Extra-galactic distances with massive stars: the role of stellar variability in the case of M33

TL;DR

This paper investigates whether stellar variability affects the flux-weighted gravity luminosity relation (FGLR) distance measurements for M33, finding that variability has negligible impact, thus supporting FGLR's reliability as a distance indicator.

Contribution

The study demonstrates that stellar variability does not significantly bias FGLR-based distance estimates for M33, confirming its robustness against stellar variability systematics.

Findings

9 out of 22 BSGs showed variability with small amplitudes

Stellar variability has negligible effect on FGLR distance estimates

Supports FGLR as a reliable distance indicator for M33

Abstract

In modern cosmology, determining the Hubble constant (H0) using distance ladder to percent level and comparing with the results from Planck satellite can shed light on the nature of the dark energy, the physics of neutrino, and the curvature of the universe. Thanks to the endeavor of the SH0ES team, the uncertainty of the H0 has be dramatically reduced from 10% to 2.4%, with the promise to reach even 1% in the near future. In this regard, it is fundamentally important to beat and investigate the systematics. This is best be done with other independent good distance indicators. One of the promising method is the flux-weighted gravity luminosity relation (FGLR) of the blue supergiants. As the blue supergiants are the brightest objects in the galaxies, they can probe distance up to 10 Mpc, with negligible blending effects. While the FGLR method delivered distance in good agreement with other distance indicators, it has been shown that this method delivers larger distance in the case of M33 and NGC 55. Here we investigate whether the M33 distance estimate of FGLR suffers systematics from stellar variability. Using CFHT M33 monitoring data, we found 9 out of 22 BSGs showed variability during the course of 500 days, however with amplitudes as small as 0.05 magnitudes. This suggests that stellar variability plays negligible role in the FGLR distance determination.