We present a new bound on the ultralight axion (ULA) dark matter mass m_{a}, using the Lyman-alpha forest to look for suppressed cosmic structure growth: a 95% lower limit m_{a}>2×10^{-20} eV. This ...strongly disfavors (>99.7% credibility) the canonical ULA with 10^{-22} eV<m_{a}<10^{-21} eV, motivated by the string axiverse and solutions to possible tensions in the cold dark matter model. We strengthen previous equivalent bounds by about an order of magnitude. We demonstrate the robustness of our results using an optimized emulator of improved hydrodynamical simulations.
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We set the strongest limits to date on the velocity-independent dark matter (DM)-proton cross section σ for DM masses m=10 keV to 100 GeV, using large-scale structure traced by the Lyman-alpha ...forest: e.g., a 95% lower limit σ<6×10^{-30} cm^{2}, for m=100 keV. Our results complement direct detection, which has limited sensitivity to sub-GeV DM. We use an emulator of cosmological simulations, combined with data from the smallest cosmological scales used to date, to model and search for the imprint of primordial DM-proton collisions. Cosmological bounds are improved by up to a factor of 25.
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We present a general framework for obtaining robust bounds on the nature of dark matter using cosmological N-body simulations and Lyman-alpha forest data. We construct an emulator of hydrodynamical ...simulations, which is a flexible, accurate and computationally efficient model for predicting the response of the Lyman-alpha forest flux power spectrum to different dark matter models, the state of the intergalactic medium (IGM) and the primordial power spectrum. The emulator combines a flexible parametrization for the small-scale suppression in the matter power spectrum arising in "noncold" dark matter models, with an improved IGM model. We then demonstrate how to optimize the emulator for the case of ultralight axion dark matter, presenting tests of convergence. We also carry out cross-validation tests of the accuracy of flux power spectrum prediction. This framework can be optimized for the analysis of many other dark matter candidates, e.g., warm or interacting dark matter. Our work demonstrates that a combination of an optimized emulator and cosmological "effective theories," where many models are described by a single set of equations, is a powerful approach for robust and computationally efficient inference from the cosmic large-scale structure.
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Abstract
Three-dimensional correlations of the Lyman-
α
(Ly
α
) forest and cross correlations between the Ly
α
forest and quasars have been
measured on large scales, allowing a precise measurement of ...the baryon acoustic oscillation (BAO) feature at redshifts
z
> 2.
These 3D correlations are often modelled using linear perturbation theory,
but full-shape analyses to extract cosmological information beyond BAO will
require more realistic models capable of describing non-linearities present at smaller scales.
We present a measurement of the Ly
α
forest flux power spectrum from large
hydrodynamic simulations — the Sherwood simulations — and compare it to different
models describing the small-scale deviations from linear theory.
We confirm that the model presented in Arinyo-i-Prats et al. (2015) fits the measured
3D power up to
k
= 10
h
Mpc
-1
with an accuracy better than 5%, and show that the same
model can also describe the 1D correlations with similar precision.
We also present, for the first time, an equivalent study for the
cross-power spectrum of halos with the Ly
α
forest, and we discuss different challenges
we face when modelling the cross-power spectrum beyond linear scales.
We make all our measured power spectra public in
https://github.com/andreufont/sherwoo_p3d
.
This study is a step towards joint analyses of 1D and 3D flux correlations,
and towards using the quasar-Ly
α
cross-correlation beyond BAO analyses.
Abstract
Interpreting observations of the Lyman-α forest flux power spectrum
requires interpolation between a small number of expensive simulations.
We present a Gaussian process emulator modelling ...the 1D flux power spectrum as
a function of the amplitude and slope of the small-scale linear matter power
spectrum, and the state of the intergalactic medium at the epoch of interest
(2 < z < 4).
This parameterisation enables the prediction of the flux power spectrum in
extended cosmological models that are not explicitly included in the training set,
eliminating the need to construct bespoke emulators for a number of extensions
to ΛCDM.
Our emulator is appropriate for cosmologies in which the linear matter power
spectrum is described to percent level accuracy by just an amplitude and
slope across the epoch of interest, and in the regime probed by eBOSS/DESI data.
We demonstrate this for massive neutrino cosmologies, where the emulator is able
to predict the flux power spectrum in a Σ m
ν
=0.3 eV neutrino cosmology
to sub-percent accuracy, without including massive neutrinos in the training simulations.
Further parameters would be required to describe models with sharp features in the
linear power, such as warm or light axion dark matter.
This work will facilitate the combination of upcoming DESI data
with observations of the
cosmic microwave background, to obtain constraints on neutrino mass and
other extensions to ΛCDM cosmology.
The Lyman-alpha forest provides strong constraints on both cosmological parameters and intergalactic medium astrophysics, which are forecast to improve further with the next generation of surveys ...including eBOSS and DESI. As is generic in cosmological inference, extracting this information requires a likelihood to be computed throughout a high-dimensional parameter space. Evaluating the likelihood requires a robust and accurate mapping between the parameters and observables, in this case the 1D flux power spectrum. Cosmological simulations enable such a mapping, but due to computational time constraints can only be evaluated at a handful of sample points; “emulators” are designed to interpolate between these. The problem then reduces to placing the sample points such that an accurate mapping is obtained while minimising the number of expensive simulations required. To address this, we introduce an emulation procedure that employs Bayesian optimisation of the training set for a Gaussian process interpolation scheme. Starting with a Latin hypercube sampling (other schemes with good space-filling properties can be used), we iteratively augment the training set with extra simulations at new parameter positions which balance the need to reduce interpolation error while focussing on regions of high likelihood. We show that smaller emulator error from the Bayesian optimisation propagates to smaller widths on the posterior distribution. Even with fewer simulations than a Latin hypercube, Bayesian optimisation shrinks the 95% credible volume by 90% and, e.g., the 1σ error on the amplitude of small-scale primordial fluctuations by 38%. This is the first demonstration of Bayesian optimisation applied to large-scale structure emulation, and we anticipate the technique will generalise to many other probes such as galaxy clustering, weak lensing and 21cm.
An emulator for the Lyman-α forest Bird, Simeon; Rogers, Keir K.; Peiris, Hiranya V. ...
Journal of cosmology and astroparticle physics,
02/2019, Volume:
2019, Issue:
2
Journal Article
Peer reviewed
Open access
We present methods for interpolating between the 1-D flux power spectrum of the Lyman-α forest, as output by cosmological hydrodynamic simulations. Interpolation is necessary for cosmological ...parameter estimation due to the limited number of simulations possible. We construct an emulator for the \Lya forest flux power spectrum from 21 small simulations using Latin hypercube sampling and Gaussian process interpolation. We show that this emulator has a typical accuracy of 1.5% and a worst-case accuracy of 4%, which compares well to the current statistical error of 3–5% at z<3 from BOSS DR9. We compare to the previous state of the art, quadratic polynomial interpolation. The Latin hypercube samples the entire volume of parameter space, while quadratic polynomial emulation samples only lower-dimensional subspaces. The Gaussian process provides an estimate of the emulation error and we show using test simulations that this estimate is reasonable. We construct a likelihood function and use it to show that the posterior constraints generated using the emulator are unbiased. We show that our Gaussian process emulator has lower emulation error than quadratic polynomial interpolation and thus produces tighter posterior confidence intervals, which will be essential for future Lyman-α surveys such as DESI.
ABSTRACT
Gravitational weak lensing by dark matter haloes leads to a measurable imprint in the shear correlation function of galaxies. Fuzzy dark matter (FDM), composed of ultralight axion-like ...particles of mass m ∼ 10−22 eV, suppresses the matter power spectrum and shear correlation with respect to standard cold dark matter. We model the effect of FDM on cosmic shear using the optimized halo model HMCode, accounting for additional suppression of the mass function and halo concentration in FDM as observed in N-body simulations. We combine Dark Energy Survey Year 1 (DES-Y1) data with the Planck cosmic microwave background anisotropies to search for shear correlation suppression caused by FDM. We find no evidence of suppression compared to the preferred cold dark matter model, and thus set a new lower limit to the FDM particle mass. Using a log-flat prior and marginalizing over uncertainties related to the non-linear model of FDM, we find a new, independent 95 per cent C.L. lower limit log10m > −23 combining Planck and DES-Y1 shear, an improvement of almost two orders of magnitude on the mass bound relative to CMB-only constraints. Our analysis is largely independent of baryonic modelling, and of previous limits to FDM covering this mass range. Our analysis highlights the most important aspects of the FDM non-linear model for future investigation. The limit to FDM from weak lensing could be improved by up to three orders of magnitude with $\mathcal {O}(0.1)$ arcmin cosmic shear angular resolution, if FDM and baryonic feedback can be simultaneously modelled to high precision in the halo model.
Abstract
We test a method to reduce unwanted sample variance when predicting Ly
α
forest power spectra from cosmological hydrodynamical simulations. Sample variance arises due to sparse sampling of ...modes on large scales and propagates to small scales through nonlinear gravitational evolution. To tackle this, we generate initial conditions in which the density perturbation amplitudes are fixed to the ensemble average power spectrum—and are generated in pairs with exactly opposite phases. We run 50 such simulations (25 pairs) and compare their performance against 50 standard simulations by measuring the Ly
α
1D and 3D power spectra at redshifts
z
= 2, 3, and 4. Both ensembles use periodic boxes of
40
h
−
1
Mpc
containing 512
3
particles each of dark matter and gas. As a typical example of improvement, for wavenumbers
k
=
0.25
h
Mpc
−
1
at
z
= 3, we find estimates of the 1D and 3D power spectra converge 34 and 12 times faster in a paired–fixed ensemble compared with a standard ensemble. We conclude that, by reducing the computational time required to achieve fixed accuracy on predicted power spectra, the method frees up resources for exploration of varying thermal and cosmological parameters—ultimately allowing the improved precision and accuracy of statistical inference.
Abstract
We measure the effect of high column density absorbing systems of neutral hydrogen (H i) on the one-dimensional (1D) Lyman α forest flux power spectrum using cosmological hydrodynamical ...simulations from the Illustris project. High column density absorbers (which we define to be those with H i column densities $N({\rm H}\, \small {I}) > 1.6 \times 10^{17}\, \mathrm{atoms}\, \mathrm{cm}^{-2}$) cause broadened absorption lines with characteristic damping wings. These damping wings bias the 1D Lyman α forest flux power spectrum by causing absorption in quasar spectra away from the location of the absorber itself. We investigate the effect of high column density absorbers on the Lyman α forest using hydrodynamical simulations for the first time. We provide templates as a function of column density and redshift, allowing the flexibility to accurately model residual contamination, i.e. if an analysis selectively clips out the largest damping wings. This flexibility will improve cosmological parameter estimation, for example, allowing more accurate measurement of the shape of the power spectrum, with implications for cosmological models containing massive neutrinos or a running of the spectral index. We provide fitting functions to reproduce these results so that they can be incorporated straightforwardly into a data analysis pipeline.
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