D. Smith

University of Michigan, Ann Arbor, MI, United States

Are you D. Smith?

Claim your profile

Publications (4)4.97 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We measure seeing-corrected ellipticities for 2 × 106 galaxies with magnitude R ≤ 23 in 12 widely separated fields totaling 75 deg2 of sky. At angular scales 30', ellipticity correlations are detected at high significance and exhibit nearly the pure "E mode" behavior expected of weak gravitational lensing. Even when smoothed to the full field size of 25, which is ≈25 h-1 Mpc at the lens distances, an rms shear variance of γ21/2 = 0.0012 ± 0.0003 is detected. At smaller angular scales, there is significant "B-mode" power, an indication of residual uncorrected point-spread function distortions. The data at scales above 30' constrain the power spectrum of matter fluctuations on comoving scales of ≈10 h-1 Mpc to have σ8(Ωm/0.3)0.57 = 0.71 (95% confidence level, ΛCDM, Γ = 0.21), where the systematic error includes statistical and calibration uncertainties, cosmic variance, and a conservative estimate of systematic contamination based upon the detected B-mode signal. This normalization of the power spectrum is lower than, but generally consistent with, previous weak-lensing results, is at the lower end of the σ8 range from various analyses of galaxy cluster abundances, and agrees with recent determinations from cosmic microwave background and galaxy clustering. The large and dispersed sky coverage of our survey reduces random errors and cosmic variance, while the relatively shallow depth allows us to use existing redshift survey data to reduce systematic uncertainties in the N(z) distribution to insignificance. Reanalysis of the data with more sophisticated algorithms will hopefully reduce the systematic (B mode) contamination and allow more precise, multidimensional constraint of cosmological parameters.
    The Astronomical Journal 12/2007; 125(3):1014. · 4.97 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We measure seeing-corrected ellipticities for 2 x 10^6 galaxies with magnitude R<23 in 12 widely separated fields totalling 75 deg^2 of sky. At angular scales >30\arcmin, ellipticity correlations are detected at high significance and exhibit nearly the pure "E-mode" behavior expected of weak gravitational lensing. Even when smoothed to the full field size of 2.5 degrees, which is ~25h^-1 Mpc at the lens distances, an rms shear variance of <\gamma^2>^1/2 = 0.0012 +- 0.0003 is detected. At smaller angular scales there is significant "B-mode" power, an indication of residual uncorrected PSF distortions. The >30\arcmin data constrain the power spectrum of matter fluctuations on comoving scales of ~10h^-1 Mpc to have \sigma_8 (\Omega_m/0.3)^{0.57} = 0.71^{+0.12}_{-0.16} (95% CL, \LambdaCDM, \Gamma=0.21), where the systematic error includes statistical and calibration uncertainties, cosmic variance, and a conservative estimate of systematic contamination based upon the detected B-mode signal. This normalization of the power spectrum is lower than previous weak-lensing results but generally consistent them, is at the lower end of the \sigma_8 range from various analyses of galaxy cluster abundances, and agrees with recent determinations from CMB and galaxy clustering. The large and dispersed sky coverage of our survey reduces random errors and cosmic variance, while the relatively shallow depth allows us to use existing redshift-survey data to reduce systematic uncertainties in the N(z) distribution to insignificance. Reanalysis of the data with more sophisticated algorithms will hopefully reduce the systematic (B-mode) contamination, and allow more precise, multidimensional constraint of cosmological parameters.
    11/2002;
  • Source
    12/2000; 237:299.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Until now, direct studies of the mass distribution in clusters of galaxies via weak gravitational lensing have focused on rare optically rich or X-ray luminous clusters. We present results from a weak lensing survey of eight X-ray selected ``normal" clusters at z ~ 0.2. The clusters were chosen to have L_X &lsim; L_{star ,X}, to match typical clusters in the nearby universe. For each cluster, we have obtained deep Bj, R and I images over a 50' square field using the Big Throughput Camera (BTC) CCD mosaic (Tyson, Bernstein, Blouke, & Lee 1992, SPIE 1656, 400; Wittman, etal. 1998, SPIE 3355, 626) at the Blanco 4-meter on Cerro Tololo. The multicolor photometry allows separation of foreground cluster and background galaxies. We have analyzed the statistical distortion (shear) of the faint blue background galaxy shapes in these fields and derived mass maps and radial mass profiles for each cluster. We present the first results from the survey, including the mean radial profile out to R > 3h(-1) Mpc, substructure statistics, mass-to-light ratio, and statistics on the presence of other mass concentrations within our survey fields. Calibration and simulation data are also presented.
    12/1998;