Luminosities of the Brightest Blue Stars in 30 Dwarf Galaxies

Abstract

The stellar and integral photometry of 30 irregular dwarf galaxies was performed in the \(F606W\) (\(V\)) and \(F814W\) (\(I\)) filters based on archival images from the Hubble Space Telescope. Distances were determined for 12 galaxies using the TRGB method. Branches of blue supergiants were identified on the plotted Hertzsprung–Russell diagrams, and the average luminosities of the three brightest stars were calculated. The color indices \((V-I)\) and luminosities of galaxies in the \(V\) and \(I\) filters were determined in circular apertures with the maximum radius \(\textrm{Rad}=50^{\prime\prime}\). A diagram of the dependence between the luminosities of galaxies and their brightest stars was developed, which shows that the luminosity of the brightest stars increases with increasing luminosity of the parent galaxies. A comparison of the dependence for 30 irregular galaxies with a similar one for 150 spiral and irregular galaxies, published by Tikhonov et al. in 2021, shows their similarity. This result confirms the hypothesis that the absence of bright massive stars in dwarf irregular galaxies cannot be explained by the small number of stars in these galaxies. Using the results of Hunter et al. (2019 and 2021), we developed a dependence between the luminosity of galaxies and the mass of the third-largest H I cloud of these galaxies. The presented correlation, as well as the well-known Larson correlation proposed in 1982, between the mass of molecular hydrogen clouds and the mass of stars born in them, give us reason to conclude that the dependence between the luminosity of galaxies and the brightest stars is a consequence of the correlation between the luminosity (mass) of galaxies and the average mass of the gaseous clouds of these galaxies.