Journal Article

The effects of velocities and lensing on moments of the Hubble diagram

E. Macaulay, T. M. Davis, D. Scovacricchi, D. Bacon, T. Collett and R. C. Nichol

in Monthly Notices of the Royal Astronomical Society

Published on behalf of Royal Astronomical Society

Volume 467, issue 1, pages 259-272
ISSN: 0035-8711
Published online December 2016 | e-ISSN: 1365-2966 | DOI:
The effects of velocities and lensing on moments of the Hubble diagram

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We consider the dispersion on the supernova distance–redshift relation due to peculiar velocities and gravitational lensing, and the sensitivity of these effects to the amplitude of the matter power spectrum. We use the Method-of-the-Moments (MeMo) lensing likelihood developed by Quartin et al., which accounts for the characteristic non-Gaussian distribution caused by lensing magnification with measurements of the first four central moments of the distribution of magnitudes. We build on the MeMo likelihood by including the effects of peculiar velocities directly into the model for the moments. In order to measure the moments from sparse numbers of supernovae, we take a new approach using Kernel density estimation to estimate the underlying probability density function of the magnitude residuals. We also describe a bootstrap re-sampling approach to estimate the data covariance matrix. We then apply the method to the joint light-curve analysis (JLA) supernova catalogue. When we impose only that the intrinsic dispersion in magnitudes is independent of redshift, we find [math] at the one standard deviation level, although we note that in tests on simulations, this model tends to overestimate the magnitude of the intrinsic dispersion, and underestimate σ8. We note that the degeneracy between intrinsic dispersion and the effects of σ8 is more pronounced when lensing and velocity effects are considered simultaneously, due to a cancellation of redshift dependence when both effects are included. Keeping the model of the intrinsic dispersion fixed as a Gaussian distribution of width 0.14 mag, we find [math].

Keywords: galaxies: kinematics and dynamics; galaxies: statistics; cosmology: observations; cosmology: theory; large-scale structure of universe

Journal Article.  9027 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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