Abstract
Abstract The time delay measured between the images of gravitationally lensed quasars probes a combination of the angular diameter distance to the source-lens system and the mass density profile of the lens. Observational campaigns to measure such systems have reported a determination of the Hubble parameter H 0 that shows significant tension with independent determination based on the cosmic microwave background (CMB) and large-scale structure (LSS). We show that lens mass models that exhibit a cored component, coexisting with a cusp, probe a degenerate direction in the lens model parameter space, being an approximate mass sheet transformation. This family of lens models has not been considered by the cosmographic analyses. Once added to the model, the cosmographic error budget should become dependent on stellar kinematics uncertainties. We propose that a core component coexisting with a cusp could bring the lensing measurements of H 0 into accordance with the CMB/LSS value.
Highlights
AND MAIN RESULTThere appears to be a tension between measurements of the Hubble parameter H0 based on the classic cosmic distance ladder method and measurements obtained through a fit of the standard ΛCDM model to the cosmic microwave background (CMB) or large scale structure (LSS) data (for a summary, see Verde et al (2019))
We show that lens mass models that exhibit a cored component, coexisting with a cusp, probe a degenerate direction in the lens model parameter space, being an approximate mass sheet transformation
This result is more than 4σ discrepant with the best fit ΛCDM value given by the Planck collaboration H0 = 67.36 ± 0.54 km/s/Mpc (Planck Collaboration et al (2018)), or with H0 measurements obtained from galaxy clustering and galaxy lensing data (Abbott et al 2018; Ivanov et al 2019; D’Amico et al 2019; Troster et al 2019), that are independent of but agree with the CMB result
Summary
There appears to be a tension between measurements of the Hubble parameter H0 based on the classic cosmic distance ladder method and measurements obtained through a fit of the standard ΛCDM model to the CMB or LSS data (for a summary, see Verde et al (2019)). As mentioned above, to solve the H0 tension we need an effect of no more than 10% in enclosed mass within θE Constraining this with stellar kinematics would not be trivial and would suffer from systematic uncertainties related to, e.g., the velocity anisotropy modelling. Kinematics modelling uncertainties would come to dominate the determination of H0, which should be revised (Kochanek (2019)) Perhaps another potential way to resolve the MSD would be to have multiple sources lensed by the same object, as is usually the case in lensing by galaxy clusters (Grillo et al 2018, 2020). It is worth pointing out that we are not aware of the presence of PL+core profiles in simulations In this sense, introducing them is an ad-hoc solution of the (cosmographic contribution to) the H0 tension. A we collect some formulae for profiles that could serve as λPL models
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