Kavli Affiliate: Salman Habib
| First 5 Authors: Solène Chabanier, J. D. Emberson, Zarija Lukić, Jesus Pulido, Salman Habib
| Summary:
We compare two state-of-the-art numerical codes to study the overall accuracy
in modeling the intergalactic medium and reproducing Lyman-$alpha$ forest
observables for DESI and high-resolution data sets. The codes employ different
approaches to solving both gravity and modeling the gas hydrodynamics. The
first code, Nyx, solves the Poisson equation using the Particle-Mesh (PM)
method and the Euler equations using a finite volume method. The second code,
CRKHACC, uses a Tree-PM method to solve for gravity, and an improved
Lagrangian smoothed particle hydrodynamics (SPH) technique, where fluid
elements are modeled with particles, to treat the intergalactic gas. We compare
the convergence behavior of the codes in flux statistics as well as the degree
to which the codes agree in the converged limit. We find good agreement overall
with differences being less than observational uncertainties, and a
particularly notable $lesssim$1% agreement in the 1D flux power spectrum.
This agreement was achieved by applying a tessellation methodology for
reconstructing the density in CRKHACC instead of using an SPH kernel as is
standard practice. We show that use of the SPH kernel can lead to significant
and unnecessary biases in flux statistics; this is especially prominent at high
redshifts, $z sim 5$, as the Lyman-$alpha$ forest mostly comes from
lower-density regions which are intrinsically poorly sampled by SPH particles.
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