  We investigate the impact of local environment on the galaxy stellar mass
function (SMF) spanning a wide range of galaxy densities from the field up to
dense cores of massive galaxy clusters. Data are drawn from a sample of eight
fields from the Observations of Redshift Evolution in Large-Scale Environments
(ORELSE) survey. Deep photometry allow us to select mass-complete samples of
galaxies down to 10^9 Msol. Taking advantage of >4000 secure spectroscopic
redshifts from ORELSE and precise photometric redshifts, we construct
3-dimensional density maps between 0.55<z<1.3 using a Voronoi tessellation
approach. We find that the shape of the SMF depends strongly on local
environment exhibited by a smooth, continual increase in the relative numbers
of high- to low-mass galaxies towards denser environments. A straightforward
implication is that local environment proportionally increases the efficiency
of (a) destroying lower-mass galaxies and/or (b) growth of higher-mass
galaxies. We also find a presence of this environmental dependence in the SMFs
of star-forming and quiescent galaxies, although not quite as strongly for the
quiescent subsample. To characterize the connection between the SMF of field
galaxies and that of denser environments we devise a simple semi-empirical
model. The model begins with a sample of ~10^6 galaxies at z_start=5 with
stellar masses distributed according to the field. Simulated galaxies then
evolve down to z_final=0.8 following empirical prescriptions for
star-formation, quenching, and galaxy-galaxy merging. We run the simulation
multiple times, testing a variety of scenarios with differing overall amounts
of merging. Our model suggests that a large number of mergers are required to
reproduce the SMF in dense environments. Additionally, a large majority of
these mergers would have to occur in intermediate density environments (e.g.
galaxy groups).
