Papers › Cosmological Constraints from the eBOSS Lyman-α Forest using the PRIYA Simulations
Cosmological Constraints from the eBOSS Lyman-α Forest using the PRIYA Simulations
M. A. Fernandez, Simeon Bird, Ming-Feng Ho
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We present new cosmological parameter constraints from the eBOSS Lyman-α forest survey. We use a new theoretical model and likelihood based on the PRIYA simulation suite. PRIYA is the first suite to resolve the Lyman-α forest in a ($120$~Mpc/h~)³ volume, using a multi-fidelity emulation technique. We use PRIYA to predict Lyman-α forest observables with ≲1% interpolation error over an $11$ dimensional ($9$ simulated, $2$ in post-processing) parameter space. We identify an internal tension within the flux power spectrum data. Once the discrepant data is removed, we find the primeval scalar spectral index measured at a pivot scale of k₀ = 0.78 Mpc⁻¹ to be n_P = 1.009^(+0.027)_(-0.018) at 68\% confidence. This measurement from the Lyman-α forest flux power spectrum alone is in reasonable agreement with Planck, and in tension with earlier eBOSS analyses. The amplitude of matter fluctuations is σ₈ = 0.733^(+0.026)_(-0.029) at 68\% confidence, in agreement with Dark Energy Survey weak lensing measurements and other small-scale structure probes and in tension with CMB measurements from Planck and ACT. The effective optical depth to Lyman-α photons from our pipeline is in good agreement with earlier high resolution measurements. We find a linear power at z=3 and k = 0.009 s/km of Δ_L² = 0.302^(+0.024)_(-0.027) with a slope n_(eff) = -2.264^(+0.026)_(-0.018). Our flux power spectrum only chains prefer a low level of heating during helium reionization. When we add IGM temperature data we find n_P = 0.983±0.020 and σ₈ = 0.703^(+0.023)_(-0.027). Our chains prefer an early and long helium reionization event, as suggested by measurements from the helium Lyman-α forest. In the near future we will use our pipeline to infer cosmological parameters from the DESI Lyman-α data.
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