Broadband distortion modeling in Lyman-α forest BAO fitting

Michael Blomqvist, David Kirkby, Julian E. Bautista, Andreu Arinyo-I-Prats, Nicolás G. Busca, Jordi Miralda-Escudé, Anže Slosar, Andreu Font-Ribera, Daniel Margala, Donald P. Schneider, Jose A. Vazquez

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Abstract

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 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. 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.

Original languageEnglish (US)
Article number034
JournalJournal of Cosmology and Astroparticle Physics
Volume2015
Issue number11
DOIs
StatePublished - Nov 23 2015

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics

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    Blomqvist, M., Kirkby, D., Bautista, J. E., Arinyo-I-Prats, A., Busca, N. G., Miralda-Escudé, J., Slosar, A., Font-Ribera, A., Margala, D., Schneider, D. P., & Vazquez, J. A. (2015). Broadband distortion modeling in Lyman-α forest BAO fitting. Journal of Cosmology and Astroparticle Physics, 2015(11), [034]. https://doi.org/10.1088/1475-7516/2015/11/034