A slice of gas density through a cosmological volume, based on a composite taken from multiple numerical simulations, each based on a different assumption of the nature of dark matter. The horizontal direction indicates time: redshift decreases from five to zero, from left to right, while the time since the Big Bang similarly increases from one, to fourteen, billion years. Such a view is similar to a "lightcone", which transforms a periodic cosmological box simulation, each box saved at a discrete time, into a volume which extends across a cosmological distance. In this visualization, the vertical direction indicates increasing mass of a putative warm dark matter (WDM) particle, from the cold dark matter (CDM, infinite mass) case at the bottom, to 0.3 keV at the top. As the WDM particle mass changes so does the amount of free-streaming, which has the effect of suppressing the formation of small-scale structure. This makes the large-scale cosmic web appear smoother near the top of the image, relative to the bottom.
Methods: CHOLLA code