The Lyman-alpha forest in three dimensions: measurements of large scale flux correlations from BOSS 1st-year data

TL;DR

This paper measures three-dimensional flux correlations in the Lyman-alpha forest using BOSS data, detecting large-scale structures and redshift-space distortions, and constrains cosmological parameters within a standard LCDM model.

Contribution

First detection of flux correlations across widely separated sightlines in the Lyman-alpha forest and measurement of redshift-space distortions using BOSS data.

Findings

Flux correlations detected out to 60 Mpc/h separations.

Redshift-space distortion parameter beta constrained between 0.44 and 1.20.

Bias parameter b constrained between 0.16 and 0.24.

Abstract

Using a sample of approximately 14,000 z>2.1 quasars observed in the first year of the Baryon Oscillation Spectroscopic Survey (BOSS), we measure the three-dimensional correlation function of absorption in the Lyman-alpha forest. The angle-averaged correlation function of transmitted flux (F = exp(-tau)) is securely detected out to comoving separations of 60 Mpc/h, the first detection of flux correlations across widely separated sightlines. A quadrupole distortion of the redshift-space correlation function by peculiar velocities, the signature of the gravitational instability origin of structure in the Lyman-alpha forest, is also detected at high significance. We obtain a good fit to the data assuming linear theory redshift-space distortion and linear bias of the transmitted flux, relative to the matter fluctuations of a standard LCDM cosmological model (inflationary cold dark matter with a cosmological constant). At 95% confidence, we find a linear bias parameter 0.16<b<0.24 and redshift-distortion parameter 0.44<beta<1.20, at central redshift z=2.25, with a well constrained combination b(1+\beta)=0.336 +/- 0.012. The errors on beta are asymmetric, with beta=0 excluded at over 5 sigma confidence level. The value of beta is somewhat low compared to theoretical predictions, and our tests on synthetic data suggest that it is depressed (relative to expectations for the Lyman-alpha forest alone) by the presence of high column density systems and metal line absorption. These results set the stage for cosmological parameter determinations from three-dimensional structure in the Lyman-alpha forest, including anticipated constraints on dark energy from baryon acoustic oscillations.