DETECTIFz galaxy groups in the REFINE survey -- 1. Group detection and
  quenched fraction evolution at $z < 2.5$
  We use a large K-selected sample of 299,961 galaxies from the REFINE survey,
consisting of a combination of data from three of the deepest near-infrared
surveys: UKIDSS UDS, COSMOS/UltraVISTA and CFHTLS-D1/VIDEO, that were
homogeneously reduced to obtain photometric redshifts and stellar masses. We
detect 2588 candidate galaxy groups up to $z=3.15$ at $S/N>1.5$. We build a
very pure ($>90\%$) sample of 448 candidate groups up to $z=2.5$ and study some
of their properties. Cluster detection is done using the DElaunay TEssellation
ClusTer IdentiFication with photo-z (DETECTIFz) algorithm that we describe.
This new group finder algorithm uses the joint probability distribution
functions (PDF) of redshift and stellar-mass of galaxies to detect groups as
stellar-mass overdensities in overlapping redshift slices, where density is
traced using Monte Carlo realisation of the Delaunay Tessellation Field
Estimator (DTFE). We compute the algorithm selection function using mock galaxy
catalogues taken from cosmological N-body simulation lightcones. Based on these
simulations, we reach a completeness of $\sim80\%$ for clusters
($M_{200}>10^{14} M_{\odot}$) at a purity of $\sim90\%$ at $z<2.5$. Using our
403 most massive candidate groups, we constrain the redshift evolution of the
group galaxy quenched fraction at $0.12\le z<2.32$, for galaxies with $10.25 <
\log M_\star/M_{\odot} < 11$ in $0.5\times R_{200}$. We find that the quenched
fraction in group cores is higher than in the field in the full redshift range
considered, the difference growing with decreasing redshift. This indicates
either more efficient quenching mechanisms in group cores at lower redshift or
pre-processing by cosmic filaments.
