http://arxiv.org/abs/2210.10688
When Type Ia supernovae are used to infer cosmological parameters, their luminosities are compared to those from a homogeneous cosmology. In this note we propose a test to examine to what degree SN Ia have been observed on lines of sight where the average matter density is \textit{not} representative of the homogeneous background. We use a modification to the Tripp estimator to explicitly de-lens SN Ia magnitudes, and show that it reduces scatter. We apply our test to the Pantheon SN Ia compilation, and find two redshift bins which indicate a moderate bias to over-density at $\sim 2\sigma$. Using our revised estimator, the effect on cosmological parameters from Pantheon in $\Lambda$CDM is however small with a change in mean value from $\Omega_{\rm m} = 0.317 \pm 0.027$ (baseline) to $\Omega_{\rm m} = 0.312 \pm 0.025$ (de-lensed). For the Flat $w$CDM case it is $\Omega_{\rm m} = 0.332 \pm 0.049$ and $w = -1.16 \pm 0.16$ (baseline) versus $\Omega_{\rm m} = 0.316 \pm 0.048$ and $w = -1.12 \pm 0.15$ (de-lensed). The change is larger if maximum likelihood values are used. We note that the effect of lensing on cosmological parameters may be larger for future high-z surveys.
P. Shah, P. Lemos and O. Lahav
Thu, 20 Oct 22
4/74
Comments: 4 pages, 3 figures. Submitted to MNRAS
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