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

Abstract

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 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 Lightcurve Analysis (JLA) supernova catalogue. When we impose only that the intrinsic dispersion in magnitudes is independent of redshift, we find σ 8 = 0.44 +0.63 −0.44 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 σ 8 . We note that the degeneracy between intrinsic dispersion and the effects of σ 8 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 σ 8 = 1.07 +0.50 −0.76 .

The impact of microlensing on the standardization of strongly lensed Type Ia supernovae

“…In Figure 4, we show how the microlensing scatter σML varies with κ, γ and s, across a range of times t. We find that there is a region of parameter space where the light curves from GLSNe Ia are standardisable as the scatter due to microlensing is comparable to the typical intrinsic dispersion for a SN Ia after standardisation (Betoule et al 2014;Macaulay et al 2017). Therefore, with the correct lensing configuration, it is possible to infer the unlensed magnitude of the source SN Ia.…”

Bias and scatter in the Hubble diagram from cosmological large-scale structure

“…This PDF has already been studied by various authors in the past, e.g. [23][24][25][26], but we present the first fully non-perturbative and relativistic calculation of D L (z). For z 1 the peak of the distribution is shifted by 1% while the shift of the mean, shown in the bottom panel of Fig.…”

Limits on Stellar-Mass Compact Objects as Dark Matter from Gravitational Lensing of Type Ia Supernovae

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