# The Carnegie Chicago Hubble Program VI: Tip of the Red Giant Branch Distances to M66 and M96 of the Leo I Group

## TL;DR

This study accurately measures the distances to galaxies M66 and M96 in the Leo I Group using the Tip of the Red Giant Branch method with Hubble Space Telescope data, refining cosmic distance estimates.

## Contribution

It provides new TRGB-based distance measurements to M66 and M96, utilizing stellar halos and a recent LMC calibration for improved accuracy.

## Key findings

- Distances to M66 and M96 are precisely determined.
- The TRGB method effectively minimizes reddening and crowding effects.
- Results support improved calibration of cosmic distance scale.

## Abstract

We determine the distances to the Type Ia Supernova host galaxies M66 (NGC 3627) and M96 (NGC 3368) of the Leo I Group using the Tip of the Red Giant Branch (TRGB) method. We target the stellar halos of these galaxies using the Hubble Space Telescope ACS/WFC in the F606W and F814W bandpasses. By pointing to the stellar halos we sample RGB stars predominantly of Population II, minimize host-galaxy reddening, and significantly reduce the effects of source crowding. Our absolute calibration of the I-band TRGB is based on a recent detached eclipsing binary distance to the Large Magellanic Cloud. With this geometric zero point in hand, we find for M66 and M96, respectively, true distance moduli $ {\mu}_0 = 30.23 \pm 0.04\text{ (stat)} \pm 0.06\text{ (sys)} $ mag and $ {\mu}_0 = 30.29 \pm 0.02\text{ (stat)} \pm 0.06\text{ (sys)} $ mag.