A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc 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 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 zeropoint errors.We present multiple verifications of Cepheid photometry and six tests of background determinations that show Cepheid measurements are accurate in the presence of crowding. The SNe Ia in these hosts calibrate the magnitude-redshift relation from the revised Pantheon+ compilation, accounting here for covariance between all SNe 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 CMB 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 the Hubble constant remains unknown.

Cosmological Results from the RAISIN Survey: Using Type Ia Supernovae in the Near Infrared as a Novel Path to Measure the Dark Energy Equation of State

“…2021; Riess et al 2021) and take the agnostic approach of giving all available distances as originally provided equal weight. We use Cepheid distances from Riess et al (2021) for five SNe: 2006D, 2007A, 2009Y, 2012ht, and 2015F.…”

“…2021; Riess et al 2021) and take the agnostic approach of giving all available distances as originally provided equal weight. We use Cepheid distances from Riess et al (2021) for five SNe: 2006D, 2007A, 2009Y, 2012ht, and 2015F. We use the mean of available Cepheid and TRGB distances for three SNe: 2007af (Freedman et al 2019;Riess et al 2021), 2007sr (Freedman et al 2019Anand et al 2021;Riess et al 2021), and 2012fr (Freedman et al 2019;Anand et al 2021;Riess et al 2021).…”

“…We use Cepheid distances from Riess et al (2021) for five SNe: 2006D, 2007A, 2009Y, 2012ht, and 2015F. We use the mean of available Cepheid and TRGB distances for three SNe: 2007af (Freedman et al 2019;Riess et al 2021), 2007sr (Freedman et al 2019Anand et al 2021;Riess et al 2021), and 2012fr (Freedman et al 2019;Anand et al 2021;Riess et al 2021). Finally, we use the mean TRGB distances for two SNe from Freedman et al (2019) and Anand et al (2021), SNe 2007on and 2011iv, which are in the same host galaxy of NGC 1404.…”

“…We use these Cepheid and TRGB distances to calibrate the SN luminosity of the CSP and RAISIN samples following the method of Riess et al (2021). If we include SNe 2007on and 2011iv in our H 0 measurement, we measure H 0 = 77.2 ± 2.3 km s −1 Mpc −1 from Cepheid+TRGB and H 0 = 76.5 ± 2.8 km s −1 Mpc −1 from TRGB alone.…”

“…Low-z NIR data have recently been used to demonstrate a significant relationship between SN Ia distance residuals and the mass of the SN Ia host galaxy (Ponder et al 2021;Uddin et al 2020), which was discovered at optical wavelengths (Kelly et al 2010;Lampeitl et al 2010;Sullivan et al 2010), although Johansson et al (2021) found mildly conflicting results with no evidence for a mass-step in the JH bands and ∼2-σ evidence for a step in the Y band. Burns et al (2018) and Dhawan et al (2018) used NIR data to measure the Hubble constant, H 0 , using this new SN Ia wavelength range to provide additional evidence for tension between Cepheid+SN distance ladder measurements of H 0 (e.g., Riess et al 2021) and the cosmic microwave background (CMB; Planck Collaboration et al 2018).…”