Brightest stars of irregular and low-massive spiral galaxies

Abstract

A search for a correlation between the luminosities of the brightest stars and luminosities of their host galaxies was carried out on archived Hubble Space Telescope (HST) F 606W or F 555W (V ) and F 814W (I) images of about 150 nearby galaxies. The sample contains only galaxies with on-going star formation (SF) and with known distances we derived with the TRGB-method. We correlated the average absolute luminosities of the three brightest blue and the three brightest red stars with the luminosity of a host. We found a linear relation for both the blue and the red stars in irregular and low-mass spiral galaxies. Their scatters are sufficiently small (0 .m 4) to make this relations useful for distance determination for low-mass galaxies. We found that all 31 dwarf galaxies (M B >−13 m ) in our sample lack bright stars (M V (BS) < −7 .m 0), probably due to the physical conditions that prevent their birth. For galaxies with higher luminosity in the range −18 m <M B <−13 m , there is an asymmetry in the distribution of the number of galaxies relative to the linear dependence, indicating an increase in the fraction of galaxies with bright stars.