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H. C. Ferguson (STScI), R. M. Rich (UCLA), T. M. Brown, T. E. Smith (STScI), M. Mouhcine (UCLA)
Were the extended stellar halos the first stellar populations to form in spiral galaxies, or have they been accreted over time from dwarf galaxies? What are the systematic relations between the disk, the bulge and the halo? Does stellar mass of the halo scale with the mass of the bulge or the mass of the entire galaxy? To begin to address such questions we observed nine nearby spiral galaxies with WFPC2 and resolved the top few magnitudes of the red-giant branch in the halo population. Specifically, the WFPC2 fields were placed 2 to 13 kpc off the minor-axis of the disks of NGC55, 247, 253, 300, 2903, 3031, 4244, 4258, and 4945. These observations allow the first systematic study of the spatial distributions, metallicities and metallicity distributions of halo stars in normal spiral galaxies outside of the Local Group. We present a preliminary analysis of the color-magnitude diagrams including: estimates of the mean metallicities and metallicity distributions of each galaxy, estimates of the TRGB distances, estimates of the radial density profiles and a search for metallicity gradients, and first look at systematic trends within the sample of galaxies.
This work is supported by a grant from STScI which is operated by AURA for NASA.