1,548 research outputs found

    Lensing Sunyaev-Zel'dovich Clusters

    Get PDF
    Full-sky microwave surveys like the upcoming Planck satellite mission will detect of order 10^4 galaxy clusters through their thermal Sunyaev-Zel'dovich effect. I investigate the properties of the gravitationally lensing subsample of these clusters. The main results are: (1) The combined sample comprises >~70% of the complete sample. (2) It is confined to redshifts 0.2+-0.1, and to masses (5+-3) x 10^14 solar masses. (3) Using a particular measure for the weak lensing effect, viz. the aperture mass, cluster masses can be determined with a relative accuracy of ~20% if their density profile is known. Consequently, the mass function of the combined sample can accurately be measured. (4) For low-density universes, I predict a sharp peak in the measured (aperture) mass function near 5 x 10^14 solar masses and explain its origin, showing that the peak will be absent in high-density universes. (5) The location of the peak and the exponential decrease of the mass function on its high-mass side will allow the determination of the amplitude of the dark-matter power spectrum on the cluster scale and the baryon fraction in clusters, and constrain the thermal history of the intracluster gas.Comment: submitted to Astronomy & Astrophysic

    Cosmological Information from Quasar-Galaxy Correlations induced by Weak Lensing

    Get PDF
    The magnification bias of large-scale structures, combined with galaxy biasing, leads to a cross-correlation of distant quasars with foreground galaxies on angular scales of the order of arc minutes and larger. The amplitude and angular shape of the cross-correlation function w_QG contain information on cosmological parameters and the galaxy bias factor. While the existence of this cross-correlation has firmly been established, existing data did not allow an accurate measurement of w_QG yet, but wide area surveys like the Sloan Digital Sky Survey now provide an ideal database for measuring it. However, w_QG depends on several cosmological parameters and the galaxy bias factor. We study in detail the sensitivity of w_QG to these parameters and develop a strategy for using the data. We show that the parameter space can be reduced to the bias factor b, Omega_0 and sigma_8, and compute the accuracy with which these parameters can be deduced from SDSS data. Under reasonable assumptions, it should be possible to reach relative accuracies of the order of 5%-15% for b, Omega_0, and sigma_8. This method is complementary to other weak-lensing analyses based on cosmic shear.Comment: 11 pages, 7 figures, accepted for publication in Astronomy and Astrophysic

    Triaxial collapse and virialisation of dark-matter haloes

    Full text link
    We reconsider the ellipsoidal-collapse model and extend it in two ways: We modify the treatment of the external gravitational shear field, introducing a hybrid model in between linear and non-linear evolution, and we introduce a virialisation criterion derived from the tensor virial theorem to replace the ad-hoc criterion employed so far. We compute the collapse parameters delta_c and Delta_v and find that they increase with ellipticity e and decrease with prolaticity p. We marginalise them over the appropriate distribution of e and p and show the marginalised results as functions of halo mass and virialisation redshift. While the hybrid model for the external shear gives results very similar to those obtained from the non-linear model, ellipsoidal collapse changes the collapse parameters typically by (20...50)%, in a way increasing with decreasing halo mass and decreasing virialisation redshift. We qualitatively confirm the dependence on mass and virialisation redshift of a fitting formula for delta_c, but find noticeable quantitative differences in particular at low mass and high redshift. The derived mass function is in good agreement with mass functions recently proposed in the literature.Comment: 9 pages, 9 figures, published in Astronomy and Astrophysics; slight modifications to match the published versio

    QSO-galaxy correlations due to weak lensing in arbitrary Friedmann-Lemaitre cosmologies

    Get PDF
    We calculate the angular cross-correlation function between background QSOs and foreground galaxies induced by the weak lensing effect of large-scale structures. Results are given for arbitrary Friedmann-Lemaitre cosmologies. The non-linear growth of density perturbations is included. Compared to the linear growth, the non-linear growth increases the correlation amplitude by about an order of magnitude in an Einstein-de Sitter universe, and by even more for lower Omega_0. The dependence of the correlation amplitude on the cosmological parameters strongly depends on the normalization of the power spectrum. The QSO-galaxy cross-correlation function is most sensitive to density structures on scales in the range (1-10) Mpc/h, where the normalization of the power spectrum to the observed cluster abundance appears most appropriate. In that case, the correlation strength changes by less than a factor of <~ 2 when Omega_0 varies between 0.3 and 1, quite independent of the value of Omega_Lambda. For Omega_0 <~ 0.3, the correlation strength increases with decreasing Omega_0, and it scales approximately linearly with the Hubble constant h.Comment: revised version, accepted by MNRA

    The lens parallax method: determining redshifts of faint blue galaxies through gravitational lensing

    Get PDF
    We propose a new technique, which we call the lens parallax method, to determine simultaneously the redshift distribution of the faint blue galaxies and the mass distributions of foreground clusters of galaxies. The method is based on gravitational lensing and makes use of the following: (1) the amplitude of lensing-induced distortions of background galaxies increases with redshift; (2) the surface brightnesses of galaxies decrease steeply with redshift. The distortions of galaxy images due to lensing are thus expected to be inversely correlated with surface brightness, allowing us to obtain relative distances to galaxies as a function of surface brightness. If the redshifts of the brightest galaxies are measured, then the relative distance scale can be converted to mean galaxy redshifts as a function of surface brightness. Further, by comparing the angular sizes of lensed galaxies with those of similar galaxies in empty control fields, it is possible to break the so-called mass sheet degeneracy inherent to cluster mass reconstruction techniques which are based purely on image ellipticities. This allows an unambiguous determination of the surface density of a lensing cluster. We describe an iterative algorithm based on these ideas and present numerical simulations which show that the proposed techniques are feasible with a sample of ~ 10 rich clusters at moderate redshifts ~ 0.3-0.4 and an equal number of control fields. The numerical tests show that the method can be used to determine the redshifts of galaxies with an accuracy of dz ~ 0.1-0.2 at z ~ 1-1.7, and to measure the masses of lensing clusters to about 5% accuracy.Comment: 31 pages, uuencoded compressed postscript file containing 10 figures, to be published in the Sep. 20 issue of Ap
    • …
    corecore