A multiscale approach to environment
  Physical processes influencing the properties of galaxies can be traced by
the dependence and evolution of galaxy properties on their environment. A
detailed understanding of this dependence can only be gained through comparison
of observations with models, with an appropriate quantification of the rich
parameter space describing the environment of the galaxy. We present a new,
multiscale parameterization of galaxy environment which retains an
observationally motivated simplicity whilst utilizing the information present
on different scales. We examine how the distribution of galaxy (u-r) colours in
the Sloan Digital Sky Survey (SDSS), parameterized using a double gaussian (red
plus blue peak) fit, depends upon multiscale density. This allows us to probe
the detailed dependence of galaxy properties on environment in a way which is
independent of the halo model. Nonetheless, cross-correlation with the group
catalogue constructed by Yang et al, 2007 shows that galaxy properties trace
environment on different scales in a way which mimics that expected within the
halo model. This provides independent support for the existence of virialized
haloes, and important additional clues to the role played by environment in the
evolution of the galaxy population. This work is described in full by Wilman et
al., 2010, MNRAS, accepted
