SDSS-III Baryon Oscillation Spectroscopic Survey Data Release 12: galaxy target selection and large scale structure catalogues (1509.06529v2)

Abstract: The Baryon Oscillation Spectroscopic Survey (BOSS), part of the Sloan Digital Sky Survey (SDSS) III project, has provided the largest survey of galaxy redshifts available to date, in terms of both the number of galaxy redshifts measured by a single survey, and the effective cosmological volume covered. Key to analysing the clustering of these data to provide cosmological measurements is understanding the detailed properties of this sample. Potential issues include variations in the target catalogue caused by changes either in the targeting algorithm or properties of the data used, the pattern of spectroscopic observations, the spatial distribution of targets for which redshifts were not obtained, and variations in the target sky density due to observational systematics. We document here the target selection algorithms used to create the galaxy samples that comprise BOSS. We also present the algorithms used to create large scale structure catalogues for the final Data Release (DR12) samples and the associated random catalogues that quantify the survey mask. The algorithms are an evolution of those used by the BOSS team to construct catalogues from earlier data, and have been designed to accurately quantify the galaxy sample. The code used, designated MKSAMPLE, is released with this paper.

• The paper presents innovative galaxy target selection criteria for LOWZ and CMASS samples, significantly enhancing redshift completeness and survey precision.
• It details advanced methodologies such as upweighting for fibre collisions and systematic correction techniques, ensuring robust catalogue uniformity.
• The creation of comprehensive LSS catalogues covering 9,376 deg² enables precise measurements of cosmic distances through BAO and RSD analyses.

An Overview of SDSS-III Baryon Oscillation Spectroscopic Survey Data Release 12: Galaxy Target Selection and Catalogue Construction

The Sloan Digital Sky Survey (SDSS) has been pivotal in advancing our understanding of cosmology and the large-scale structure of the Universe. The Baryon Oscillation Spectroscopic Survey (BOSS), part of the SDSS-III initiative, represents the culmination of efforts to map the universe on an unprecedented scale by measuring the redshifts of over a million galaxies. This essay explores the methodologies and outcomes associated with the final data release, Data Release 12 (DR12), focusing primarily on the galaxy target selection processes and the construction of large-scale structure (LSS) catalogues.

Key Elements of Galaxy Targeting and Catalogue Compilation

1. Target Selection Criteria: The research outlines the target selection algorithms deployed to construct the BOSS galaxy samples. The LOWZ sample, which targets galaxies within redshift $z < 0.4$, extends the earlier SDSS luminous red galaxies (LRGs) to fainter magnitudes, thus increasing number density. The CMASS sample, designed for $0.4 < z < 0.7$, aims for a roughly constant stellar mass threshold across its redshift range, requiring sophisticated colour-magnitude cuts. Star-galaxy separation, a critical component of these selections, mitigates contamination from stars, particularly in the CMASS dataset.
2. Challenges and Solutions in Data Processing: Variability in the target catalogue owing to differences in observation conditions and the probabilistic nature of spectral measurements introduce significant challenges. The paper documents intricate algorithms to combat these variations, including the development of an upweighting method to correct for fibre collisions where two targets may be too close to both receive spectroscopic coverage.
3. Veto Masks and Systematic Corrections: The creation of veto masks and subsequent correction mechanisms for angular systematics (e.g., stellar density fluctuations, seeing conditions) are emphasized. The careful application of these techniques ensures the uniformity and reliability of the catalogue data, key for deriving precise cosmological parameters.
4. Implications for Future Cosmological Analyses: By generating the largest set of cosmological data from a single project to date, DR12 facilitates unprecedented opportunities for cosmological measurements, such as Baryon Acoustic Oscillations (BAO) and Redshift Space Distortions (RSD). Insights from the paper are expected to inform best practices for future surveys, like those planned for DESI and Euclid, addressing similar challenges at different scales.
5. Impactful Numerical Results: The DR12 catalogues cover 9,376 deg$^2$, providing a comprehensive survey footprint and achieving a nearly complete target completeness of 98% for CMASS and over 97% for LOWZ samples. These statistics are used to enhance the precision of cosmological distance measurements, impacting models of cosmic growth and pressure on alternative gravity theories.

Speculative Future Directions

As the landscape of cosmological surveys broadens, the methodologies honed through BOSS DR12 have laid groundwork essential for the next generation of spectroscopic surveys. Future advancements will likely involve increasing automation in data acquisition and reduction processes, improved algorithms for target selection in diverse sky conditions, and refined techniques for integrating multi-wavelength datasets to expand the scientific reach beyond the current redshift bounds.

In conclusion, the SDSS-III BOSS DR12 project not only concludes a significant phase in galaxy redshift surveys but also sets a rigorous standard for upcoming surveys. The careful design and implementation of targeting and catalogue compilation techniques described in this paper are instrumental for maximizing the accuracy of scientific inferences made from such large-scale survey data, forming a cornerstone for future exploration of the universe's large-scale structure.