The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey

Abstract: The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar spectra, along with the data presented in previous data releases. These spectra were obtained with the new BOSS spectrograph and were taken between 2009 December and 2011 July. In addition, the stellar parameters pipeline, which determines radial velocities, surface temperatures, surface gravities, and metallicities of stars, has been updated and refined with improvements in temperature estimates for stars with T_eff<5000 K and in metallicity estimates for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars presented in DR8, including stars from SDSS-I and II, as well as those observed as part of the SDSS-III Sloan Extension for Galactic Understanding and Exploration-2 (SEGUE-2). The astrometry error introduced in the DR8 imaging catalogs has been corrected in the DR9 data products. The next data release for SDSS-III will be in Summer 2013, which will present the first data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) along with another year of data from BOSS, followed by the final SDSS-III data release in December 2014.

• The paper introduces the first BOSS spectroscopic data release, significantly expanding SDSS-III’s archive with detailed observations of galaxies, quasars, and stars.
• It employs advanced instrumentation upgrades—including increased fiber counts and improved spectral resolution—to boost data quality and coverage.
• The dataset enables precise studies of the universe’s large-scale structure and dark energy dynamics through baryon acoustic oscillation analysis.

Overview of the Ninth Data Release of the Sloan Digital Sky Survey

The Ninth Data Release (DR9) of the Sloan Digital Sky Survey (SDSS) marks a significant advancement in the ongoing SDSS-III initiative, particularly through incorporating the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This release represents a substantial dataset within the SDSS project's larger framework, reflecting sophisticated instrumentation and refined methodologies to enhance astronomical data acquisition.

Methodology and Data Scope

The DR9 dataset is a culmination of 1.5 years of meticulous observations utilizing the BOSS spectrograph and extends SDSS-III's reach in probing the cosmos. It comprises 535,995 galaxy, 102,100 quasar, and 90,897 stellar spectra. The galaxies' spectra predominantly range from median redshifts of about $z \sim 0.52$, while the quasar spectra engage deeper into the universe at median redshifts around $z \sim 2.32$. Such extensive coverage facilitates probing the universe's large-scale structure and the baryon oscillation phenomenon as a cosmic standard ruler, offering insights into dark energy dynamics.

Instrumentation Advances

The transformation from SDSS-I/II to BOSS involved major upgrades to both the physical and operational capabilities of the spectrograph. Notable changes include an increase in fiber count from 640 to 1000, new volume phase holographic gratings for higher throughput, and a broader spectral coverage from 360 to 1040 nm, surpassing the previous 380 to 920 nm range. These advancements have enhanced spectral resolution significantly and improved overall observation efficiency.

Data Release Components

DR9 not only rectifies prior astrometric errors identified in DR8 but also augments the scope by recalibrating the astrometric solution, ensuring precision in high-declination object positioning. The dataset also updates the stellar parameter pipeline with novel temperature and metallicity estimation improvements, crucial for more accurately characterizing celestial objects.

Theoretical and Practical Implications

The data from DR9, combined with sophisticated algorithmic processing, provide a platform for both theoretical advancements in understanding the universe's large-scale structure and practical astronomical investigations. The precise measurement of the baryon acoustic oscillation scale across different epochs aids in constraining cosmological models, particularly those addressing dark energy's role in the universe's expansion.

Moreover, the comprehensive quasar dataset, tailored to enhance signal-to-noise ratios especially for Lyman-alpha forest analyses, positions researchers to explore the intergalactic medium's properties at high redshifts. DR9's contribution to mapping the critical phases in the universe's expansion history cannot be overstated, offering substantial data to challenge and refine current cosmological theories.

Future Prospects

Looking forward, subsequent data releases are anticipated to encompass additional datasets from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and ongoing BOSS operations, broadening the horizon for multi-faceted astronomical exploration within the SDSS-III framework. Each release promises further enhancement of the overall catalog, enriching our understanding of galactic structure and evolution.

In conclusion, DR9 embodies a pivotal progression in the SDSS-III initiative, standing as a testament to the ambition and technical mastery that define modern astronomical surveys. It lays the groundwork for future breakthroughs in our understanding of cosmic phenomena, fostering a deeper comprehension of universe dynamics and the fundamental aspects governing them.