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 \sim 1 ) 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 } \ga 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 \sim 1 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 \sim 1 and beyond .