The Megamaser Cosmology Project. XIII. Combined Hubble Constant Constraints

Abstract

We present a measurement of the Hubble constant made using geometric distance measurements to megamaser-hosting galaxies. We have applied an improved approach for fitting maser data and obtained better distance estimates for four galaxies previously published by the Megamaser Cosmology Project: UGC 3789, NGC 6264, NGC 6323, and NGC 5765b. Combining these updated distance measurements with those for the maser galaxies CGCG 074-064 and NGC 4258, and assuming a fixed velocity uncertainty of 250 km s −1 associated with peculiar motions, we constrain the Hubble constant to be H 0 = 73.9±3.0 km s −1 Mpc −1 independent of distance ladders and the cosmic microwave background. This best value relies solely on maser-based distance and velocity measurements, and it does not use any peculiar velocity corrections. Different approaches for correcting peculiar velocities do not modify H 0 by more than ±1σ, with the full range of best-fit Hubble constant values spanning 71.8-76.9 km s −1 Mpc −1 . We corroborate prior indications that the local value of H 0 exceeds the early-Universe value, with a confidence level varying from 95-99% for different treatments of the peculiar velocities.

Constraining early dark energy with large-scale structure

“…The EDE component is not detected here; a 68% confidence limit yields f EDE ¼ 0.025 þ0.0061 −0.025 , i.e., consistent with zero. The EDE value of H 0 is in 3.6σ tension with the SH0ES measurement (H 0 ¼ 74.03 AE 1.42 km=s=Mpc).ParameterΛCDM EDE ðn ¼ 3Þ lnð1010 A s Þ 3.043ð3.034Þ AE 0.014 3.047ð3.049Þ AE 0.014…”

“…The dark-shaded and light-shaded contours mark 68% and 95% confidence intervals, respectively. use the MONTE PYTHON implementation of this likelihood, after having corrected a non-negligible bug reported on GitHub, 10 which had not been fixed in the official code distribution at the time when this manuscript was finalized.…”

“…For instance, the Cepheids utilized for calibration of the cosmic distance ladder by SH0ES can be replaced with Miras, variable red giant stars, leading to H 0 ¼ 73.3 AE 3.9 km=s=Mpc [4], or traded for the "tip of the red giant branch" in the Hertzsprung-Russell diagram, which yields a somewhat lower value, H 0 ¼ 69.6 AE 1.9 km=s=Mpc [5]. Alternatively, local measurements can be performed in a variety of ways that are independent of the cosmic distance ladder-e.g., through the measurement of time delays in strongly lensed quasar systems, which yields H 0 ¼ 73.3 þ1.7 −1.8 km=s=Mpc [6], 2 through very long-baseline interferometry observations of water masers orbiting supermassive black holes, which yields H 0 ¼ 73.9 AE 3.0 km=s=Mpc [10], and through gravitational waves from merging binary neutron stars [11,12].…”

Geometry of numbers and dimensionality

“…The independent Megamaser Cosmology Project considers galaxies with disks of waterbearing molecular gas orbiting supermassive black holes at galaxy centers. Considering distance measurements to four galaxies, and combined with previous distance measurements of two other galaxies, the calculations produce a value for H0 of 73.9 km s -1 Mpc -1 [17] that is nearly identical to the SHoES estimate. The discrepancy between the early and late universe estimates of the Hubble constant has not yielded to any analysis and it has been termed a crisis in physics [18].…”

On the road to per cent accuracy IV: ReACT – computing the non-linear power spectrum beyond ΛCDM

“…Further, several mild tensions in cosmological parameters between late-time measurements and the CMB have been uncovered. In particular, there is a tension in the value of the Hubble parameter today, H 0 , (Efstathiou 2014;Zhang et al 2017;Riess et al 2019;Wong et al 2020;Lombriser 2020;Pesce et al 2020) and in the amplitude of density fluctuations, σ 8 , (Heymans et al 2013;Hildebrandt et al 2017;Abbott et al 2018) from direct measurement and E-mail:benjamin.bose@unige.ch inferred from extrapolating from the best fit CMB data (Ade et al 2016) (also see Lin & Ishak 2017).…”