SDSS-III banner: still mapping the universe

SEGUE-2 and APOGEE: Mapping the Milky Way

SDSS-III features two complementary surveys aimed at understanding the Milky Way: SEGUE-2 will map the outer parts of the Galaxy, and APOGEE will use infrared spectroscopy to penetrate the dust obscuring the inner Galaxy.

SEGUE-2 at a glance
Dark time observations, Fall 2008 - Spring 2009 250,000 stars in multiple categories, to magnitude g=19 Resolution R~2000, typical S/N=25 wavelengths 385-920 nm Velocity error 4 km/s, [Fe/H] error 0.3 dex Bright time parallel program, 2010-2014: additional 100,000 stars to g=17

SEGUE-2 will map the outer Milky Way with spectra of 250,000 stars, doubling the sample of the SEGUE (Sloan Extension for Galactic Understanding and Exploration) component of SDSS-II. These measurements reveal the complex kinematic and chemical substructure of the Galactic halo and disks, providing essential clues to the assembly and enrichment history of the Galaxy. They uncover rare, chemically primitive stars that are fossils of the earliest generations of cosmic star formation.

Colored map of stars in the northern sky, with star streams labeled and dwarf galaxies as insets

SDSS stellar map of the northern sky, showing trails and streams of stars torn from disrupted Milky Way satellites. Insets show new dwarf companions discovered by the SDSS (credit: V. Belokurov).

APOGEE at a glance
Bright time observations, Spring 2011 - Spring 2014 300-fiber cryogenic spectrograph, resolution R~20,000, S/N=100 wavelengths 1.52-1.69 μm Velocity error 0.5 km/s Abundances of more than 15 elements 100,000 2MASS-selected giant stars to H=13.5, probing all Galactic populations

The APO Galactic Evolution Experiment (APOGEE) will use high-resolution, high signal-to-noise infrared spectroscopy to penetrate the dust that obscures the inner Galaxy. APOGEE will survey 100,000 red giant stars across the full range of the Galactic bulge, bar, disk, and halo. Precise radial velocities and detailed chemical abundance "fingerprinting" will provide unprecedented insights into the dynamical structure and chemical history of the Galaxy.

The SEGUE-II and APOGEE datasets will play a central role in near-field cosmology tests of galaxy formation and the small-scale distribution of dark matter.

For detailed descriptions of SEGUE-2 and APOGEE, see sections 4 and 5 of the Project Description, available as a PDF document.

Map of the Milky Way, from 2MASS. The galactic disk and bulge appear bright.

2MASS map of the Milky Way, including light of half a billion stars. Only infrared observations penetrated to the dust-obscured inner galaxy (credit: 2MASS, J. Carpenter, T. Jarret, R. Hurt).