Predicting Quasar Continua near Lyα with Principal Component Analysis

Frederick B. Davies, Joseph F. Hennawi, Eduardo Bañados, Robert A. Simcoe, Roberto Decarli, Xiaohui Fan, Emanuele P. Farina, Chiara Mazzucchelli, Hans Walter Rix, Bram P. Venemans, Fabian Walter, Feige Wang, Jinyi Yang

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

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 λ rest ∼ 1200-1260 Å. 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 ∼ 2-2.5 quasars from the Sloan Digital Sky Survey (SDSS)/Baryon Oscillation Spectroscopic Survey (BOSS) into 10 red-side (1280 Å < λ rest < 2900 Å) and 6 blue-side (1180 Å < λ rest < 1280 Å) PCA basis spectra, and constructed a projection matrix to predict the blue-side coefficients from a fit to the red-side spectrum. We found that our method predicts the blue-side continuum with ∼6%-12% precision and ≲1% bias by testing on the full training set sample. We then computed predictions for the blue-side continua of the two quasars currently known at z >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 Lyα.

Original languageEnglish (US)
Article number143
JournalAstrophysical Journal
Volume864
Issue number2
DOIs
StatePublished - Sep 10 2018

Fingerprint

principal components analysis
quasars
principal component analysis
continuums
wavelength
wings
damping
education
wavelengths
prediction
predictions
artifact
artifacts
baryons
near infrared
oscillation
time measurement
hydrogen
calibration
oscillations

Keywords

  • cosmology: observations
  • methods: numerical
  • quasars: emission lines
  • quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Davies, F. B., Hennawi, J. F., Bañados, E., Simcoe, R. A., Decarli, R., Fan, X., ... Yang, J. (2018). Predicting Quasar Continua near Lyα with Principal Component Analysis. Astrophysical Journal, 864(2), [143]. https://doi.org/10.3847/1538-4357/aad7f8

Predicting Quasar Continua near Lyα with Principal Component Analysis. / Davies, Frederick B.; Hennawi, Joseph F.; Bañados, Eduardo; Simcoe, Robert A.; Decarli, Roberto; Fan, Xiaohui; Farina, Emanuele P.; Mazzucchelli, Chiara; Rix, Hans Walter; Venemans, Bram P.; Walter, Fabian; Wang, Feige; Yang, Jinyi.

In: Astrophysical Journal, Vol. 864, No. 2, 143, 10.09.2018.

Research output: Contribution to journalArticle

Davies, FB, Hennawi, JF, Bañados, E, Simcoe, RA, Decarli, R, Fan, X, Farina, EP, Mazzucchelli, C, Rix, HW, Venemans, BP, Walter, F, Wang, F & Yang, J 2018, 'Predicting Quasar Continua near Lyα with Principal Component Analysis', Astrophysical Journal, vol. 864, no. 2, 143. https://doi.org/10.3847/1538-4357/aad7f8
Davies FB, Hennawi JF, Bañados E, Simcoe RA, Decarli R, Fan X et al. Predicting Quasar Continua near Lyα with Principal Component Analysis. Astrophysical Journal. 2018 Sep 10;864(2). 143. https://doi.org/10.3847/1538-4357/aad7f8
Davies, Frederick B. ; Hennawi, Joseph F. ; Bañados, Eduardo ; Simcoe, Robert A. ; Decarli, Roberto ; Fan, Xiaohui ; Farina, Emanuele P. ; Mazzucchelli, Chiara ; Rix, Hans Walter ; Venemans, Bram P. ; Walter, Fabian ; Wang, Feige ; Yang, Jinyi. / Predicting Quasar Continua near Lyα with Principal Component Analysis. In: Astrophysical Journal. 2018 ; Vol. 864, No. 2.
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abstract = "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 λ rest ∼ 1200-1260 {\AA}. 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 ∼ 2-2.5 quasars from the Sloan Digital Sky Survey (SDSS)/Baryon Oscillation Spectroscopic Survey (BOSS) into 10 red-side (1280 {\AA} < λ rest < 2900 {\AA}) and 6 blue-side (1180 {\AA} < λ rest < 1280 {\AA}) PCA basis spectra, and constructed a projection matrix to predict the blue-side coefficients from a fit to the red-side spectrum. We found that our method predicts the blue-side continuum with ∼6{\%}-12{\%} precision and ≲1{\%} bias by testing on the full training set sample. We then computed predictions for the blue-side continua of the two quasars currently known at z >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 Lyα.",
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