The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III (1101.1559v2)

Abstract: The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with new instrumentation and new surveys focused on Galactic structure and chemical evolution, measurements of the baryon oscillation feature in the clustering of galaxies and the quasar Ly alpha forest, and a radial velocity search for planets around ~8000 stars. This paper describes the first data release of SDSS-III (and the eighth counting from the beginning of the SDSS). The release includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap, bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a third of the Celestial Sphere. All the imaging data have been reprocessed with an improved sky-subtraction algorithm and a final, self-consistent photometric recalibration and flat-field determination. This release also includes all data from the second phase of the Sloan Extension for Galactic Understanding and Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars at both high and low Galactic latitudes. All the more than half a million stellar spectra obtained with the SDSS spectrograph have been reprocessed through an improved stellar parameters pipeline, which has better determination of metallicity for high metallicity stars.

• The paper introduces SDSS DR8's inaugural dataset from SDSS-III, showcasing advances in imaging and spectroscopy techniques.
• It details reprocessing of imaging data over 14,555 deg² with improved sky subtraction and photometric calibration.
• The study employs the updated idlspec2d pipeline for spectroscopic analysis, enhancing redshift and stellar parameter measurements.

An Overview of the Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III

The eighth data release (DR8) from the Sloan Digital Sky Survey (SDSS) marks the inaugural data availability from the SDSS-III suite of surveys. As an extension of the successful SDSS project, this release not only continues the legacy of providing comprehensive astronomical datasets but also includes new advancements in data collection and processing techniques. This release is distinguished by its comprehensive reprocessing of imaging data, encompassing updates in photometric calibration, sky subtraction algorithms, and spectroscopic data analysis.

Imaging Data and Coverage

DR8 includes imaging data across approximately 14,555 deg$^2$ of the sky, contributing to a total imaging footprint of over one-third of the celestial sphere. Notably, this release includes new data from the Southern Galactic Cap, adding about 2500 deg$^2$ of coverage. This imaging expansion was vital for spectroscopic targeting in subsequent surveys, such as the Baryon Oscillation Spectroscopic Survey (BOSS). The reprocessing of imaging data employs improved sky subtraction techniques, aiming to reduce the previous systematic underestimation of the brightness in large galaxies.

The imaging pipeline improvements are expected to ameliorate issues related to the suppression of faint galaxy counts near bright galaxies, an area critical for lensing and clustering studies. These enhancements, however, are not yet deemed to fully address all systematic errors in photometric measurements, particularly for very large galaxies.

Spectroscopy and Integrative Surveys

DR8 presents a significant update in spectroscopic data, incorporating over 1.6 million spectra from galaxies, quasars, and stars. This includes approximately 118,000 stellar spectra from the SEGUE-2 survey, which focus on understanding the distant halo of the Milky Way. Despite the intended depth of SEGUE-2, aimed at distant halo components, improvements in target selection criteria for various stellar populations have been included to maximize survey efficiency and data utility.

The spectroscopic classification and redshift measurement process now relies on the $\texttt{idlspec2d}$ pipeline, which supersedes $\texttt{spectro1d}$, enhancing the consistency and reliability across datasets. Additionally, the analysis benefits from the deployment of enhanced techniques for emission-line measurement and stellar parameter estimation, particularly advantageous for metal-rich star classifications.

Enhancements and Theoretical Implications

The release embodies substantive updates in photometric and spectroscopic methodologies, which translate into more precise and reliable datasets. These advancements have implications not only for optical survey strategies but also for the calibration of theoretical models concerning Galactic structure and evolution. Specifically, the nebular emission-line and stellar continuum modeling improvements aid in refining chemical abundance measurements and star-formation histories.

The participation of SDSS-III in the broader scientific community's endeavors toward understanding cosmic phenomena is underpinned by the thorough integration and calibration of these datasets. The consistency and depth afforded by DR8 set a robust foundation for the subsequent surveys under the SDSS-III banner, influencing future research in astrophysical dynamics and cosmology.

Future Considerations

Moving forward, the SDSS-III continues with various integrative surveys, including BOSS and the APO Galactic Evolution Experiment (APOGEE), each promising to yield significant insights into cosmic expansion and galactic evolution. The enhancements made in DR8 pave the way for these future endeavors, contributing to a cumulative and refined framework that supports a multitude of astronomical studies. Subsequent data releases will undoubtedly build upon this foundation, ensuring the continued provision of transformative data to the scientific community.