The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Observational systematics and baryon acoustic oscillations in the correlation function

Abstract: We present baryon acoustic oscillation (BAO) scale measurements determined from the clustering of 1.2 million massive galaxies with redshifts 0.2 < z < 0.75 distributed over 9300 square degrees, as quantified by their redshift-space correlation function. In order to facilitate these measurements, we define, describe, and motivate the selection function for galaxies in the final data release (DR12) of the SDSS III Baryon Oscillation Spectroscopic Survey (BOSS). This includes the observational footprint, masks for image quality and Galactic extinction, and weights to account for density relationships intrinsic to the imaging and spectroscopic portions of the survey. We simulate the observed systematic trends in mock galaxy samples and demonstrate that they impart no bias on baryon acoustic oscillation (BAO) scale measurements and have a minor impact on the recovered statistical uncertainty. We measure transverse and radial BAO distance measurements in 0.2 < z < 0.5, 0.5 < z < 0.75, and (overlapping) 0.4 < z < 0.6 redshift bins. In each redshift bin, we obtain a precision that is 2.7 per cent or better on the radial distance and 1.6 per cent or better on the transverse distance. The combination of the redshift bins represents 1.8 per cent precision on the radial distance and 1.1 per cent precision on the transverse distance. This paper is part of a set that analyses the final galaxy clustering dataset from BOSS. The measurements and likelihoods presented here are combined with others in Alam et al. (2016) to produce the final cosmological constraints from BOSS.

• The paper presents precise BAO scale measurements, achieving 1.6% precision for transverse and 2.7% for radial distances.
• The paper employs mock catalogs to simulate observational biases and validate the selection function for unbiased clustering analysis.
• The paper confirms BAO as a reliable cosmological ruler, paving the way for more precise distance measurements in future surveys.

Overview of Baryon Acoustic Oscillations in BOSS Galaxy Clustering

The paper "The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Observational systematics and baryon acoustic oscillations in the correlation function" by Ross et al. focuses on the analysis of the correlation function of galaxies as part of the Baryon Oscillation Spectroscopic Survey (BOSS), a part of the Sloan Digital Sky Survey III (SDSS-III). The primary objective of this research is to examine the observational systematics involved in analyzing galaxy clustering and to make precise measurements of baryon acoustic oscillations (BAO) using the correlation function of these galaxies.

The analysis employs data from the SDSS-III BOSS, which provides a large sample of over 1.2 million galaxies with redshifts in the range $0.2 < z < 0.75$. The goal is to measure the BAO scale in the transverse and radial directions, which are key cosmological distance indicators. This is achieved by utilizing the redshift-space correlation function.

Key Methodologies

1. Selection Function and Observational Systematics:
   • The selection function is crucial in defining the BOSS galaxy samples, considering factors such as observational footprint, quality masks, and Galactic extinction. Any observational biases in density-weighted systems were simulated using mock galaxy samples to ensure that these systematics do not skew BAO scale measurements.
2. BAO Measurements:
   • The paper measures the transverse and radial BAO scales in different redshift bins. The precision achieved is at least 2.7% for radial distances and 1.6% for transverse distances across the redshift bins evaluated. The robustness of these measurements is validated versus the observational treatment of the selection function.
3. Mock Catalogs for Systematic Tests:
   • Different sets of mock catalogs simulate the observational systematics to validate the measurement techniques. The robustness of BAO scale measurements to these systematics was confirmed, indicating no significant bias from the systematics.

Results and Interpretation

The comprehensive simulations using mock catalogs and methodological checks suggest that the BAO measurements are not significantly influenced by observational systematics. The study finds that BAO scale measurements are a robust and reliable probe of cosmological distance scales. This resilience is attributed to the isolated nature of the BAO signal in configuration space, reducing susceptibility to systematic observational effects.

Implications

The findings have significant implications for cosmology, particularly for using BAO as a standard ruler to measure cosmic scales and expansion history accurately. The ability to measure these scales with high precision and minimal bias suggests the robustness of BAO as a tool in cosmological analysis. It also paves the way for enhancing methodologies for future galaxy surveys, where even more stringent demands on precision and control over systematics will be necessary.

Future Work

Continued work in improving the treatment of observational systematics will further solidify the reliability of BAO measurements from galaxy surveys. Moreover, combining results across different methodologies and surveys can refine distance scale measurements and enhance our understanding of the universe’s expansion history.

In summary, this study reinforces BAO as a solid method in cosmology by providing precise measurements that are validated against various observational systematics, setting a benchmark for future galaxy redshift surveys.