A Sizable Discrepancy in Ground-Based JAGB Distances to Nearby Galaxies

TL;DR

This study finds a significant discrepancy between ground-based JAGB and space-based TRGB distance measurements to nearby galaxies, raising concerns about potential systematic errors affecting the JAGB method's reliability for precise cosmological measurements.

Contribution

It highlights a notable offset between ground-based JAGB and space-based TRGB distances, suggesting possible ground-based observational systematics affecting the JAGB method.

Findings

HST TRGB distances are systematically larger than ground-based JAGB distances.

The discrepancy is approximately 0.17 mag, or about 9% in distance.

Further high-resolution observations are needed to resolve the systematic differences.

Abstract

Recently, Freedman et al. (2024) report agreement of distances derived from the Tip of the Red Giant Branch (TRGB) and the J-Region Asymptotic Giant Branch (JAGB) at the 1$\%$ level for both nearby galaxies with ground-based imaging (0.5-4 Mpc) as well distant galaxies with JWST imaging (7-23 Mpc). Here we compare the same ground-based JAGB distances to uniformly reduced space-based optical TRGB distances from the Hubble Space Telescope (HST). We uncover a significant offset between these two distance scales of $\Delta\mu$ = 0.17 $\pm$ 0.04 (stat) $\pm$ 0.06 (sys) mag (9$\%$ in distance), with the HST TRGB distances being further. Inspections of the HST color-magnitude diagrams make a compelling case that the issue lies in the underlying JAGB distances. The source of the disagreement may lie with the lower resolution or photometric calibration of the ground-based near-infrared data, a contrast to the general agreement found between JWST JAGB and other space-based, second-rung distance indicators (Cepheids, Miras, TRGB) presented within Riess et al. (2024). High-resolution, near-infrared observations from an ongoing HST program will enable the simultaneous measurement of Cepheid, JAGB, and TRGB distances in four of these nearby galaxies and allow us to investigate whether the discrepancy noted here is due to ground-based observational systematics, or something intrinsic to the JAGB method relevant for this particular sample. A resolution of this discrepancy is required if the JAGB is to be used to determine a highly precise local value of the Hubble constant.