# Consistent Calibration of the Tip of the Red Giant Branch in the Large Magellanic Cloud on the Hubble Space Telescope Photometric System and a Re-determination of the Hubble Constant

## TL;DR

This paper calibrates the Tip of the Red Giant Branch in the Large Magellanic Cloud using Hubble Space Telescope data, corrects for blending biases, and refines the measurement of the Hubble constant to 72.4 km/s/Mpc.

## Contribution

It provides a consistent TRGB calibration on the HST system and revises the Hubble constant by addressing previous extinction and blending biases.

## Key findings

- TRGB calibration magnitude: M_F814W=-3.97±0.046 mag
- Hubble constant: H_0=72.4±2.0 km/s/Mpc
- Lower LMC extinction estimate aligns with independent reddening maps

## Abstract

We present a calibration of the Tip of the Red Giant Branch (TRGB) in the Large Magellanic Cloud (LMC) on the HST/ACS F814W system. 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 ~0.1 mag 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 (2017) and use the geometric distance from Pietrzynski et al. (2019) to obtain an absolute TRGB magnitude of M_F814W=-3.97+/-0.046 mag. Applying this calibration to the TRGB magnitudes from Freedman et al. (2019) in SN Ia hosts yields a value for the Hubble constant of H_0=72.4+/-2.0 km/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 et al. (2019) primarily results from their overestimate of the LMC extinction, caused by inconsistencies in their different sources of TRGB photometry for the Magellanic Clouds. Using the same source of photometry (OGLE) for both Clouds and applying the aforementioned corrections yields a value for the LMC I-band TRGB extinction that is lower by 0.06 mag, consistent with independent OGLE reddening maps used by us and by Jang & Lee (2017) to calibrate TRGB and determine H_0.