Abstract
Context.The precise determination of the present-day expansion rate of the Universe, expressed through the Hubble constantH0, is one of the most pressing challenges in modern cosmology. Assuming flat ΛCDM,H0inference at high redshift using cosmic microwave background data fromPlanckdisagrees at the 4.4σlevel with measurements based on the local distance ladder made up of parallaxes, Cepheids, and Type Ia supernovae (SNe Ia), often referred to as Hubble tension. Independent cosmological-model-insensitive ways to inferH0are of critical importance.Aims.We apply an inverse distance ladder approach, combining strong-lensing time-delay distance measurements with SN Ia data. By themselves, SNe Ia are merely good indicators of relative distance, but by anchoring them to strong gravitational lenses we can obtain anH0measurement that is relatively insensitive to other cosmological parameters.Methods.A cosmological parameter estimate was performed for different cosmological background models, both for strong-lensing data alone and for the combined lensing + SNe Ia data sets.Results.The cosmological-model dependence of strong-lensingH0measurements is significantly mitigated through the inverse distance ladder. In combination with SN Ia data, the inferredH0consistently lies around 73–74 km s−1Mpc−1, regardless of the assumed cosmological background model. Our results agree closely with those from the local distance ladder, but there is a > 2σtension withPlanckresults, and a ∼1.5σdiscrepancy with results from an inverse distance ladder includingPlanck, baryon acoustic oscillations, and SNe Ia. Future strong-lensing distance measurements will reduce the uncertainties inH0from our inverse distance ladder.
Highlights
Ever since Georges Lemaître and Edwin Hubble discovered that our Universe is expanding (Lemaître 1927, 1931; Hubble 1929), astronomers have sought to measure the Hubble constant H0 that characterises the present-day expansion rate
The value of H0 inferred from the cosmic microwave background (CMB) depends on the background cosmology, and the 4.4σ tension between the Planck and SH0ES measurements refers to a standard flat ΛCDM cosmology with a spatially flat Universe consisting of cold dark matter and a dark energy that is described by the cosmological constant Λ
By anchoring the SN distance scale using distances measured from baryon acoustic oscillations (BAO), Macaulay et al (2019) measured an H0 from the Dark Energy Survey consistent with that provided by the Planck Collaboration VI (2018) and that does not depend much on cosmological models, the inference of H0 is strongly affected by the assumptions of the size of the sound horizon (Aylor et al 2019)
Summary
Ever since Georges Lemaître and Edwin Hubble discovered that our Universe is expanding (Lemaître 1927, 1931; Hubble 1929), astronomers have sought to measure the Hubble constant H0 that characterises the present-day expansion rate. The value of H0 inferred from the CMB depends on the background cosmology, and the 4.4σ tension between the Planck and SH0ES measurements refers to a standard flat ΛCDM cosmology with a spatially flat Universe consisting of cold dark matter and a dark energy that is described by the cosmological constant Λ. By anchoring the SN distance scale using distances measured from baryon acoustic oscillations (BAO), Macaulay et al (2019) measured an H0 from the Dark Energy Survey consistent with that provided by the Planck Collaboration VI (2018) and that does not depend much on cosmological models, the inference of H0 is strongly affected by the assumptions of the size of the sound horizon (Aylor et al 2019). Probability distributions, with 68% credibility intervals given by the 16th and 84th percentiles
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