Cluster Cepheids with High Precision Gaia Parallaxes, Low Zeropoint Uncertainties, and Hubble Space Telescope Photometry. (arXiv:2208.01045v1 [astro-ph.CO])

Cluster Cepheids with High Precision Gaia Parallaxes, Low Zeropoint Uncertainties, and Hubble Space Telescope Photometry. (arXiv:2208.01045v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Riess_A/0/1/0/all/0/1">Adam G. Riess</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Breuval_L/0/1/0/all/0/1">Louise Breuval</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yuan_W/0/1/0/all/0/1">Wenlong Yuan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Casertano_S/0/1/0/all/0/1">Stefano Casertano</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Macri_L/0/1/0/all/0/1">Lucas M.~Macri</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Scolnic_D/0/1/0/all/0/1">Dan Scolnic</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cantat_Gaudin_T/0/1/0/all/0/1">Tristan Cantat-Gaudin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Anderson_R/0/1/0/all/0/1">Richard I. Anderson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reyes_M/0/1/0/all/0/1">Mauricio Cruz Reyes</a>

We present HST photometry of 17 Cepheids in open clusters and their mean
parallaxes from Gaia EDR3. These parallaxes are more precise than those from
individual Cepheids (G<8 mag) previously used to measure the Hubble constant
because they are derived from an average of >300 stars per cluster. Cluster
parallaxes also have smaller systematic uncertainty because their stars lie in
the range (G>13 mag) where the Gaia parallax calibration is most comprehensive.
Cepheid photometry employed in the period–luminosity relation was measured
using the same instrument(WFC3) and filters(F555W,F814W,F160W) as extragalactic
Cepheids in SNIa hosts. We find no evidence of residual parallax offset in this
magnitude range, zp=-3+/-4 muas, consistent with Lindegren:2021b and most
studies. The Cepheid luminosity (P=10d, solar-metallicity) in the HST
near-infrared, Wesenheit system derived from the cluster sample is
M_{H,1}^W=-5.902+/-0.025 and -5.890+/-0.018 mag with or without simultaneous
determination of a parallax offset, respectively. These results are similar to
measurements from field Cepheids, confirming the accuracy of the Gaia
parallaxes over a broad range of magnitudes. The SH0ES distance ladder
calibrated solely from this sample gives H_0=72.8+/-1.3 and H_0=73.2+/-1.1
km/s/Mpc with or without offset marginalization; combined with all anchors we
find H_0=73.01+/-0.99 and 73.15+/-0.97, respectively, a 5% or 7% reduction in
the uncertainty and a 5.3 sigma Hubble Tension relative to Planck+LambdaCDM. It
appears increasingly difficult to reconcile two of the best measured cosmic
scales, parallaxes from Gaia and the angular size of the acoustic scale of the
CMB, using the simplest form of LambdaCDM to join the two.

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