Date Published:

September 1, 201

Abstract:

The Lyman-β forest refers to a region in the spectra of distantquasars that lies between the rest-frame Lyman-β and Lyman-γemissions. The forest in this region is dominated by a combination ofabsorption due to resonant Lyα and Lyβ scattering. Whenconsidering the 1D Lyβ forest in addition to the 1D Lyαforest, the full statistical description of the data requires four 1Dpower spectra: Lyα and Lyβ auto-power spectra and theLyα-Lyβ real and imaginary cross-power spectra. We describehow these can be measured using an optimal quadratic estimator thatnaturally disentangles Lyα and Lyβ contributions. Using asample of approximately 60,000 quasar sight-lines from the BOSS DataRelease 9, we make the measurement of the one-dimensional power spectrumof fluctuations due to the Lyβ resonant scattering. While we havenot corrected our measurements for resolution damping of the power andother systematic effects carefully enough to use them for cosmologicalconstraints, we can robustly conclude the following: i) Lyβ powerspectrum and Lyα-Lyβ cross spectra are detected with highstatistical significance; ii) the cross-correlation coefficient is ≈1 on large scales; iii) the Lyβ measurements are contaminated bythe associated OVI absorption, which is analogous to the SiIIIcontamination of the Lyα forest. Measurements of the Lyβforest will allow extension of the usable path-length for the Lyαmeasurements while allowing a better understanding of the physics ofintergalactic medium and thus more robust cosmological constraints.

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