DOE OSTI2016
“Cosmological redshift surveys” are experiments conducted with astronomical telescopes, imagers, and spectrographs, which map the three-dimensional structure of the universe on the largest scales. These maps are delineated by the positions of galaxies, quasars, and intergalactic hydrogen clouds. When interpreted in the context of Einstein’s theory of gravity, these maps can be used to infer the nature of the contents of the universe, including the mysterious “dark energy” that is driving the expansion of the universe to accelerate. While the directional positions of galaxies and other objects can be measured directly in images of the sky, the third dimension of their position (i.e., their distance from the Earth and the Milky Way Galaxy) must be measured by spectrographs that distribute their light as a function of frequency, enabling a measurement of their cosmological Doppler shift (or “redshift”), which serves as an observable proxy for distance. The largest cosmological redshift surveys, such as the “eBOSS” experiment of the fourth Sloan Digital Sky Survey, collect spectroscopic data for hundreds of thousands to millions of galaxies. Future experiments such as the Dark Energy Spectroscopic Instrument will in turn collect tens of millions of spectra. To be feasible, redshift measurement methods in datasets of this scale must be made with automated software. This paper describes the algorithms, astrophysical templates, and implementation of a new redshift measurement software package that is optimized to run on large numbers of spectra with relatively low signal-to-noise ratio, typical of the most ambitious current and future cosmological redshift surveys. The software is demonstrated on spectroscopic data from the eBOSS survey, with performance that meets the scientific requirements of that experiment. The software is implemented in a general framework that will allow application to spectra from the DESI project in the future.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗