UV background fluctuations and three-point correlations in the large-scale clustering of the Lyman α forest

Journal Article · Tue Jun 18 00:00:00 EDT 2019 · Monthly Notices of the Royal Astronomical Society

DOI:https://doi.org/10.1093/mnras/stz1632· OSTI ID:1611661

Tie, Suk Sien  ^[1]; Weinberg, David H. ^[2]; Martini, Paul ^[2]; Zhu, Wei ^[3]; Peirani, Sébastien ^[4]; Suarez, Teresita ^[5]; Colombi, Stéphane ^[6]

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1. Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
2. Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA; Center for Cosmology and AstroParticle Physics, The Ohio State University, 191 W. Woodruff Avenue, Columbus, OH 43210, USA
3. Canadian Institute for Theoretical Astrophysics (CITA), University of Toronto, 60 St George Street, Toronto, ON M5S 3H8, Canada
4. Institut d’Astrophysique de Paris, CNRS & UPMC, UMR 7095, 98 bis Boulevard Arago, F-75014 Paris, France; Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 75016 Paris, France
5. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK; Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
6. Institut d’Astrophysique de Paris, CNRS & UPMC, UMR 7095, 98 bis Boulevard Arago, F-75014 Paris, France

Using the Lyman α (Lyα) Mass Association Scheme, we make theoretical predictions for the three-dimensional three-point 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)³N-body simulation, considering both a uniform ultraviolet background (UVB) and a fluctuating UVB sourced by quasars with a comoving n_q ≈ 10^-5h³ Mpc^-3 placed either in massive haloes or randomly. On scales of 10–30 h^-1 Mpc, the flux 3PCF displays hierarchical scaling with the square of the two-point correlation function (2PCF), but with an unusual value of Q ≡ ζ₁₂₃/(ξ₁₂ξ₁₃ + ξ₁₂ξ₂₃ + ξ₁₃ξ₂₃) ≈ -4.5 that reflects the low bias of the Lyα forest and the anticorrelation between mass density and transmitted flux. For halo-based 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 = 2.1–2.6. At r = 10 and 20 h^-1 Mpc, we predict a signal-to-noise 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 ~3–5. 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.

• Research Organization: The Ohio State Univ., Columbus, OH (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: SC0011726
• OSTI ID: 1611661
• Journal Information: Monthly Notices of the Royal Astronomical Society, Vol. 487, Issue 4; ISSN 0035-8711
• Publisher: Royal Astronomical Society
• Country of Publication: United States
• Language: English

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