H0 revisited

I reanalyse the Riess et al. (hereafter R11) Cepheid data using the revised geometric maser distance to NGC 4258 of Humphreys et al. (hereafter H13). I explore different outlier rejection criteria designed to give a reduced chi(2) of unity and compare the results with the R11 rejection algorithm, which produces a reduced chi(2) that is substantially less than unity and, in some cases, leads to underestimates of the errors on parameters. I show that there are sub-luminous low-metallicity Cepheids in the R11 sample that skew the global fits of the period-luminosity relation. This has a small but non-negligible impact on the global fits using NGC 4258 as a distance scale anchor, but adds a poorly constrained source of systematic error when using the Large Magellanic Cloud as an anchor. I also show that the small Milky Way Cepheid sample with accurate parallax measurements leads to a distance to NGC 4258 that is in tension with the maser distance. I conclude that H-0 based on the NGC 4258 maser distance is H-0 = 70.6 +/- 3.3 km s(-1) Mpc(-1), compatible within 1 Sigma with the recent determination from Planck for the base six-parameter Lambda cold dark matter cosmology. If the H-band period-luminosity relation is assumed to be independent of metallicity and the three distance anchors are combined, I find H-0 = 72.5 +/- 2.5 km s(-1) Mpc(-1), which differs by 1.9 Sigma from the Planck value. The differences between the Planck results and these estimates of H-0 are not large enough to provide compelling evidence for new physics at this stage.