An Improved Distance to NGC 4258 and its Implications for the Hubble Constant. (arXiv:1908.05625v1 [astro-ph.GA])

An Improved Distance to NGC 4258 and its Implications for the Hubble Constant. (arXiv:1908.05625v1 [astro-ph.GA])
<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:+Pesce_D/0/1/0/all/0/1">D. W. Pesce</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Riess_A/0/1/0/all/0/1">A. G. Riess</a>

NGC 4258 is a critical galaxy for establishing the extragalactic distance
scale and estimating the Hubble constant (Ho). Water masers in the nucleus of
the galaxy orbit about its supermassive black hole, and VLBI observations of
their positions, velocities and accelerations can be modeled to give a
geometric estimate of the angular-diameter distance to the galaxy. We have
improved the technique to obtain model parameter values, reducing both
statistical and systematic uncertainties compared to previous analyses. We find
the distance to NGC 4258 to be 7.58 +/- 0.08 (stat.) +/- 0.08 (sys.) Mpc. Using
this as the sole source of calibration of the Cepheid-SN Ia distance ladder
results in Ho = 72.0 +/- 1.9 km/s/Mpc, and in concert with geometric distances
from Milky Way parallaxes and detached eclipsing binaries in the LMC we find Ho
= 73.5 +/- 1.4 km/s/Mpc. The improved distance to NGC 4258 also provides a new
calibration of the Tip of the Red Giant Branch of M_{F814W} = -4.01 +/- 0.04$
mag, with reduced systematic errors for the determination of Ho compared to the
LMC-based calibration, because it is measured on the same HST photometric
system and through similarly low extinction as SN Ia host halos. The result is
Ho = 71.1 +/- 1.9 km/s/Mpc, in good agreement with the result from the Cepheid
route, and there is no difference in Ho when using the same calibration from
NGC 4258 and same SN Ia Hubble diagram intercept to start and end both distance
ladders.

NGC 4258 is a critical galaxy for establishing the extragalactic distance
scale and estimating the Hubble constant (Ho). Water masers in the nucleus of
the galaxy orbit about its supermassive black hole, and VLBI observations of
their positions, velocities and accelerations can be modeled to give a
geometric estimate of the angular-diameter distance to the galaxy. We have
improved the technique to obtain model parameter values, reducing both
statistical and systematic uncertainties compared to previous analyses. We find
the distance to NGC 4258 to be 7.58 +/- 0.08 (stat.) +/- 0.08 (sys.) Mpc. Using
this as the sole source of calibration of the Cepheid-SN Ia distance ladder
results in Ho = 72.0 +/- 1.9 km/s/Mpc, and in concert with geometric distances
from Milky Way parallaxes and detached eclipsing binaries in the LMC we find Ho
= 73.5 +/- 1.4 km/s/Mpc. The improved distance to NGC 4258 also provides a new
calibration of the Tip of the Red Giant Branch of M_{F814W} = -4.01 +/- 0.04$
mag, with reduced systematic errors for the determination of Ho compared to the
LMC-based calibration, because it is measured on the same HST photometric
system and through similarly low extinction as SN Ia host halos. The result is
Ho = 71.1 +/- 1.9 km/s/Mpc, in good agreement with the result from the Cepheid
route, and there is no difference in Ho when using the same calibration from
NGC 4258 and same SN Ia Hubble diagram intercept to start and end both distance
ladders.

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