The Secondary Spin Bias of Dark Matter Haloes
  We investigate the role of angular momentum in the clustering of dark matter
haloes. We make use of data from two high-resolution N-body simulations
spanning over four orders of magnitude in halo mass, from $10^{9.8}$ to
$10^{14}\ h^{-1}\ \text{M}_\odot$. We explore the hypothesis that mass
accretion in filamentary environments alters the angular momentum of a halo,
thereby driving a correlation between the spin parameter $\lambda$ and the
strength of clustering. However, we do not find evidence that the distribution
of matter on large scales is related to the spin of haloes. We find that a
halo's spin is correlated with its age, concentration, sphericity, and mass
accretion rate. Removing these correlations strongly affects the strength of
secondary spin bias at low halo masses. We also find that high spin haloes are
slightly more likely to be found near another halo of comparable mass. These
haloes that are found near a comparable mass neighbour - a \textit{twin} - are
strongly spatially biased. We demonstrate that this \textit{twin bias}, along
with the relationship between spin and mass accretion rates, statistically
accounts for halo spin secondary bias.
