Warmth Elevating the Depths: Shallower Voids with Warm Dark Matter
  Warm dark matter (WDM) has been proposed as an alternative to cold dark
matter (CDM), to resolve issues such as the apparent lack of satellites around
the Milky Way. Even if WDM is not the answer to observational issues, it is
essential to constrain the nature of the dark matter. The effect of WDM on
haloes has been extensively studied, but the small-scale initial smoothing in
WDM also affects the present-day cosmic web and voids. It suppresses the cosmic
"sub-web" inside voids, and the formation of both void haloes and subvoids. In
$N$-body simulations run with different assumed WDM masses, we identify voids
with the ZOBOV algorithm, and cosmic-web components with the ORIGAMI algorithm.
As dark-matter warmth increases (i.e., particle mass decreases), void density
minima grow shallower, while void edges change little. Also, the number of
subvoids decreases. The density field in voids is particularly insensitive to
baryonic physics, so if void density profiles and minima could be measured
observationally, they would offer a valuable probe of the nature of dark
matter. Furthermore, filaments and walls become cleaner, as the substructures
in between have been smoothed out; this leads to a clear, mid-range peak in the
density PDF.
