The ACS LCID project IV: detection of the RGB bump in isolated galaxies of the Local Group

TL;DR

This study detects the RGB bump in isolated Local Group dwarf galaxies using a novel comparison method with theoretical models, finding close agreement and reducing previous discrepancies seen in globular clusters.

Contribution

Introduces a new analysis technique for measuring the RGB bump in complex stellar systems, improving the comparison between observations and theoretical predictions.

Findings

The difference between observed and predicted Delta_vhbb is +0.13 +/- 0.14 mag.

Good agreement between observed and theoretical R_bump values.

Red giant branch bump detection supports the accuracy of stellar evolution models.

Abstract

We report the detection and analysis of the red giant branch luminosity function bump in a sample of isolated dwarf galaxies in the Local Group. We have designed a new analysis approach comparing the observed color-magnitude diagrams with theoretical best-fit color-magnitude diagrams derived from precise estimates of the star formation histories of each galaxy. This analysis is based on studying the difference between the V-magnitude of the RGB bump and the horizontal branch at the level of the RR Lyrae instability strip (Delta_vhbb) and we discuss here a technique for reliably measuring this quantity in complex stellar systems. By using this approach, we find that the difference between the observed and predicted values of Delta_vhbb is +0.13 +/- 0.14 mag. This is smaller, by about a factor of two, than the well-known discrepancy between theory and observation at low metallicity commonly derived for Galactic globular clusters. This result is confirmed by a comparison between the adopted theoretical framework and empirical estimates of the Delta_vhbb parameter for both a large database of Galactic globular clusters and for four other dSph galaxies for which this estimate is available in the literature. We also investigate the strength of the red giant branch bump feature (R_bump), and find very good agreement between the observed and theoretically predicted R_bump values. This agreement supports the reliability of the evolutionary lifetimes predicted by theoretical models of the evolution of low-mass stars.