Kavli Affiliate: George Efstathiou
| First 5 Authors: Tibor Dome, Simon May, Alex Laguë, David J. E. Marsh, Sarah Johnston
| Summary:
We study the implications of relaxing the requirement for ultralight axions
to account for all dark matter in the Universe by examining mixed dark matter
(MDM) cosmologies with axion fractions $f leq 0.3$ within the fuzzy dark
matter (FDM) window $10^{-25}$ eV $lesssim m lesssim 10^{-23}$ eV. Our
simulations, using a new MDM gravity solver implemented in AxiREPO, capture
wave dynamics across various scales with high accuracy down to redshifts
$zapprox 1$. We identify halos with Rockstar using the CDM component and find
good agreement of inferred halo mass functions (HMFs) and concentration-mass
relations with theoretical models across redshifts $z=1-10$. This justifies our
halo finder approach a posteriori as well as the assumptions underlying the MDM
halo model AxionHMcode. Using the inferred axion halo mass – cold halo mass
relation $M_{text{a}}(M_{text{c}})$ and calibrating a generalised smoothing
parameter $alpha$ to our MDM simulations, we present a new version of
AxionHMcode. The code exhibits excellent agreement with simulations on scales
$k< 20 h$ cMpc$^{-1}$ at redshifts $z=1-3.5$ for $fleq 0.1$ around the
fiducial axion mass $m = 10^{-24.5}$ eV $ = 3.16times 10^{-25}$ eV, with
maximum deviations remaining below 10%. For axion fractions $fleq 0.3$, the
model maintains accuracy with deviations under 20% at redshifts $zapprox 1$
and scales $k< 10 h$ cMpc$^{-1}$, though deviations can reach up to 30% for
higher redshifts when $f=0.3$. Reducing the run-time for a single evaluation of
AxionHMcode to below $1$ minute, these results highlight the potential of
AxionHMcode to provide a robust framework for parameter sampling across MDM
cosmologies in Bayesian constraint and forecast analyses.
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