Probing Reionization with Quasar Spectra: the Impact of the Intrinsic Lyman-alpha Emission Line Shape Uncertainty

Abstract

Arguably the best hope of understanding the tail end of the reionization of the intergalactic medium (IGM) at redshift z > 6 is through the detection and characterization of the Gunn-Peterson (GP) damping wing absorption of the IGM in bright quasar spectra. However, the use of quasar spectra to measure the IGM damping wing requires a model of the quasar's intrinsic Lyman-alpha emission line. Here we quantify the uncertainties in the intrinsic line shapes, and how those uncertainties affect the determination of the IGM neutral fraction. We have assembled a catalog of high-resolution HST spectra of the emission lines of unobscured low-redshift quasars, and have characterized the variance in the shapes of their lines. We then add simulated absorption from the high-redshift IGM to these quasar spectra in order to determine the corresponding uncertainties in reionization constraints using current and future samples of z > 6 quasar spectra. We find that, if the redshift of the Lyman-alpha emission line is presumed to coincide with the systemic redshift determined from metal lines, the inferred IGM neutral fraction is systematically biased to low values due to a systematic blueshift of the Lyman-alpha line relative to the metal lines. If a similar blueshift persists in quasars at z > 6, this bias strengthens previous claims of a significant neutral hydrogen fraction at z ~ 6. This technique is capable of making a robust distinction between a highly ionized (x_IGM ~ 10^-3) and a neutral (x_IGM = 1) IGM with even a few bright quasars.

accepted for publication in MNRAS, full tables available at http://www.astro.columbia.edu/~roban/

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• Reionization and high-redshift galaxies: the view from quasar absorption lines
• Evidence of Gunn-Peterson damping wings in high-z quasar spectra: strengthening the case for incomplete reionization
• Near-zone sizes and the rest frame extreme ultra-violet spectral index of the highest redshift quasars
• Improved measurements of the intergalactic medium temperature around quasars: possible evidence for the initial stages of He-II reionisation at z~6
• The Epoch of Reionization
• Lyα emission line reconstruction for high-$z$ QSOs
• The Global History of Reionisation
• The Faint End of the z=5 Quasar Luminosity Function from the CFHTLS
• Predicting Quasar Continua Near Lyman-$\alpha$ with Principal Component Analysis
• The Complete Ultraviolet Spectrum of the Archetypal "Wind-Dominated" Quasar Mrk~231: Absorption and Emission from a High-Speed Dusty Nuclear Outflow
• The Surprising Absence of Absorption in the Far-Ultraviolet Spectrum of Mrk 231
• Quasars as probes of cosmological reionization
• Formation of the seed black holes: a role of quark nuggets?
• Deep Learning Prediction of Quasars Broad Ly$\alpha$ Emission Line