F Turnoff Distribution in the Galactic Halo Using Globular Clusters as Proxies

Abstract

F turnoff stars are important tools for studying Galactic halo substructure because they are plentiful, luminous, and can be easily selected by their photometric colors from large surveys such as the Sloan Digital Sky Survey (SDSS). We describe the absolute magnitude distribution of color-selected F turnoff stars, as measured from SDSS data, for eleven globular clusters in the Milky Way halo. We find that the M_g distribution of turnoff stars is intrinsically the same for all clusters studied, and is well fit by two half Gaussian functions, centered at mu=4.18, with a bright-side sigma=0.36, and with a faint-side sigma=0.76. However, the color errors and detection efficiencies cause the observed sigma of the faint-side Gaussian to change with magnitude due to contamination from redder main sequence stars (40% at 21st magnitude). We present a function that will correct for this magnitude-dependent change in selected stellar populations, when calculating stellar density from color-selected turnoff stars. We also present a consistent set of distances, ages and metallicities for eleven clusters in the SDSS Data Release 7. We calculate a linear correction function to Padova isochrones so that they are consistent with SDSS globular cluster data from previous papers. We show that our cluster population falls along the Milky Way Age-Metallicity Relationship (AMR), and further find that isochrones for stellar populations on the AMR have very similar turnoffs; increasing metallicity and decreasing age conspire to produce similar turnoff magnitudes and colors for all old clusters that lie on the AMR.

Accepted for publication in ApJ, 32 pages, 18 figures

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Cited by in corpus (13)

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• The Metallicity Distribution Functions of SEGUE G and K dwarfs: Constraints for Disk Chemical Evolution and Formation
• The Complex Structure of Stars in the Outer Galactic Disk as revealed by Pan-STARRS1
• Mapping the Monoceros Ring in 3D with Pan-STARRS1
• On Rings and Streams in the Galactic Anti-Center
• Stellar Velocity Dispersion and Anisotropy of the Milky Way Inner Halo
• A Spatial Characterization of the Sagittarius Dwarf Galaxy Tidal Tails
• A tangle of stellar streams in the north Galactic cap
• Fitting the density substructure of the stellar halo with MilkyWay@home
• Introduction to Tidal Streams
• MilkyWay@home: Harnessing volunteer computers to constrain dark matter in the Milky Way
• Determining distances to stars statistically from photometry