On merger bias and the clustering of quasars
  We use the large catalogues of haloes available for the Millennium Simulation
to test whether recently merged haloes exhibit stronger large-scale clustering
than other haloes of the same mass. This effect could help to understand the
very strong clustering of quasars at high redshift. However, we find no
statistically significant excess bias for recently merged haloes over the
redshift range 2 < z < 5, with the most massive haloes showing an excess of at
most ~5%. We also consider galaxies extracted from a semianalytic model built
on the Millennium Simulation. At fixed stellar mass, we find an excess bias of
~ 20-30% for recently merged objects, decreasing with increasing stellar mass.
The fact that recently-merged galaxies are found in systematically more massive
haloes than other galaxies of the same stellar mass accounts for about half of
this signal, and perhaps more for high-mass galaxies. The weak merger bias of
massive systems suggests that objects of merger-driven nature, such as quasars,
do not cluster significantly differently than other objects of the same
characteristic mass. We discuss the implications of these results for the
interpretation of clustering data with respect to quasar duty cycles,
visibility times, and evolution in the black hole-host mass relation.
