The one-dimensional Ly-alpha forest power spectrum from BOSS
Nathalie Palanque-Delabrouille, Christophe Yèche, Arnaud Borde, Jean-Marc Le Goff, Graziano Rossi, Matteo Viel, Éric Aubourg, Stephen Bailey, Julian Bautista, Michael Blomqvist, Adam Bolton, James S. Bolton, Nicolás G. Busca, Bill Carithers, Rupert A. C. Croft, Kyle S. Dawson, Timothée Delubac, Andreu Font-Ribera, Shirley Ho, David Kirkby, Khee-Gan Lee, Daniel Margala, Jordi Miralda-Escudé, Demitri Muna, Adam D. Myers, Pasquier Noterdaeme, Isabelle Pâris, Patrick Petitjean, Matthew M. Pieri, James Rich, Emmanuel Rollinde, Nicholas P. Ross, David J. Schlegel, Donald P. Schneider, Anže Slosar, David H. Weinberg
TL;DR
This paper tackles measuring the one-dimensional transmitted-flux power spectrum $P_{1D}(k_{\\parallel})$ of the Lyα forest from a large SDSS-III/BOSS DR9 quasar sample to constrain high-redshift cosmology. It develops two independent pipelines, based on a Fourier transform and a maximum-likelihood estimator, and applies them to 13,821 quasar spectra spanning $<z>\approx 2.2$--$4.4$ and scales $0.001~(\\mathrm{km\\,s^{-1}})^{-1}$ to $0.02~(\\mathrm{km\\,s^{-1}})^{-1}$. The methods show consistency after careful modeling of noise and instrument resolution, enabling an absolute $P_{1D}$ measurement and a quantitative assessment of systematic uncertainties. Using hydrodynamical simulations for interpretation, the study achieves a factor of 2–3 improvement in cosmological precision over previous SDSS results, and in a ΛCDM framework with external $H_0$ constraints finds $\\sigma_8 = 0.83 \\pm 0.03$ and $n_s = 0.97 \\pm 0.02$ from HI absorption in $2.1<z<3.7$.
Abstract
We have developed two independent methods to measure the one-dimensional power spectrum of the transmitted flux in the Lyman-$α$ forest. The first method is based on a Fourier transform, and the second on a maximum likelihood estimator. The two methods are independent and have different systematic uncertainties. The determination of the noise level in the data spectra was subject to a novel treatment, because of its significant impact on the derived power spectrum. We applied the two methods to 13,821 quasar spectra from SDSS-III/BOSS DR9 selected from a larger sample of over 60,000 spectra on the basis of their high quality, large signal-to-noise ratio, and good spectral resolution. The power spectra measured using either approach are in good agreement over all twelve redshift bins from $<z> = 2.2$ to $<z> = 4.4$, and scales from 0.001 $\rm(km/s)^{-1}$ to $0.02 \rm(km/s)^{-1}$. We determine the methodological and instrumental systematic uncertainties of our measurements. We provide a preliminary cosmological interpretation of our measurements using available hydrodynamical simulations. The improvement in precision over previously published results from SDSS is a factor 2--3 for constraints on relevant cosmological parameters. For a $Λ$CDM model and using a constraint on $H_0$ that encompasses measurements based on the local distance ladder and on CMB anisotropies, we infer $σ_8 =0.83\pm0.03$ and $n_s= 0.97\pm0.02$ based on \ion{H}{i} absorption in the range $2.1<z<3.7$.