Broadband distortion modeling in Lyman-α forest BAO fitting

Apr 24, 2015
30 pages
Published in:
  • JCAP 11 (2015) 034
  • Published: Nov 23, 2015
e-Print:

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Abstract: (IOP)
In recent years, the Lyman-α absorption observed in the spectra of high-redshift quasars has been used as a tracer of large-scale structure by means of the three-dimensional Lyman-α forest auto-correlation function at redshift zsimeq 2.3, but the need to fit the quasar continuum in every absorption spectrum introduces a broadband distortion that is difficult to correct and causes a systematic error for measuring any broadband properties. We describe a k-space model for this broadband distortion based on a multiplicative correction to the power spectrum of the transmitted flux fraction that suppresses power on scales corresponding to the typical length of a Lyman-α forest spectrum. Implementing the distortion model in fits for the baryon acoustic oscillation (BAO) peak position in the Lyman-α forest auto-correlation, we find that the fitting method recovers the input values of the linear bias parameter bF and the redshift-space distortion parameter βF for mock data sets with a systematic error of less than 0.5%. Applied to the auto-correlation measured for BOSS Data Release 11, our method improves on the previous treatment of broadband distortions in BAO fitting by providing a better fit to the data using fewer parameters and reducing the statistical errors on βF and the combination bF(1+βF) by more than a factor of seven. The measured values at redshift z=2.3 are βF=1.39(+0.11)( )(+0.24)( )(+0.38)(−)(0.10)( )(−)(0.19)( )(−)(0.28) and bF(1+βF)=−0.374(+0.007)( )(+0.013)( )(+0.020)(−)(0.007)( )(−)(0.014)( )(−)(0.022) (1σ, 2σ and 3σ statistical errors). Our fitting software and the input files needed to reproduce our main results are publicly available.
Note:
  • 28 pages, 15 figures, matches the published version
  • dark energy experiments
  • Lyman alpha forest
  • cosmological parameters from LSS
  • baryon acoustic oscillations