The Megamaser Cosmology Project. XIII. Combined Hubble constant constraints. (arXiv:2001.09213v1 [astro-ph.CO])

The Megamaser Cosmology Project. XIII. Combined Hubble constant constraints. (arXiv:2001.09213v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Pesce_D/0/1/0/all/0/1">D. W. Pesce</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Braatz_J/0/1/0/all/0/1">J. A. Braatz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reid_M/0/1/0/all/0/1">M. J. Reid</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Riess_A/0/1/0/all/0/1">A. G. Riess</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Scolnic_D/0/1/0/all/0/1">D. Scolnic</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Condon_J/0/1/0/all/0/1">J. J. Condon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gao_F/0/1/0/all/0/1">F. Gao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Henkel_C/0/1/0/all/0/1">C. Henkel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Impellizzeri_C/0/1/0/all/0/1">C. M. V. Impellizzeri</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kuo_C/0/1/0/all/0/1">C. Y. Kuo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lo_K/0/1/0/all/0/1">K. Y. Lo</a>

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. Different
approaches for correcting peculiar velocities do not modify $H_0$ by more than
${pm}1{sigma}$, 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.

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. Different
approaches for correcting peculiar velocities do not modify $H_0$ by more than
${pm}1{sigma}$, 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.

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