A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km s⁻¹ Mpc⁻¹ Uncertainty from the Hubble Space Telescope and the SH0ES Team

Abstract

We report observations from the Hubble Space Telescope (HST) of Cepheid variables in the host galaxies of 42 Type Ia supernovae (SNe Ia) used to calibrate the Hubble constant (H 0). These include the complete sample of all suitable SNe Ia discovered in the last four decades at redshift z ≤ 0.01, collected and calibrated from ≥1000 HST orbits, more than doubling the sample whose size limits the precision of the direct determination of H 0. The Cepheids are calibrated geometrically from Gaia EDR3 parallaxes, masers in NGC 4258 (here tripling that sample of Cepheids), and detached eclipsing binaries in the Large Magellanic Cloud. All Cepheids in these anchors and SN Ia hosts were measured with the same instrument (WFC3) and filters (F555W, F814W, F160W) to negate zero-point errors. We present multiple verifications of Cepheid photometry and six tests of background determinations that show Cepheid measurements are accurate in the presence of crowded backgrounds. The SNe Ia in these hosts calibrate the magnitude–redshift relation from the revised Pantheon+ compilation, accounting here for covariance between all SN data and with host properties and SN surveys matched throughout to negate systematics. We decrease the uncertainty in the local determination of H 0 to 1 km s−1 Mpc−1 including systematics. We present results for a comprehensive set of nearly 70 analysis variants to explore the sensitivity of H 0 to selections of anchors, SN surveys, redshift ranges, the treatment of Cepheid dust, metallicity, form of the period–luminosity relation, SN color, peculiar-velocity corrections, sample bifurcations, and simultaneous measurement of the expansion history. Our baseline result from the Cepheid–SN Ia sample is H 0 = 73.04 ± 1.04 km s−1 Mpc−1, which includes systematic uncertainties and lies near the median of all analysis variants. We demonstrate consistency with measures from HST of the TRGB between SN Ia hosts and NGC 4258, and include them simultaneously to yield 72.53 ± 0.99 km s−1 Mpc−1. The inclusion of high-redshift SNe Ia yields H 0 = 73.30 ± 1.04 km s−1 Mpc−1 and q 0 = −0.51 ± 0.024. We find a 5σ difference with the prediction of H 0 from Planck cosmic microwave background observations under ΛCDM, with no indication that the discrepancy arises from measurement uncertainties or analysis variations considered to date. The source of this now long-standing discrepancy between direct and cosmological routes to determining H 0 remains unknown.

A note on interacting holographic dark energy with a Hubble-scale cutoff

“…The six free parameters of the ΛCDM model are well constrained and are in agreement with cosmological observations [5], despite some tensions, e.g. the Hubble tension [5,6] (a recent review is [7]). The observed value of the vacuum energy is many orders of magnitude smaller than the theoretically calculated [8], leading to the so-called 'cosmological constant problem'.…”

Constraining spatial curvature with large-scale structure

“…We find that the mean value of H 0 , whether or not the SNIa sample is used, is lower than the local measurement of H 0 , using the distance-ladder technique. Given the lower resolution (roughly three time worse) than the CMB estimate, the tension with the latest measurement, H 0 = 73.04 ± 1.04 km/s/Mpc, from the Cepheid-SN sample of [82], is reduced to ∼ 2.85σ from the ∼ 4.8σ discrepancy with the Planck best fitting value. By adding the BAO prior we create a connection with the physics of the early Universe, via the sound horizon.…”

A step in the right direction? Analyzing the Wess Zumino Dark Radiation solution to the Hubble tension

“…Hereafter, in our figures the grey bands indicate the H 0 measurement by the SH0ES collaboration [2], while the light-blue bands indicate the combined results on S 8 from the combined analysis of KiDS-1000+BOSS+2dFLens from [35].…”

“…Thus its number and energy densities become exponentially suppressed compared to the massless species. In the end, the massless species continues evolving with a slightly increased number density and temperature due to the decay, while the massive species has become completely negligible 2 . Effectively, the model transitions smoothly from two relativistic species to one heated relativistic species.…”

“…The Hubble tension refers to the inconsistency between the locally measured Hubble value and the value as predicted from observations of the Cosmic Microwave Background (CMB). Despite the multitude of local measurements based on different anchors, standard candles, and analysis methodologies [2][3][4][5][6], as well as the multitude of CMB based measurements from Planck [7], ACT [8], and SPT [9], the tension between local and CMB-based inferences of the Hubble parameter remains at a level ranging around 4-5σ. See also [10][11][12] for some recent reviews.…”