Predicting Quasar Continua near Ly alpha with Principal Component Analysis

Measuring the proximity effect and the damping wing of intergalactic neutral hydrogen in quasar spectra during the epoch of reionization requires an estimate of the intrinsic continuum at rest-frame wavelengths of lambda(rest) similar to 1200-1260 angstrom. In contrast to previous works which used composite spectra with matched spectral properties or explored correlations between parameters of broad emission lines, we opted for a nonparametric predictive approach based on principal component analysis (PCA) to predict the intrinsic spectrum from the spectral properties at redder (i. e., unabsorbed) wavelengths. We decomposed a sample of 12764 spectra of z similar to 2-2.5 quasars from the Sloan Digital Sky Survey (SDSS)/ Baryon Oscillation Spectroscopic Survey (BOSS) into 10 red-side (1280 angstrom 7: ULAS J1120+ 0641 (z = 7.09) and ULAS J1342+ 0928 (z = 7.54). Both of these quasars are known to exhibit extreme emission line properties, so we individually calibrated the uncertainty in the continuum predictions from similar quasars in the training set, finding comparable precision but moderately higher bias than the predictions for the training set as a whole, although they may face additional systematic uncertainties due to calibration artifacts present in near-infrared echelle spectra. We find that both z > 7 quasars, and in particular ULAS J1342+ 0928, show signs of damping wing-like absorption at wavelengths redward of Ly alpha.ERC grant "Cosmic Dawn"; Alfred P. Sloan Foundation; National Science Foundation; U.S. Department of Energy Office of Science; University of Arizona; Brazilian Participation Group; Brookhaven National Laboratory; Carnegie Mellon University; University of Florida; French Participation Group; German Participation Group; Harvard University; Instituto de Astrofisica de Canarias; Michigan State/Notre Dame/JINA Participation Group; Johns Hopkins University; Lawrence Berkeley National Laboratory; Max Planck Institute for Astrophysics; Max Planck Institute for Extraterrestrial Physics; New Mexico State University; New York University; Ohio State University; Pennsylvania State University; University of Portsmouth; Princeton University; Spanish Participation Group; University of Tokyo; University of Utah; Vanderbilt University; University of Virginia; University of Washington; Yale University; [ULAS J1342+0928]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu