Novel constraints on non-cold (non-thermal) Dark Matter from Lyman-$\alpha$ forest data

TL;DR

This paper introduces a flexible method to constrain various non-cold dark matter models using Lyman-alpha forest data, providing new limits on dark matter properties and testing multiple scenarios without extensive simulations.

Contribution

The authors develop a novel parametrisation and interpolation scheme enabling constraints on diverse nCDM models from Lyman-alpha data without running specific simulations.

Findings

Upper limit on power suppression scale: α<0.03 Mpc/h (2σ C.L.)

Mild tension between thermal warm DM models and data (~2σ C.L.)

Mixed warm and cold DM models are also in tension with observations

Abstract

In this paper we present an efficient method for constraining both thermal and non-thermal Dark Matter (DM) scenarios with the Lyman-$\alpha$ forest, based on a simple and flexible parametrisation capable to reproduce the small scale clustering signal of a large set of non-cold DM (nCDM) models. We extract new limits on the fundamental DM properties, through an extensive analysis of the high resolution, high redshift data obtained by the MIKE/HIRES spectrographs. By using a large suite of hydrodynamical simulations, we determine constraints on both astrophysical, cosmological, and nCDM parameters by performing a full Monte Carlo Markov Chain (MCMC) analysis. We obtain a marginalised upper limit on the largest possible scale at which a power suppression induced by nearly any nCDM scenario can occur, i.e. $\alpha<0.03~{\rm{Mpc}}/h$ (2$\sigma$ C.L.). We explicitly describe how to test several of the most viable nCDM scenarios without the need to run any specific numerical simulations, due to the novel parametrisation proposed, and due to a new scheme that interpolates between the cosmological models explored. The shape of the linear matter power spectrum for standard thermal warm DM models appear to be in mild tension ($\sim 2\sigma$ C.L.) with the data, compared to non-thermal scenarios. We show that a DM fluid composed by both a warm (thermal) and a cold component is also in tension with the Lyman-$\alpha$ forest, at least for large $\alpha$ values. This is the first study that allows to probe the linear small scale shape of the DM power spectrum for a large set of nCDM models.