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Title: PANCHROMATIC HUBBLE ANDROMEDA TREASURY. XII. MAPPING STELLAR METALLICITY DISTRIBUTIONS IN M31

We present a study of spatial variations in the metallicity of old red giant branch stars in the Andromeda galaxy. Photometric metallicity estimates are derived by interpolating isochrones for over seven million stars in the Panchromatic Hubble Andromeda Treasury (PHAT) survey. This is the first systematic study of stellar metallicities over the inner 20 kpc of Andromeda’s galactic disk. We see a clear metallicity gradient of −0.020 ± 0.004 dex kpc{sup −1} from ∼4–20 kpc assuming a constant red giant branch age. This metallicity gradient is derived after correcting for the effects of photometric bias and completeness and dust extinction, and is quite insensitive to these effects. The unknown age gradient in M31's disk creates the dominant systematic uncertainty in our derived metallicity gradient. However, spectroscopic analyses of galaxies similar to M31 show that they typically have small age gradients that make this systematic error comparable to the 1σ error on our metallicity gradient measurement. In addition to the metallicity gradient, we observe an asymmetric local enhancement in metallicity at radii of 3–6 kpc that appears to be associated with Andromeda’s elongated bar. This same region also appears to have an enhanced stellar density and velocity dispersion.
Authors:
;  [1] ; ; ; ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ; ;  [9] ;  [10] ;  [11] ;  [12]
  1. Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States)
  2. Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States)
  3. McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213 (United States)
  4. Osservatorio Astronomico di Padova—INAF, Vicolo dell’Osservatori 5, I-35122 Padova (Italy)
  5. Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455 (United States)
  6. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
  7. Raytheon, 1151 E. Hermans Road, Tucson, AZ 85706 (United States)
  8. MPIA, Koenigstuhl 17, D-69117 Heidelberg (Germany)
  9. UCO/Lick Observatory, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States)
  10. Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)
  11. MPA, Garching (Germany)
  12. NOAO, Tucson, AZ 85719 (United States)
Publication Date:
OSTI Identifier:
22520060
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 150; Journal Issue: 6; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASYMMETRY; COMPARATIVE EVALUATIONS; DENSITY; GALAXIES; METALLICITY; PHOTOMETRY; RED GIANT STARS; STAR EVOLUTION; VARIATIONS