The Megamaser Cosmology Project. XIII. Combined Hubble constant constraints

Understand

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 $H_0 = 73.9 \pm 3.0$ 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.