Automated Measurement of Quasar Redshift with a Gaussian Process
  We develop an automated technique to measure quasar redshifts in the Baryon
Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS).
Our technique is an extension of an earlier Gaussian process method for
detecting damped Lyman-alpha absorbers (DLAs) in quasar spectra with known
redshifts. We apply this technique to a subsample of SDSS DR12 with BAL quasars
removed and redshift larger than 2.15. We show that we are broadly competitive
to existing quasar redshift estimators, disagreeing with the PCA redshift by
more than 0.5 in only 0.38% of spectra. Our method produces a probabilistic
density function for the quasar redshift, allowing quasar redshift uncertainty
to be propagated to downstream users. We apply this method to detecting DLAs,
accounting in a Bayesian fashion for redshift uncertainty. Compared to our
earlier method with a known quasar redshift, we have a moderate decrease in our
ability to detect DLAs, predominantly in the noisiest spectra. The area under
curve drops from 0.96 to 0.91. Our code is publicly available.
