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Weak Lensing at the LBT and DES – some initial results

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  1. Weak Lensing at the LBT and DES – some initial results M.S.S. Gill, in collaboration with J. Young, K.Honscheid, D.Weinberg, C.Kochanek, P.Martini, E.Rozo of the OSU CCAPP, and with members of the DES WL Subgroup Tues Feb 17, 2009 – Los Alamos Nat’l Lab, T2 Division

  2. Outline • Introduction and Motivations • Weak Lensing (WL) pipelines description • Simulation tests • Cluster Observations • Abell 611 systematic tests and results • Future projections

  3. DM (Dark Matter) in many spheres Galaxy Dynamics Particle Theory Colliders Cosmological Component

  4. How is WL Useful as a Cosmological Probe of DM? • Better systematics than other probes • Gravitational only, no baryonic physics needed • Issue: Must deal with PSF (Point Spread Function) • Two domains: cluster and cosmological shear

  5. z = 7 dark matter z = 5 z = 3 time z = 0.5 z = 0 z = 1 Cluster Weak Lensing • We can determine some of the cosmological parameters from cluster WL, using: • 1. Total mass of cluster at a given z • 2. Concentration of radial mass profiles 5 Mpc Kravtsov

  6. Ohio State Weak Lensing Survey (OWLS) Project Goals • Three-band (ugr) picture of Abell 611 from the LBT: • Constraining cosmological parameters with • cluster weak (and potentially strong) lensing

  7. LBT OWLS Projections • Current best constraints (WMAP+SDSS+SNIa): • s8= 0.77 +/- 0.05, w = -0.93 +/- 0.08 • Wm = 0.27 +/- 0.04, WL = 0.73 +/- 0.04 • Projections for LBT with several clusters: Assumes lensing using 50 richest clusters in observed 250 degree squared field with all background (lensed) galaxies at z=0.6 Colors are 1,2,3 s contours Here: s8 vs. Wm s8 Wm (Plot: J. Yoo)

  8. Other Parameters from OWLS Here: w vs. s8 and w vs. Wm s8 Wm (Plot: J. Yoo)

  9. Fundamentals of WL

  10. Lensing Effect on Background Galaxies Foreground Cluster Background Source shape Note: the effect has been greatly exaggerated here (Orig Figure: S.Dodelson)

  11. Basic Weak Lensing Geometry Mass Profile of Lens Deflection Angle: (Narayan+Bartelmann, 1997)

  12. Simple Picture of How Galaxy Shapes are Distorted by WL Light rays bent less than middle of disk, this part of image looks closer to cluster center Middle of disk Light rays bent more than middle of disk, this part of image looks farther from cluster center Tracing light rays, shape transforms to an ellipsoidal form

  13. SIS (Singular Isothermal Sphere) Shear Profile

  14. Observer Lensing mass Source Analogy to Probing the Insides of a Hadron • Translate to mass profile – can analogize to extracting form factor (~wavefunction) of a hadron) Contains Mass Profile Information

  15. To do the WL: Parallel Pipelines • We run two codes in parallel, shapelets and imcat • Shapelets: based on decomposing galaxy shapes into orthonormal 2D basis functions (IDL-implemented) • Imcat: measures shapes via weighted quadrupole moments (C and PERL-based) • We remove the PSF in both and then give the fit shear profiles in the end

  16. Shapelets (polar form) Objects decomposed into a set of orthogonal basis functions with explicit rotational symmetry (Hermite-Laguerre polynomials) Idea: -- Decompose foreground stars to characterize PSF -- Decompose all candidate background galaxies to extract shape information Massey et al. (2007)

  17. Example Decomposition Decomposition of stars and galaxies into shapelets coefficients reduces removal of PSF anisotropies into a linear algebra problem Massey & Refregier (2005)

  18. Screen clipping taken: 2/11/2009, 8:17 PM Imcat Formalism Outline (1) First remove the anisotropic part of the PSF (epsilon = ellipticity, cor = corrected, obs = observed, Psm= matrix of PSF anisotropy, p = stellar polarization)

  19. Screen clipping taken: 2/11/2009, 8:17 PM Imcat Formalism Outline (2) Then remove the isotropic part of the PSF (epsilon = ellipticity,, Psh= matrix of PSF isotropic smearing)

  20. Tests on simulations • STEP2 constant shear and constant PSF simulations • SimpleSim Artificial Cluster test – constant PSF • DES Cluster Simulation – varying PSF

  21. Does ellipticity go to zero on half the stars after deconvolution from the other half? (STEP2) Originally from sextractor: Mean e1 ~ .06, Mean e2 ~ -.005 Lower order has mean e1,2 closer to zero, and smaller dispersion

  22. STEP2 Shapelets Results – ADE Avg Average of PSF’s A,D,E – compared with STEP2 groups Squares = rotation-matched Triangles = original only Red square = our result

  23. Artifical Simple Simulated Cluster Test Given 2 fields: galaxies and stars, with same applied PSF 250 objects in ‘galaxy’ field All at same bkgd z of 1 Constant direction PSF Represented by ‘stars’ – Originally circular objects

  24. More realistic: the Dark Energy Survey (DES) Probe the nature of dark energy with • Supernovae • Baryon oscillations • Clusters of galaxies • Weak gravitational lensing

  25. DES Projection for Sky Coverage Blanco 4-m Optical Telescope at CTIO: 5000 sq. deg. Dark Energy Survey (Fig: J.Frieman)

  26. Screen clipping taken: 2/17/2009, 7:26 AM DES Projections Again, current best cosmological parameters: • s8= 0.77 +/- 0.05, w = -0.93 +/- 0.08 • Wm= 0.27 +/- 0.04 , WL = 0.73 +/- 0.04 And projections from DES: WL

  27. DES Cluster Simulation • All 62 chips are done (H. Lin and N. Kouropatkin) • Stepped up in increasing complexity: • Start with just background galaxies • Add in shear • Add in noise • Add in psf • Add in stars • Add in cluster and foreground galaxies

  28. Mag vs. FWHM plot

  29. Full Field Simulation Model psf From stars (Imcat)

  30. Screen clipping taken: 2/17/2009, 2:43 AM SIS Fits to the DES simulation Shear vs. radial distance from center in pixels After PSF correction, shear matches truth within error Sextractorellip = pink solid Truth = red solid Shear = dashed

  31. A611 and other Cluster Data

  32. The Large Binocular Telescope • At 10.7k feet in Eastern AZ • Two 8.4m mirrors, full collecting area = single mirror of 11.8 m

  33. Observations : Better than 0.8” Seeing Statistics • Science Definition Time -- 2007 • Two clusters (Abell 611 and MS1358) observed • Spring/Summer 2008 • Four clusters (Abell 1835, MAX3, MAX5, MAX8) were observed

  34. 2008 Observations: in g- and i- bands MAX3 Abell 1835 MAX5 g i

  35. 2007: Images of A611 r-band g-band u-band Used IRAF and SCAMP/SWARP to reduce the raw images (astrometry matched to SDSS star catalogs)

  36. Star / Galaxy Separation Better to use flux_radius vs. fwhm for defining star column • Mag vs. Flux_radius Mag vs. FWHM Much clearer star column demarcation.

  37. A611 – PSF Structure Each chip treated separately, Model of the PSF interpolated from the stellar ellipticities; notice continuity of PSF across the chip boundaries. (This is in fact 4 overlayed ps files). (A611 g-band file)

  38. PSF checks – ellipticity of stars after PSF removal for A611 Order 2 PSF Order 0 PSF Order 3 PSF Orig Ellip Post PSF Sub. Ellip

  39. Behavior of ellipticity as a function of order in a stars on stars test (A611) Originally from sextractor: Mean e1 ~ .0009, Mean e2 ~ 0.0036, sigma(e1) = 0.044, sigma(e2) = 0.043 for about 190 stars. Order 3 onwards has stable small dispersion in e1,2

  40. Shapelets, Stars on Stars Original: Shapelet Model: After PSF deconvolution-- Note near delta function for stellar flux

  41. Correlation Tests: Random Stars

  42. Correlation of Stars in A611 Before and after psf correction: more correlated before, and falls with distance , less afterwards, increases to the random value with distance.

  43. Foreground vs. Background Galaxy Rejection (1) G-R vs. U-G, CFHT (D1 sample) (red = zp > 0.3, green = zp <0.3)

  44. Foreground vs. Background Galaxy Rejection (2) G-R vs. U-G, CFHT (D1 sample) Showing the effect of color cuts in isolating Bkgd sample (Red = zp > 0.3, Green = zp < 0.3 )

  45. CFHT cuts: zp distributions after color cuts (D1 field) Black = all Blue = color-selected foreground Orange = color-selected bkgd

  46. Test: Eprofiles around points far from nominal cluster center (A611) Profiles around center and 8 surrounding points Around center and average of 8 surrounding points

  47. A611 Profiles: Compare whole field vs. separate chips processing Shear vs. radial distance from center in pixels Not so much dif. at least in the E-mode profiles Number of objects here: Whole field: 8185 Sep chips: 8227

  48. Bootstrap tests: Galaxies varying E and B mode profiles for 100 galaxy variations for A611 (pick 9964 galaxies from the set of 9964 100 times, and make profiles) E profile B profile

  49. Bootstrap tests: PSF varying E and B mode profiles for 100 psf variations for A611 (pick 499 star from the set of 499 100 times, construct psf, make profiles) E profile B profile

  50. Bootstrap tests: both varying, E profile E and B mode profiles for 100 galaxy AND PSF variations for A611 (pick randomly from 9964 galaxies and 499 stars 100 times, and make profiles) E profile B profile