The Tip of the Red Giant Branch Distances to Type Ia Supernova Host Galaxies. IV. Color Dependence and Zero-Point Calibration

TL;DR

This paper refines the Tip of the Red Giant Branch (TRGB) distance calibration by introducing a color-corrected magnitude, achieving higher precision and comparing it with stellar models, to improve extragalactic distance measurements.

Contribution

A new TRGB calibration using a color-dependent magnitude and two distance anchors, reducing uncertainties and providing a revised zero-point for better distance estimates.

Findings

The zero-point of the TRGB at fiducial metallicity is determined with ~2x smaller uncertainty.

The empirical calibration shows significant discrepancies with theoretical models at red colors.

The revised calibration is provided in multiple magnitude systems for future use.

Abstract

We present a revised TRGB calibration, accurate to 2.7% of distance. A modified TRGB magnitude corrected for the color dependence of the TRGB, the QT magnitude, is introduced for better measurement of the TRGB. We determine the color-magnitude relation of the TRGB from photometry of deep images of HST/ACS fields around eight nearby galaxies. The zero-point of the TRGB at the fiducial metallicity ([Fe/H]=-1.6 ((V-I)_{0,TRGB}=1.5)) is obtained from photometry of two distance anchors, NGC 4258 (M106) and the LMC, to which precise geometric distances are known: M_{QT,TRGB}=-4.023+-0.073 mag from NGC 4258 and M_{QT,TRGB}=-4.004+-0.096 mag from the LMC. A weighted mean of the two zero-points is M_{QT,TRGB}=-4.016+-0.058 mag. Quoted uncertainty is ~2 times smaller than those of the previous calibrations. We compare the empirical TRGB calibration derived in this study with theoretical stellar models, finding that there are significant discrepancies, especially for red color ((F606W-F814W)_0 > 2.5). We provide the revised TRGB calibration in several magnitude systems for future studies.