Final Scientific/Technical Report

Abstract

The ultimate goal of this project was to better understand the nature of dark energy. Dark energy is a mysterious component of the Universe that is causing the acceleration of the cosmic expansion rate. The best measurements of this rate are consistent with dark energy in the form of a cosmological constant. This means that the component responsible for the expansion has not changed in strength in the history of the universe, although it did not appear make a significant impact on the expansion rate for the first half of cosmic history. As almost nothing is known about dark energy other than that the expansion rate is presently accelerating, there are many substantial efforts underway to obtain better data to determine if dark energy is truly consistent with a cosmological constant, or if there is any evidence of evolution. The Dark Energy Spectroscopic Instrument (DESI) is a new survey planned to begin in 2019 that will obtain substantially better measurements of the cosmic expansion rate than previous surveys. The main technique it will use is Baryon Acoustic Oscillations (BAO). The BAO scale corresponds to a fixed physical length scale or ‘standard ruler’ that was imprinted on the distribution of baryons in the early universe. DESI will measure this scale over most of the age of the universe, and will consequently provide the best measurement of the dark energy contribution. At the earliest times, DESI will use measurements of rare but luminous quasars for the BAO measurements through observations of neutral Hydrogen absorption along the line of sight to each quasar. While supported by these funds, I contributed to the construction of the DESI spectrographs that will record these measurements. I also became deeply involved in other aspects of the DESI experiment, and was chosen to become the Instrument Scientist for the entire DESI Project. During the project period I also worked on quasar selection techniques with data from the Dark Energy Survey (DES), which may be adopted by DESI.