The Evolved Red Stellar Contents of the Sculptor Group Galaxies NGC 55, NGC 300, and NGC 7793

Deep J, H, and K images are used to probe the evolved stellar contents in thecentral regions of the Sculptor group galaxies NGC55, NGC300, and NGC7793. Thebrightest stars are massive red supergiants (RSGs) with K ~ 15 - 15.5. The peakRSG brightness is constant to within ~0.5 mag in K, suggesting that NGC55,NGC300, and NGC7793 are at comparable distances. Comparisons with bright RSGsin the Magellanic Clouds indicate that the difference in distance modulus withrespect to the LMC is = 7.5. A rich population of asymptotic giant branch (AGB)stars, which isochrones indicate have ages between 0.1 and 10 Gyr, dominatesthe (K, J-K) color-magnitude diagram (CMD) of each galaxy. The detection ofsignificant numbers of AGB stars with ages near 10 Gyr indicates that the disksof these galaxies contain an underlying old population. The CMDs and luminosityfunctions reveal significant galaxy-to-galaxy variations in stellar content.Star-forming activity in the central arcmin of NGC300 has been suppressed forthe past Gyr with respect to disk fields at larger radii. Nevertheless,comparisons between fields within each galaxy indicate that star-formingactivity during intermediate epochs was coherent on spatial scales of a kpc ormore. A large cluster of stars, which isochrones suggest has an age near 100Myr, is seen in one of the NGC55 fields. The luminosity function of thebrightest stars in this cluster is flat, as expected if a linearluminosity-core mass relation is present.Comment: 30 pages, including 13 figure