PANCHROMATIC HUBBLE ANDROMEDA TREASURY. XII. MAPPING STELLAR METALLICITY DISTRIBUTIONS in M31

Dylan Gregersen; Anil C. Seth; Benjamin F. Williams; Dustin Lang; Julianne J. Dalcanton; Leó Girardi; Evan D. Skillman; Eric Bell; Andrew E. Dolphin; Morgan Fouesneau; Puragra Guhathakurta; Katherine M. Hamren; L. C. Johnson; Jason Kalirai; Alexia R. Lewis; Antonela Monachesi; Knut Olsen

doi:10.1088/0004-6256/150/6/189

PANCHROMATIC HUBBLE ANDROMEDA TREASURY. XII. MAPPING STELLAR METALLICITY DISTRIBUTIONS in M31

Dylan Gregersen, Anil C. Seth, Benjamin F. Williams, Dustin Lang, Julianne J. Dalcanton, Leó Girardi, Evan D. Skillman, Eric Bell, Andrew E. Dolphin, Morgan Fouesneau, Puragra Guhathakurta, Katherine M. Hamren, L. C. Johnson, Jason Kalirai, Alexia R. Lewis, Antonela Monachesi, Knut Olsen

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Abstract

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.

Original language	English (US)
Article number	189
Journal	Astronomical Journal
Volume	150
Issue number	6
DOIs	https://doi.org/10.1088/0004-6256/150/6/189
State	Published - Dec 1 2015

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© 2015. The American Astronomical Society. All rights reserved.

Keywords

galaxies: evolution
galaxies: individual (M31) galaxies: photometry
galaxies: stellar content
galaxies: structure
stars: abundances

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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., R. Lewis, A., Monachesi, A., & Olsen, K. (2015). PANCHROMATIC HUBBLE ANDROMEDA TREASURY. XII. MAPPING STELLAR METALLICITY DISTRIBUTIONS in M31. Astronomical Journal, 150(6), Article 189. https://doi.org/10.1088/0004-6256/150/6/189

Gregersen, D, Seth, AC, Williams, BF, Lang, D, Dalcanton, JJ, Girardi, L, Skillman, ED, Bell, E, Dolphin, AE, Fouesneau, M, Guhathakurta, P, Hamren, KM, Johnson, LC, Kalirai, J, R. Lewis, A, Monachesi, A & Olsen, K 2015, 'PANCHROMATIC HUBBLE ANDROMEDA TREASURY. XII. MAPPING STELLAR METALLICITY DISTRIBUTIONS in M31', Astronomical Journal, vol. 150, no. 6, 189. https://doi.org/10.1088/0004-6256/150/6/189

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abstract = "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.",

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AU - Seth, Anil C.

AU - Williams, Benjamin F.

AU - Lang, Dustin

AU - Dalcanton, Julianne J.

AU - Girardi, Leó

AU - Skillman, Evan D.

AU - Bell, Eric

AU - Dolphin, Andrew E.

AU - Fouesneau, Morgan

AU - Guhathakurta, Puragra

AU - Hamren, Katherine M.

AU - Johnson, L. C.

AU - Kalirai, Jason

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AU - Monachesi, Antonela

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AB - 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.

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KW - galaxies: individual (M31) galaxies: photometry

KW - galaxies: stellar content

KW - galaxies: structure

KW - stars: abundances

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PANCHROMATIC HUBBLE ANDROMEDA TREASURY. XII. MAPPING STELLAR METALLICITY DISTRIBUTIONS in M31

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Keywords

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