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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 730229.0, MPI für Astronomie / Publikationen_mpia
Panchromatic Hubble Andromeda Treasury. XII. Mapping stellar metallicity distributions in M31
Authors:Gregersen, D.; Seth, A. C.; Williams, B. F.; Lang, D.; Dalcanton, J. J.; Girardi, L.; Skillman, E. D.; Bell, E.; Dolphin, A. E.; Fouesneau, M.; Guhathakurta, P.; Hamren, K. M.; Johnson, L. C.; Kalirai, J.; Lewis, A. R.; Monachesi, A.; Olsen, K.
Date of Publication (YYYY-MM-DD):2015
Title of Journal:The Astronomical Journal
Issue / Number:6
Start Page:id. 189 (12 pp)
Audience:Not Specified
Abstract / Description: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‑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.
Free Keywords:galaxies: evolution; galaxies: individual: M31; galaxies: photometry; galaxies: stellar content; galaxies: structure; stars: abundances
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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