Identifying clustering at high redshift through actively star-forming
  galaxies
  Identifying galaxy clustering at high redshift (i.e. z > 1) is essential to
our understanding of the current cosmological model. However, at increasing
redshift, clusters evolve considerably in star-formation activity and so are
less likely to be identified using the widely-used red sequence method. Here we
assess the viability of instead identifying high redshift clustering using
actively star-forming galaxies (SMGs associated with over-densities of
BzKs/LBGs). We perform both a 2- and 3-D clustering analysis to determine
whether or not true (3D) clustering can be identified where only 2D data are
available. As expected, we find that 2D clustering signals are weak at best and
inferred results are method dependant. In our 3D analysis, we identify 12 SMGs
associated with an over-density of galaxies coincident both spatially and in
redshift - just 8% of SMGs with known redshifts in our sample. Where an SMG in
our target fields lacks a known redshift, their sightline is no more likely to
display clustering than blank sky fields; prior redshift information for the
SMG is required to identify a true clustering signal. We find that the strength
of clustering in the volume around typical SMGs, while identifiable, is not
exceptional. However, we identify a small number of highly clustered regions,
all associated with an SMG. The most notable of these, surrounding
LESSJ033336.8-274401, potentially contains an SMG, a QSO and 36 star-forming
galaxies (a > 20sig over-density) all at z~1.8. This region is highly likely to
represent an actively star-forming cluster and illustrates the success of using
star-forming galaxies to select sites of early clustering. Given the increasing
number of deep fields with large volumes of spectroscopy, or high quality and
reliable photometric redshifts, this opens a new avenue for cluster
identification in the young Universe.
