics Constant M/L model versus SIS R 1/4 constant M/L density profile Lensing mass is the same SIS density profile with stellar M/L=0

17 The structure of E/S0 galaxies ( systems Analysis of full HST-ACS sample (58 Isothermal Density Profiles It is not well understood why baryonic & DM add to a combined 1/r 2 density profile, despite different physics and starting conditions. Or is this an efect of modified gravity? ( prep Koopmans et al (in

18 The structure of E/S0 galaxies No correlations with anything whatsoever? Analysis of the SLACS-ACS sample with good lensing & kinematic data shows no dependence of the slope on (i) galaxy properties, (ii) redshift or (iii) environment ( prep Koopmans et al (in

19 Lensing & Dynamics: Density Slope at z=0.5 (Warren et al. 1996) Koopmans & Treu 2003

20 Lensing & Dynamics: Anisotropy 5.75 hrs integration with Keck/ESI; velocity dispersion profile to ~5 % DM density slope Stellar mass fraction Koopmans & Treu 2003

21 Lensing & Dynamics: Separating Stellar and Dark Matter LSD Survey Two component mass models: >> Isotropic models (R i ="): 44 <! DM > = (68% CL) >> Anisotropic models (R i =R eff ): <! DM > < 0.6 (68% CL) Treu & Koopmans 2004

22 Self-consistent lensing & Stellar Dynamics Going beyond spherical Jeans modelling

23 A SELF-CONSISTENT METHOD FOR LENSING AND DYNAMICS ANALYSIS Barnabè & Koopmans 2007 Axisymmetric density distribution: ρ(r,z) Gravitational potential: Φ(R,z,η k ) linear optimization LENSED IMAGE REC. linear optimization DYNAMICAL MODEL Maximize the Bayesian evidence allows model comparison automatically embodies Occam s razor (MacKay 1992) when converges non-linear optimization vary η k Best values for the non-linear parameters η k source reconstruction & DF reconstruction

24 Monte Carlo 2-Integral f(e,l z ) Schwarzschild method DF Σ v σ Barnabè & Koopmans 2007 TIC 2 TIC 1 TIC = total

25 Dynamical Model = DF reconstruction DF Σ < v z' > < v 2 z' > residuals reconstructed mock

26 This method is being applied to VLT VIMOS data from an ESO Large Programme & Keck Data See talk by Oliver Czoske for results...

27 Weak Lensing of Strong Lenses Going beyond the baryons...

28 Weak Lensing of Strong Lenses 22 lenses (z~ ) with velocity dispersion ~ km/s F814W/ACS images (1 orbit) with FOV 200''x200'' Large surface density of sources I AB < 26.2 n bg ~80 arcmin -2. Gavazzi et al. 2008

29 Weak Lensing of Strong Lenses 2D mass mapping => ellipticity of haloes? Gavazzi et al. 2008

30 Weak Lensing of Strong Lenses Shear measure over kpc DeVauc+NFW Fit+concentration index from numerical sims: M * /L V = 4.4 ± 0.5 M sun /L sun M vir /L V = 350 ± 150 M sun /L sun 27±4% DM inside a sphere of 1 effective radius Gavazzi et al. 2008

31 Early-type Galaxy Scaling Relations A (More) Fundamental Plane?

32 The Fundamental Plane Massive elliptical occupy a Fundamental Plane in the space of effective radius, effective surface brightness and central velocity dispersion (e.g. Dressler et al. 1987; Djorgovski & Davis 1987) Also SLACS E/S0's occupy the same FP as their parent population from the LRG and MAIN SDSS samples.

33 A More Fundamental Plane? On the other hand, the virial theorem tells us: Why do the slopes differ from the FP? (M/L) varies with galaxy mass, i.e velocity dispersion, or structural non-homology?

34 A More Fundamental Plane? Idea: Replace surface brightness by surface density

35 Scaling Relations: The Fundamental Plane reference lines Lens and dynamical masses ( σ 2 R eff ) scale linearly Masses do NOT scale linearly with V luminosity

36 The structure of E/S0 galaxies ( constant Dark matter inside one effective radius (stellar M/L ~ Sauron: Stellar M/L (Cappellari et al 2006) ( prep Koopmans et al (in DM mass fraction increases dramatically from <L* to >L* ( km/s (up to 50% for σ~350 (if the IMF does not change strongly with galaxy mass)

37 (CDM) Mass Substructure More than meets the eye!

38 Grid-based Lensing Simulated Massive Galaxy Observed Massive Galaxy Smooth Dark Matter Stars Clumpy Dark Matter Modeling must be more sophisticated than simply parameterized!

39 Why can we detect mass substructure? d β d θ = ( ) 1 κ γ1 γ 2 γ 2 1 κ + γ 1 Note that near critical curves, the determinant of the inverse magnification matrix go to zero. We can use this matrix (assume κ=γ) and add a perturbation δ β = ( ) ɛ δκ δγ1 δγ 2 δγ 2 1 δκ + δγ 1 δ θ We note that near the critical curves, a small perturbation can cause large tangential changes in the images.

40 Lensing near critical curves is sensitive to CDM substructure Text Xu et al.2009 Mathematical relations between image fluxes (fold/cusp relations break down due to perturbations -> indication of substructure

41 Lensing near critical curves is sensitive to CDM substructure? The level of substructure affects by how much the cusp/fold relations are broken and can thus be used to measure the CDM substructure mass fraction Bradac et al. 2004

42 Lensing near critical curves is sensitive to CDM substructure? Dalal & Kochanek (2002) set limits on f CDM based a half a dozen radio lenses with anomalous cusp/fold relations However: (1) The mass fraction seems too high (2) There are clear problems with some systems, indicating some systematic effects (scattering, microlensing, etc). The jury is still out on this!

43 A Differential-Lens Equation To solve for (i) the source brightness distribution and (ii) the potential, using S x ( x) =S y ( y, ψ( x)) Conservation of source surface brightness with y = x ψ( x) The usual lens equation Koopmans (2009), in prep.

44 Linearized Differential Equation Linear Expansion in algebraic form this reads: (Koopmans et al 2005; Suyu et al. 2006/8; Vegetti & Koopmans 2008) This linear algebraic equation can be solved using a Bayesian penalty function for the residuals and standard Cholesky/gradient methods This is what we have used so far with great success

45 CDM Substructure & Strong Lensing No Substructure Dark substructure mass = 10 9 solar mass Best smooth model Best non-smooth model Vegetti & Koopmans, 2009

46 Detecting CDM Substructure M sub = 0 M sub = 10 7 M M sub = 10 9 M Vegetti & Koopmans 2009 Region affected by substructure θ µ θ ER

47 Detecting CDM Substructure 14 lens models: 1 smooth Power-Law: 12 PL + NFW: 4 positions x 3 masses 1 PL + 2 NFW Extended source with Gaussian surface brightness profile SLACS J M NFW = 10 7, 10 8, 10 9 M Vegetti & Koopmans 2009

48 Detecting CDM Substructure All substructures on the ring with mass different significance levels: M sub 10 7 M are detected at log(e) = 17.1 log(e) = All substructures outside/inside the ring with mass detected M sub 10 9 M log(e) = ; are Systems with two substructures and external shear can be reconstructed at the noise level log(e) = Vegetti & Koopmans 2009

49 Double Einstein Ring SDDS J : Simulations dn/dm m α α = 2.0 f(3re) = 1.0% Vegetti et al., in prep

50 Double Einstein Ring SDDS J : Simulations Bayesian adaptive grid-based reconstruction can even recover perturbations more complex than a single substructure Vegetti & Koopmans 2009; Vegetti et al. 2009, in prep.

51 Next Steps - The Future for Strong Galaxy-Galaxy Lensing VLT X-shooter: UV-IR Spectroscopy of massive lenses to assess their ( Koopmans true stellar M/L to z=1 (22hrs GTO time; PI. ELT, OPTIMOS (ESO Phase-A study since Sept. 2008): Spatially-resolved kinematics and stellar population of E/S0 galaxies at z 1 (co-i). SKA, LOFAR, e-merlin, EVLA, LSST, Pan-STARRS, follow-up w/jdem, JWST, ALMA etc.: Large all-sky surveys to discover 1000s of new lenses ( 2009 al. (e.g. Koopmans, Jackson & Browne 2004; Koopmans et al. 2009; Marshall et Other ongoing surveys e.g.: COSMOS (Faure et al. 2008), CFHT (Cabanac et al. 2007),,(. al GOODS (Moustakas et al. 2006), HAGLeS (Marshall et SLQS (Gavazzi et al.), etc...

52 General Conclusions (Strong) Gravitational Lensing provides a unique tool to measure stellar & DM density profile in the region of galaxies, where DM-Baryon interactions are important. Strong lensing (by galaxies) can detect and quantify (CDM) mass substructure in the range of solar mass and up. Lensing provide a unique probe in to the study of DM and possibly alternative (metric) gravity theories. (see e.g. white papers on astro-ph by Koopmans et al, Marshall et al. and Moustakas et al. 2009)