The Milky Way Tomography with SDSS. 2. Stellar Metallicity Metadata

Title

• Main Title The Milky Way Tomography with SDSS. 2. Stellar Metallicity

Creator

• Author: Ivezic, Zeljko
  Creator Type: Personal
• Author: Sesar, Branimir
  Creator Type: Personal
• Author: Juric, Mario
  Creator Type: Personal
• Author: Bond, Nicholas
  Creator Type: Personal
• Author: Dalcanton, Julianne
  Creator Type: Personal
• Author: Rockosi, Constance M.
  Creator Type: Personal
• Author: Yanny, Brian
  Creator Type: Personal
• Author: Newberg, Heidi J.
  Creator Type: Personal
• Author: Beers, Timothy C.
  Creator Type: Personal
• Author: Prieto, Carlos Allende
  Creator Type: Personal
• Author: Wilhelm, Ron
  Creator Type: Personal

Contributor

• Sponsor: United States. Department of Energy.
  Contributor Type: Organization

Publisher

• Name: Fermi National Accelerator Laboratory
  Place of Publication: Batavia, Illinois
  Additional Info: Fermi National Accelerator Laboratory (FNAL), Batavia, IL

Date

• Creation: 2008-04-01

Language

• English

Description

• Content Description: In addition to optical photometry of unprecedented quality, the Sloan Digital Sky Survey (SDSS) is producing a massive spectroscopic database which already contains over 280,000 stellar spectra. Using effective temperature and metallicity derived from SDSS spectra for {approx}60,000 F and G type main sequence stars (0.2 < g-r < 0.6), we develop polynomial models, reminiscent of traditional methods based on the UBV photometry, for estimating these parameters from the SDSS u-g and g-r colors. These estimators reproduce SDSS spectroscopic parameters with a root-mean-square scatter of 100 K for effective temperature, and 0.2 dex for metallicity (limited by photometric errors), which are similar to random and systematic uncertainties in spectroscopic determinations. We apply this method to a photometric catalog of coadded SDSS observations and study the photometric metallicity distribution of {approx}200,000 F and G type stars observed in 300 deg{sup 2} of high Galactic latitude sky. These deeper (g < 20.5) and photometrically precise ({approx}0.01 mag) coadded data enable an accurate measurement of the unbiased metallicity distribution for a complete volume-limited sample of stars at distances between 500 pc and 8 kpc. The metallicity distribution can be exquisitely modeled using two components with a spatially varying number ratio, that correspond to disk and halo. The best-fit number ratio of the two components is consistent with that implied by the decomposition of stellar counts profiles into exponential disk and power-law halo components by Juric et al. (2008). The two components also possess the kinematics expected for disk and halo stars. The metallicity of the halo component can be modeled as a spatially invariant Gaussian distribution with a mean of [Fe/H] = -1.46 and a standard deviation of {approx}0.3 dex. The disk metallicity distribution is non-Gaussian, with a remarkably small scatter (rms {approx}0.16 dex) and the median smoothly decreasing with distance from the plane from -0.6 at 500 pc to -0.8 beyond several kpc. Similarly, we find using proper motion measurements that a non-Gaussian rotational velocity distribution of disk stars shifts by {approx}50 km/s as the distance from the plane increases from 500 pc to several kpc. Despite this similarity, the metallicity and rotational velocity distributions of disk stars are not correlated (Kendall's {tau} = 0.017 {+-} 0.018). This absence of a correlation between metallicity and kinematics for disk stars is in a conflict with the traditional decomposition in terms of thin and thick disks, which predicts a strong correlation ({tau} = ?0.30 {+-} 0.04) at {approx}1 kpc from the mid-plane. Instead, the variation of the metallicity and rotational velocity distributions can be modeled using non-Gaussian functions that retain their shapes and only shift as the distance from the mid-plane increases. We also study the metallicity distribution using a shallower (g < 19.5) but much larger sample of close to three million stars in 8500 sq. deg. of sky included in SDSS Data Release 6. The large sky coverage enables the detection of coherent substructures in the kinematics-metallicity space, such as the Monoceros stream, which rotates faster than the LSR, and has a median metallicity of [Fe/H] = ?0.95, with an rms scatter of only {approx}0.15 dex. We extrapolate our results to the performance expected from the Large Synoptic Survey Telescope (LSST) and estimate that the LSST will obtain metallicity measurements accurate to 0.2 dex or better, with proper motion measurements accurate to {approx}0.2-0.5 mas/yr, for about 200 million F/G dwarf stars within a distance limit of {approx}100 kpc (g < 23.5).
• Physical Description: 40 pages

Subject

• Keyword: Spectra
• Keyword: Main Sequence Stars
• Keyword: Velocity Astrophysics
• Keyword: Milky Way
• Keyword: Sky
• Keyword: Detection
• Keyword: Stars
• STI Subject Categories: 71 Classical And Quantum Mechanics, General Physics
• Keyword: Polynomials
• Keyword: Astrophysics
• Keyword: Tomography
• Keyword: Photometry
• Keyword: Distribution
• Keyword: Telescopes
• Keyword: Proper Motion
• Keyword: Performance
• Keyword: Dwarf Stars

Collection

• Name: Office of Scientific & Technical Information Technical Reports
  Code: OSTI

Institution

• Name: UNT Libraries Government Documents Department
  Code: UNTGD

Resource Type

• Article

Format

• Text

Identifier

• Report No.: FERMILAB-PUB-08-164-CD
• Grant Number: AC02-07CH11359
• Office of Scientific & Technical Information Report Number: 934568
• Archival Resource Key: ark:/67531/metadc894900