SIMULATIONS OF DEEP GALAXY FIELDS .1. MONTE-CARLO SIMULATIONS OF OPTICAL AND NEAR-INFRARED COUNTS

Monte Carlo simulations of three-dimensional galaxy distributions are performed, following the 1988 prescription of Chokshi & Wright, to stu dy the photometric properties of evolving galaxy populations in the op tical and near-infrared bands to high redshifts. Galaxies are spatiall y distributed according to the spatial two-point correlation function in a range of cluster to field environments and in volume elements app ropriate to the cosmological model under consideration. Details of ind ividual galaxy properties, including luminosities, morphologies, disk- to-bulge ratios, and size distributions are simulated to match local o bserved galaxy properties. Galaxies have evolving gas fraction, metall icity, and spectral energy distributions that include both stellar emi ssion and internal dust absorption and reemission. The simulations res ult in noiseless two-dimensional galaxy distributions on the sky that can be compared to the observed deep images in the blue and near-infra red bands. In this paper, the first of a series, we present our baseli ne model in which galaxy numbers are conserved, and in which no explic it ''starburst'' population is included. We use the model in an attemp t to simultaneously fit published blue and near-infrared photometric a nd spectroscopic observations of deep fields. We find that our baselin e models, with a formation redshift, z(f), of 1000, and H-0 = 50, are able to reproduce the observed blue counts to b(j) = 22, independent o f the value of OMEGA0, and also to provide a satisfactory fit to the o bserved blue-band redshift distributions, but for no value of OMEGA0 d o we achieve an acceptable fit to the fainter blue counts. In the K ba nd, we fit the number counts to the limit of the present-day surveys o nly for an OMEGA0 = 0 cosmology. We investigate the effect on the mode l fits of varying the cosmological parameters H-0, the formation redsh ift z(f), and the local luminosity function. Changing H-0 does not imp rove the fits to the observations. However, reducing the epoch of gala xy formation used in our simulations has a substantial effect. In part icular, a model with z(f) congruent-to 5 in a low OMEGA0 universe impr oves the fit to the faintest photometric blue data without any need to invoke a new population of galaxies, substantial merging, or a signif icant starburst galaxy population. For an OMEGA0 = 1 universe, however , reducing z(f) is less successful at fitting the blue-band counts and has little effect at all at K. Varying the parameters of the local lu minosity function can also have a significant effect. In particular th e steep low end slope of the local luminosity function of Franceschini et al. allows an acceptable fit to the b(j) less-than-or-equal-to 25 counts for OMEGA0 = 1, but is incompatible with OMEGA0 = 0.