UV background fluctuations and threepoint correlations in the largescale clustering of the Lyman α forest
Abstract
Using the Lyman α (Lyα) Mass Association Scheme, we make theoretical predictions for the threedimensional threepoint correlation function (3PCF) of the Lyα forest at redshift z = 2.3. We bootstrap results from the (100 h^{1} Mpc)^{3} Horizon hydrodynamic simulation to a (1 h^{1} Gpc)^{3}Nbody simulation, considering both a uniform ultraviolet background (UVB) and a fluctuating UVB sourced by quasars with a comoving n_{q} ≈ 10^{5}h^{3} Mpc^{3} placed either in massive haloes or randomly. On scales of 1030 h^{1} Mpc, the flux 3PCF displays hierarchical scaling with the square of the twopoint correlation function (2PCF), but with an unusual value of Q ≡ ζ_{123}/(ξ_{12}ξ_{13} + ξ_{12}ξ_{23} + ξ_{13}ξ_{23}) ≈ 4.5 that reflects the low bias of the Lyα forest and the anticorrelation between mass density and transmitted flux. For halobased quasars and an ionizing photon mean free path of λ = 300 h^{1} Mpc comoving, UVB fluctuations moderately depress the 2PCF and 3PCF, with cancelling effects on Q. For λ = 100 or 50 h^{1} Mpc, UVB fluctuations substantially boost the 2PCF and 3PCF on large scales, shifting the hierarchical ratio to Q ≈ 3. We scale our simulation results to derive rough estimate of the detectability of the 3PCF in current and future observational data sets for the redshift range z = 2.12.6. At r = 10 and 20 h^{1} Mpc, we predict a signaltonoise ratio (SNR) of ∼9 and ∼7, respectively, for both Baryon Oscillation Spectroscopic Survey (BOSS) and extended BOSS (eBOSS), and ∼37 and ∼25 for Dark Energy Spectroscopic Instrument (DESI). At r = 40 h^{1} Mpc the predicted SNR is lower by a factor of ∼35. Measuring the flux 3PCF would provide a novel test of the conventional paradigm of the Lyα forest and help separate the contributions of UVB fluctuations and density fluctuations to Lyα forest clustering, thereby solidifying its foundation as a tool of precision cosmology.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 August 2019
 DOI:
 10.1093/mnras/stz1632
 arXiv:
 arXiv:1905.02208
 Bibcode:
 2019MNRAS.487.5346T
 Keywords:

 intergalactic medium;
 cosmology: theory;
 largescale structure of Universe;
 ultraviolet: general;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Submitted to MNRAS. 19 pages, 17 figures