Extragalactic Stellar Astronomy with the Brightest Stars in the Universe

TL;DR

This paper reviews the use of supergiant stars as tools for extragalactic astronomy, highlighting recent spectral analysis techniques and introducing a new spectroscopic distance measurement method, the FGLR, for galaxies beyond the Local Group.

Contribution

It presents a new spectroscopic method, the flux weighted gravity - luminosity relationship (FGLR), for accurate extragalactic distance measurement using supergiants.

Findings

Successful spectral analysis of supergiants in distant galaxies.

Development of the FGLR method for distance determination.

Future prospects with next-generation telescopes.

Abstract

A supergiants are objects in transition from the blue to the red (and vice versa) in the uppermost HRD. They are the intrinsically brightest "normal" stars at visual light with absolute visual magnitudes up to -9. They are ideal to study young stellar populations in galaxies beyond the Local Group to determine chemical composition and evolution, interstellar extinction, reddening laws and distances. We discuss most recent results on the quantitative spectral analysis of such objects in galaxies beyond the Local Group based on medium and low resolution spectra obtained with the ESO VLT and Keck. We describe the analysis method including the determination of metallicity and metallicity gradients. A new method to measure accurate extragalactic distances based on the stellar gravities and effective temperatures is presented, the flux weighted gravity - luminosity relationship (FGLR). The FGLR is a purely spectroscopic method, which overcomes the untertainties introduced by interstellar extinction and variations of metallicity, which plague all photometric stellar distance determination methods. We discuss the perspectives of future work using the giant ground-based telescopes of the next generation such as the TMT, the GMT and the E-ELT.