OGLE-III, MCPS and HST VI obs. of LMC & SMC

We use archival HST observations to derive blending corrections and photometric transformations for two ground-based wide-area imaging surveys of the Magellanic Clouds. We show that these surveys are biased bright by up to ~0.1mag in the optical due to blending, and that the bias is a function of local stellar density.

We correct the LMC TRGB magnitudes from Jang & Lee (2017ApJ...835...28J) and use the geometric distance from Pietrzynski+ (2019Natur.567..200P) to obtain an absolute TRGB magnitude of M_F814W_=-3.97+/-0.046mag. Applying this calibration to the TRGB magnitudes from Freedman+ (2019ApJ...882...34F) in SN Ia hosts yields a value for the Hubble constant of H_0_=72.4+/-2.0km/s/Mpc for their TRGB+SNe Ia distance ladder. The difference in the TRGB calibration and the value of H_0_ derived here and by Freedman+ primarily results from their overestimate of the LMC extinction, caused by inconsistencies in their different sources of TRGB photometry for the Magellanic Clouds.