Mathematical Underpinnings of the Multi-Wavelength Structure of the TRGB

TL;DR

This paper develops a mathematically self-consistent framework for calibrating the tip of the red giant branch (TRGB) method across optical and near-infrared wavelengths, improving distance measurements to nearby galaxies.

Contribution

It introduces a unified mathematical approach for multi-wavelength TRGB calibration and a method to determine reddening and extinction directly from TRGB data.

Findings

Optical and near-infrared calibrations are mathematically self-consistent.

The method allows for reddening estimation directly from TRGB stars.

Reduces systematic uncertainty in galaxy distance measurements.

Abstract

We consider the application of the tip of the red giant branch (TRGB) in the optical and in the near infrared for the determination of distances to nearby galaxies. We analyze ACS VI (F555W & F814W) data and self-consistently cross-calibrate WFC3-IR JH (F110W & F120W) data using and absolute magnitude calibration of M_I = -4.05 mag as determined in the LMC using detached eclipsing binary star geometric parallaxes. We demonstrate how the optical and near-infrared calibrations of the TRGB method are mathematically self-consistent, and illustrate the mathematical basis and relations amongst these multi-wavelength calibrations. We go on to present a method for determining the reddening, extinction and the true modulus to the host galaxy using multi-wavelength data. The power of the method is that with high-precision data, the reddening can be determined using the TRGB stars themselves, and decreases the systematic (albeit generally small) uncertainty in distance due to reddening for these halo stars.