SDSS-IV eBOSS emission-line galaxy pilot survey

TL;DR

This paper evaluates different emission-line galaxy selection algorithms for the SDSS-IV/eBOSS survey, ensuring reliable redshift measurements for BAO studies at redshift 0.9, and identifies the most effective selection method for future application.

Contribution

It provides a detailed comparison of target selection algorithms for ELGs, validating their redshift quality and recommending the best algorithm for eBOSS based on survey efficiency.

Findings

Automated pipeline redshifts meet quality standards for BAO analysis.

Correlation between sky emission, S/N ratio, and redshift error identified.

Best target selection algorithm recommended for DECam photometry.

Abstract

The Sloan Digital Sky Survey IV extended Baryonic Oscillation Spectroscopic Survey (SDSS-IV/eBOSS) will observe 195,000 emission-line galaxies (ELGs) to measure the Baryonic Acoustic Oscillation standard ruler (BAO) at redshift 0.9. To test different ELG selection algorithms, 9,000 spectra were observed with the SDSS spectrograph as a pilot survey based on data from several imaging surveys. First, using visual inspection and redshift quality flags, we show that the automated spectroscopic redshifts assigned by the pipeline meet the quality requirements for a reliable BAO measurement. We also show the correlations between sky emission, signal-to-noise ratio in the emission lines, and redshift error. Then we provide a detailed description of each target selection algorithm we tested and compare them with the requirements of the eBOSS experiment. As a result, we provide reliable redshift distributions for the different target selection schemes we tested. Finally, we determine an target selection algorithms that is best suited to be applied on DECam photometry because they fulfill the eBOSS survey efficiency requirements.