New constraints on warm dark matter from the Lyman-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>α</mml:mi></mml:mrow></mml:math> forest power spectrum

Abstract

The forest of Lyman-$\ensuremath{\alpha}$ absorption lines detected in the spectra of distant quasars encodes information on the nature and properties of dark matter and the thermodynamics of diffuse baryonic material. Its main observable---the 1D flux power spectrum (FPS)---should exhibit a suppression on small scales and an enhancement on large scales in warm dark matter (WDM) cosmologies compared to standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$. Here, we present an unprecedented suite of 1080 high-resolution cosmological hydrodynamical simulations run with the graphics processing unit-accelerated code cholla to study the evolution of the Lyman-$\ensuremath{\alpha}$ forest under a wide range of physically motivated gas thermal histories along with different free-streaming lengths of WDM thermal relics in the early Universe. A statistical comparison of synthetic data with the forest FPS measured down to the smallest velocity scales ever probed at redshifts $4.0\ensuremath{\lesssim}z\ensuremath{\lesssim}5.2$ [E. Boera et al., Revealing reionization with the thermal history of the intergalactic medium: New constraints from the $\mathrm{Ly}\ensuremath{\alpha}$ flux power spectrum, Astrophys. J. 872, 101 (2019)] yields a lower-limit ${m}_{\mathrm{WDM}}&gt;3.1\text{ }\text{ }\mathrm{keV}$ (95% C.L.) for the WDM particle mass and constrains the amplitude and spectrum of the photoheating and photoionizing background produced by star-forming galaxies and active galactic nuclei at these redshifts. Interestingly, our Bayesian inference analysis appears to weakly favor WDM models with a peak likelihood value at the thermal relic mass of ${m}_{\mathrm{WDM}}=4.5\text{ }\text{ }\mathrm{keV}$. We find that the suppression of the FPS from free-streaming saturates at $k\ensuremath{\gtrsim}0.1\text{ }\text{ }\mathrm{s}\text{ }{\mathrm{km}}^{\ensuremath{-}1}$ because of peculiar velocity smearing, and this saturated suppression combined with a slightly lower gas temperature provides a moderately better fit to the observed small-scale FPS for WDM cosmologies.

Topics & Concepts