Spatial and velocity biases 445Figure 15.9.Top panel: The evolution of bias at comoving scale of 0. 54 h−^1 Mpc for halos
with different circular velocities.Bottom panel: Dependence of the bias on the scale for
halos with the same circular velocity.
withvc > 150 km s−^1 was 15 times larger than that of the dark matter at
r = 0. 5 h−^1 Mpc (see figure 8 in Col ́ınet al(1999). The bias was also very
strongly mass-dependent with more massive halos being more clustered. At
smaller redshifts the bias was declining quickly. Aroundz =1–2 (the exact
value depends on the halo circular velocity) the bias crossed unity and became
less than unity (antibias) at later redshifts.
The evolution of bias is illustrated by figure 15.10. The figure shows that,
at all epochs, the overdensity of halos tightly correlates with the overdensity of
the dark matter. The slope of the relation depends on the dark matter density and
evolves with time. Atz>1 halos are biased (δh>δdm) in overdense regions with