1998/03/23 by T. J. Davidge · 2 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/305495
30 pages, including 13 figures
arxiv created 1998/03/23 · openalex publication_date 1998/04/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
Deep J , H , and K images are used to probe the evolved stellar contents in the central regions of the Sculptor Group galaxies NGC 55, NGC 300, and NGC 7793. The brightest stars are massive red supergiants (RSGs) with K ~ 15-15.5. The peak RSG brightness is constant to within ~0.5 mag in K , suggesting that NGC 55, NGC 300, and NGC 7793 are at comparable distances. Comparisons with bright RSGs in the Magellanic Clouds indicate that the difference in distance modulus with respect to the LMC is Δμ = 7.5 mag. A rich population of asymptotic giant branch (AGB) stars, which isochrones indicate have ages between 0.1 and 10 Gyr, is also seen in the ( K , J - K ) color-magnitude diagram (CMD) of each galaxy. The detection of significant numbers of AGB stars with ages near 10 Gyr indicates that the disks of these galaxies contain an underlying old population. The CMDs and luminosity functions reveal significant galaxy-to-galaxy variations in stellar content. Star-forming activity in the central arcminute of NGC 300 has been suppressed for the past 10 9 yr with respect to disk fields at larger radii. Nevertheless, comparisons between fields within each galaxy indicate that star-forming activity during intermediate epochs was coherent on spatial scales of a kiloparsec or more. A large cluster of stars, which isochrones suggest has an age near 100 Myr, is seen in one of the NGC 55 fields. The luminosity function of the brightest stars in this cluster is flat, as expected if a linear luminosity-core mass relation is present.