Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

Wide-separation lensed QSOs measure the mass function and evolution of massive galaxy clusters, in a similar way to the cluster mass function deduced from X-ray-selected samples or statistical measurements of the Sunyaev-Zeldovich effect. We compute probabilities of strong lensing of QSOs by galaxy clusters in dark energy cosmologies using semianalytical modelling and explore the sensitivity of the method to various input parameters and assumptions. We highlight the importance of considering both the variation of halo properties with mass, redshift and cosmology and the effect of cosmic scatter in halo concentration. We then investigate the extent to which observational surveys for wide-separation lensed QSOs may be used to measure cosmological parameters such as the fractional matter density Omega_M, the rms linear density fluctuation in spheres of 8 Mpc/h, sigma_8, and the dark energy equation of state parameter w. We find that wide-separation lensed QSOs can measure sigma_8 and Omega_M in an equivalent manner to other methods such as cluster abundance studies and cosmic shear measurements. In assessing whether lensing statistics can distinguish between values of w, we conclude that at present the uncertainty in the calibration of sigma_8 in quintessence models dominates the conclusions reached. Nonetheless, lensing searches based on current QSO surveys such as the Two-degree Field and the Sloan Digital Sky Survey with 10^4-10^5 QSOs should detect systems with angular separations greater than 5'' and hence can provide an important test of the standard cosmological model that is complementary to measurements of cosmic microwave background anisotropies.

Abstract:

We describe different methods for estimating the bispectrum of cosmic microwave background data. In particular, we construct a minimum-variance estimator for the flat-sky limit and compare results with previously studied frequentist methods. Application to the MAXIMA data set shows consistency with primordial Gaussianity. Weak quadratic non-Gaussianity is characterized by a tunable parameter fNL, corresponding to non-Gaussianity at a level of ∼10-5 fNL (the ratio of non-Gaussian to Gaussian terms), and we find limits of fNL = 1500 ± 950 for the minimum-variance estimator and fNL = 2700 ± 1650 for the usual frequentist estimator. These are the tightest limits on primordial non-Gaussianity, which include the full effects of the radiation transfer function.

Abstract:

Using mean relative peculiar velocity measurements for pairs of galaxies, we estimate the cosmological density parameter $\Omega_m$ and the amplitude of density fluctuations $\sigma_8$. Our results suggest that our statistic is a robust and reproducible measure of the mean pairwise velocity and thereby the $\Omega_m$ parameter. We get $\Omega_m = 0.30^{+0.17}_{-0.07}$ and $\sigma_8 = 1.13^{+0.22}_{-0.23}$. These estimates do not depend on prior assumptions on the adiabaticity of the initial density fluctuations, the ionization history, or the values of other cosmological parameters.

Abstract:

We have used composite spectra generated from more than 22000 QSOs observed in the course of the 2dF and 6dF QSO Redshift Surveys to investigate the relationship between the velocity width of emission lines and QSO luminosity. We find that the velocity width of the broad emission lines Hbeta, Hgamma, MgII, CIII] and CIV are correlated with the continuum luminosity, with a significance of more than 99 per cent. Of the major narrow emission lines ([OIII] 5007, [OII] 3727, NeIII 3870 and NeV 3426) only [OIII] exhibits a significant correlation between line width and luminosity. Assuming that the gas is moving in Keplerian orbits and that the radius of the broad line region is related to the QSO continuum luminosity, we use the velocity widths of the broad lines to derive average black hole masses for the QSOs contributing to the composite spectra. The resultant QSO mass-luminosity relationship is consistent with M ~ L^0.97+-0.16. We find that the correlation between line width and redshift, if present, must be weak, and only CIV shows significant evidence of evolution. This enables us to constrain the redshift evolution of the black hole mass-luminosity ratio to be ~(1+z)^beta with beta ~< 1, much less than the ~(1+z)^3 evolution seen in QSO luminosity evolution. Assuming that the motion of the broad line region gas is Keplerian and that its radius depends on the QSO luminosity, our models indicate that the observed weak redshift dependence is too small for the observed QSO luminosity function to be due to the evolution of a single long-lived population of sources.