Glimpsing the imprint of local environment on the galaxy stellar mass function

Abstract

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 M . 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).

Establishing a new technique for discovering large-scale structure using the ORELSE survey

“…These targets were the highest priority (priority 1), and we assigned progressively lower priority to progressively bluer objects. Though our selection scheme heavily favored redder objects, the majority of our spectroscopic targets had colors bluer than the highest priority objects, due to the relative rarity of objects at these red colors and the strictness of our cuts, as discussed in depth in Tomczak et al (2017). The fraction of priority 1 targets in our final sample ranged from ∼1% to ∼45% across all ORELSE fields.…”

“…The optical CFHTLS observations were reduced and photometrically calibrated using TERAPIX routines following the methods described in Ilbert et al (2006) and the T0006 CFHTLS handbook 4 . For further details on the reduction of these data, see Tomczak et al (2017). Near-infrared (NIR) J and K/K s imaging was taken for every ORELSE field but Cl1350.…”

“…These data were provided by the Spitzer Heritage Archive in the form of basic calibrated data (cBCD) images and were reduced using the MOsaicker and Point source EXtractor (MOPEX; Makovoz & Marleau 2005) package and several custom Interactive Data Language (IDL) scripts written by J. Surace. Further details on these data reduction can be found in Tomczak et al (2017).…”

“…For each field, all optical and non-Spitzer images were registered to a common grid of plate scale 0.2 pixel −1 and then convolved to the field's worst point spread function (PSF) using the methods described in Tomczak et al (2017). The worst PSF for each field was between ∼1.00 -1.96 , with Cl1350 being the only field with an image that had a PSF greater than 1.4 .…”

“…We generate the mocks by first populating a given volume with a population of field galaxies and then injecting galaxy clusters and groups. To simplify the distribution of the field galaxies in our mocks, we drew them from ORELSE fields where we did not find any structure candidates at the redshift of interest and also had deep enough imaging in the relevant bands such that it included a complete sample of galaxies to the magnitude limit given below (see Tomczak et al 2017 for more details on the completeness limits of our imaging).…”