The Metallicity Distribution Functions of SEGUE G and K dwarfs: Constraints for Disk Chemical Evolution and Formation

Details The Metallicity Distribution Functions of SEGUE G and K dwarfs: Constraints for Disk Chemical Evolution and Formation The Metallicity Distribution Functions of SEGUE G and K dwarfs: Constraints for Disk Chemical Evolution and Formation

2011-12-09

arxiv.org/abs/1112.2214v1

Astronomy and Astrophysics

Astrophysics

Solar and Stellar Astrophysics

74 pages, 25 figures, 9 tables. Submitted to The Astrophysical Journal

Scientific paper

Using the G and K dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey, we determine the metallicity distributions of cool stars in the Milky Way disk system. This portion of the Sloan Digital Sky Survey (SDSS) contains spectra for approximately 41,500 G and 23,800 K dwarfs, a larger sample, numerically and spatially, than previous spectroscopic analyses. SEGUE has a quantitative target-selection algorithm which we use to ensure that our sample accurately represents the underlying Milky Way populations. Using estimated distances, with uncertainties of 12%, we quantify the variation in metallicity with respect to spatial position from the Galactic center (R) and the plane of the Galaxy (|Z|). We are consistent with the results from Cheng et al., estimating a negative gradient below |Z| of 1 kpc that flattens above this height. Both spectral types also exhibit a consistent decrease in [Fe/H] with increasing |Z|, approximately -0.3 dex/kpc, which reflects the transition from a thin-disk-dominated sample at small |Z| to a sample consisting primarily of thick-disk stars at heights above |Z| of 1 kpc. We compare our distributions to those of two different models of the Galaxy, neither of which is able to replicate the metallicity distributions we observe above |Z| of 0.5 kpc, likely because they are calibrated on thin-disk-dominated, local samples. Our unbiased observations of G and K dwarfs provide valuable constraints for chemical and dynamical Galaxy evolution models, with particular utility for thin- and thick-disk formation theory. (edited)

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