397 research outputs found

    Gravity and Non-gravity Modes in the VIRMOS-DESCART Weak Lensing Survey

    Get PDF
    We analyze the weak lensing data of the VIRMOS imaging survey using projections (called E and B-modes) of the two independents observed correlation functions. The E-mode contains all the lensing signal, while noise and systematics contribute equally to the E and B modes provided that intrinsic alignment is negligible. The mode separation allows a measurement of the signal with a \sqrt{2} smaller error bars, and a separate channel to test for systematic errors. We apply various transformations, including a spherical harmonic space power spectrum C^E_l and C^B_l, which provides a direct measurement of the projected dark matter distribution for 500<l<10^4.Comment: accepted version, minor changes, 18 pages including 6 figure

    Cross-Correlating Probes of Primordial Gravitational Waves

    Full text link
    One of the most promising ways of detecting primordial gravitational waves generated during inflation is to observe B-modes of polarization, generated by Thomson scattering after reionization, in the cosmic microwave background (CMB). Large scale foregrounds though are expected to be a major systematic issue, so -- in the event of a tentative detection -- an independent confirmation of large scale gravitational waves would be most welcome. Previous authors have suggested searching for the analogous mode of cosmic shear in weak lensing surveys but have shown that the signal to noise of this mode is marginal at best. This argument is reconsidered here, accounting for the cross-correlations of the polarization and lensing B-modes. A lensing survey can potentially strengthen the argument for a detection of primordial gravitational waves, although it is unlikely to help constrain the amplitude of the signal.Comment: 13 pages, 8 figure

    Measuring the Deviation from the Linear and Deterministic Bias through Cosmic Gravitational Lensing Effects

    Full text link
    Since gravitational lensing effects directly probe inhomogeneities of dark matter, lensing-galaxy cross-correlations can provide us important information on the relation between dark matter and galaxy distributions, i.e., the bias. In this paper, we propose a method to measure the stochasticity/nonlinearity of the galaxy bias through correlation studies of the cosmic shear and galaxy number fluctuations. Specifically, we employ the aperture mass statistics MapM_{ap} to describe the cosmic shear. We divide the foreground galaxy redshift zf<zsz_f<z_s into several bins, where zsz_s is the redshift of the source galaxies, and calculate the quantity 2/^2/ for each redshift bin. Then the ratio of the summation of 2/<Ng2(zf)>^2/< N_g^2(z_f)> over the bins to gives a measure of the nonlinear/stochastic bias. Here Ng(zf)N_g(z_f) is the projected surface number density fluctuation of foreground galaxies at redshift zfz_f, and MapM_{ap} is the aperture mass from the cosmic-shear analysis. We estimate that for a moderately deep weak-lensing survey with zs=1z_s=1, source galaxy surface number density nb=30gal/arcmin2n_b=30 \hbox {gal}/\hbox {arcmin}^2 and a survey area of 25deg225 \hbox {deg}^2, the effective rr-parameter that represents the deviation from the linear and deterministic bias is detectable in the angular range of 1'-10' if |r-1|\gsim 10%. For shallow, wide surveys such as the Sloan Digital Sky Survey with zs=0.5z_s=0.5, nb=5gal/arcmin2n_b=5 \hbox {gal}/\hbox {arcmin}^2, and a survey area of 104deg210^4 \hbox {deg}^2, a 10% detection of rr is possible over the angular range 11001'-100'.Comment: ApJ in pres

    Cross-correlating CMB polarization with local large scale structures

    Get PDF
    We study heterogeneous quantities that efficiently cross-correlate the lensing information encoded in CMB polarization and large-scale structures recovered from weak lensing galaxy surveys. These quantities allow us to take advantage of the special features of weak lensing effect on CMB B-polarization and of the high (40%) cross-correlation between the two data sets. We show that these objects are robust to filtering effects, have a low intrinsic cosmic variance (around 8% for small 100 square degrees surveys) and can be used as an original constraint on the vacuum energy density.Comment: 4 pages, use moriond.sty, to appear in the proceedings of the XXXVth Rencontres de Moriond "Energy densities in the Universe