Abstract
The forest of Lyman-$\alpha$ 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 $Łambda$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-$\alpha$ 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 $4.0z5.2$ (Boera et al. 2019) yields a lower limit
$m_WDM>3.1$ keV (95 percent CL) 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 best-fit thermal relic mass of $m_\rm
WDM=4.5_-1.4^+45$ keV (95 percent CL). We find that the suppression of the
FPS from free-streaming saturates at $k0.1\,$s km$^-1$ 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.
Users
Please
log in to take part in the discussion (add own reviews or comments).