Establishing a New Technique for Discovering Large-Scale Structure Using
  the ORELSE Survey
  The Observations of Redshift Evolution in Large Scale Environments (ORELSE)
survey is an ongoing imaging and spectroscopic campaign initially designed to
study the effects of environment on galaxy evolution in high-redshift
($z\sim1$) large-scale structures. We use its rich data in combination with a
powerful new technique, Voronoi tessellation Monte-Carlo (VMC) mapping, to
search for serendipitous galaxy overdensities at $0.55 < z < 1.37$ within 15
ORELSE fields, a combined spectroscopic footprint of $\sim$1.4 square degrees.
Through extensive tests with both observational data and our own mock galaxy
catalogs, we optimize the method's many free parameters to maximize its
efficacy for general overdensity searches. Our overdensity search yielded 402
new overdensity candidates with precisely measured redshifts and an
unprecedented sensitivity down to low total overdensity masses
($\mathcal{M}_{tot} \gtrsim 5\times 10^{13} M_{\odot}$). Using the mock
catalogs, we estimated the purity and completeness of our overdensity catalog
as a function of redshift, total mass, and spectroscopic redshift fraction,
finding impressive levels of both 0.92/0.83 and 0.60/0.49 for
purity/completeness at $z=0.8$ and $z=1.2$, respectively, for all overdensity
masses at spectroscopic fractions of $\sim$20%. With VMC mapping, we are able
to measure precise systemic redshifts, provide an estimate of the total
gravitating mass, and maintain high levels of purity and completeness at
$z\sim1$ even with only moderate levels of spectroscopy. Other methods (e.g.,
red-sequence overdensities and hot medium reliant detections) begin to fail at
similar redshifts, which attests to VMC mapping's potential to be a powerful
tool for current and future wide-field galaxy evolution surveys at $z\sim1$ and
beyond.
