DEMNUni: The clustering of large-scale structures in the presence of massive neutrinos

TL;DR

DEMNUni investigates nonlinear large-scale structure in massive-neutrino cosmologies using 8 $h^{-3}$Gpc$^3$ volume simulations with neutrinos as a separate fluid. The main finding is that nonlinear evolution is dominated by the CDM component, enabling accurate predictions of the total matter power spectrum by evolving only the CDM nonlinearity and adding linear neutrino terms; Halofit calibrated on $\Lambda$CDM can be applied to the linear CDM spectrum to predict $P_{mm}$ with comparable accuracy, while halo statistics require defining bias with respect to cold matter. The work also shows that neglecting neutrino effects in redshift-space distortion modeling can bias growth-rate measurements by about 1–2% at $z\lesssim 1$, highlighting the need for proper accounting in future surveys like Euclid. DEMNUni provides a benchmark set of simulations across four neutrino masses, supporting improved modeling of halo abundances via $\sigma_{cc}$ and of halo clustering in redshift space, and offering a robust resource for testing cosmological inferences in massive-neutrino cosmologies.

Abstract

(abridged) We analyse the clustering features of Large Scale Structures (LSS) in the presence of massive neutrinos, employing a set of large-volume, high-resolution cosmological N-body simulations, where neutrinos are treated as a separate collisionless fluid. The volume of 8$\cGpc$, combined with a resolution of about $8\times 10^{10}\Ms$ for the cold dark matter (CDM) component, represents a significant improvement over previous N-body simulations in massive neutrino cosmologies. We show that most of the nonlinear evolution is generated exclusively by the CDM component. We find that accounting only for the nonlinear evolution of the CDM power spectrum allows to recover the total matter power spectrum with the same accuracy as the massless case. Indeed, we show that, the most recent version of the \halofit\ formula calibrated on $Λ$CDM simulations can be applied directly to the linear CDM power spectrum without requiring additional fitting parameters in the massive case. As a second step, we study the abundance and clustering properties of CDM halos, confirming that, in massive neutrino cosmologies, the proper definition of the halo bias should be made with respect to the {\em cold} rather than the {\em total} matter distribution, as recently shown in the literature. Here we extend these results to the redshift space, finding that, when accounting for massive neutrinos, an improper definition of the linear bias can lead to a systematic error of about 1-$2 \%$ in the determination of the linear growth rate from anisotropic clustering. This result is quite important if we consider that future spectroscopic galaxy surveys, as \eg\ Euclid, are expected to measure the linear growth-rate with statistical errors less than about $3 \%$ at $z\lesssim1$.

Figures (14)

• Figure 1: Linear theory results in massive neutrino cosmologies. Left panel: Ratio of the total matter power spectrum to the CDM power spectrum at redshifts $z=0$ ( continuous curves) and $z=2$ ( dashed curves) for two different values of the sum of neutrino masses, $\Sigma \, m_\nu$$=0.3$ eV in red and $\Sigma \, m_\nu$$=0.53$ eV in green. Dotted lines denote the asymptotic value at small scales of $(1-f_\nu)^2$. Right panel: ratio at $z=0$ of the total matter power spectrum ( continuous curves) and CDM power spectrum ( dashed curves) for the same two cosmologies to the $\Lambda$CDM prediction.
• Figure 2: Comparison between the DEMNUni runs and previous, recent simulations of massive neutrino cosmologies in terms of CDM particle mass resolution and simulation volume. Grey diagonal lines indicate the number of CDM particles.
• Figure 3: Comparison between the different contributions to the nonlinear matter power spectrum, $(1-f_\nu)^2\,P_{cc}$ ( dashed curves), $f_\nu^2\,P_{\nu\nu}$ ( dotted) and $2\,f_\nu\,(1-f_\nu)\,P_{c\nu}$ ( dot-dashed), as described in the text. All the measurements at redshifts $z=0,\,1,\,2$ are shown with shades varying, respectively, from blue to red. Thin coloured curves correspond to the respective linear predictions. Dashed and dotted grey lines on the top panels show the shot-noise contributions to the CDM and neutrinos power spectra. The shaded area in the bottom panel shows values below the 1-$\sigma$, relative, Gaussian uncertainty on $\Delta P(k)/P(k)=1/\sqrt{2\pi k^2/k_f^2}$, $k_f$ being the fundamental frequency of the simulation box.
• Figure 4: Same as figure \ref{['fig:psnlA']}, but for $\Sigma \, m_\nu$$=0.3,\,0.53$ eV.
• Figure 5: Perturbation Theory predictions for the cold matter power spectrum $P_{cc}(k)$. Each panel shows the measurements from the N-body simulations, divided by the reference power spectrum given by the two-loop, standard PT results ( black points with error-bars). Also shown are the corresponding ratios for the linear ( green, dotted), one-loop, standard PT ( blue, thin, dashed curve), multi-point propagator expansion at one- ( red, thick, dashed) and two-loops ( red, thick, continuous) ass obtained from the RegPT code of TaruyaEtal2012.