Broadband distortion modeling in Lyman-α forest BAO fitting

• Published in: Journal of cosmology and astroparticle physics 2015-11, Vol.2015 (11), p.34-34
• Main Authors: Blomqvist, Michael, Kirkby, David, Bautista, Julian E., Arinyo-i-Prats, Andreu, Busca, Nicolás G., Miralda-Escudé, Jordi, Slosar, Anže, Font-Ribera, Andreu, Margala, Daniel, Schneider, Donald P., Vazquez, Jose A.
• Format: Article
• Language: English
• Subjects: ASTRONOMY AND ASTROPHYSICS; Astrophysics; baryon acoustic oscillations; cosmological parameters from LSS; dark energy experiments; Lyman alpha forest; Physics
• ISSN: 1475-7516; 1475-7508; 1475-7516
• DOI: 10.1088/1475-7516/2015/11/034

Recently, 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 z≃ 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. Here, 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. In 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.