The Photometric Redshift Distribution and Evolutionary Properties of Galaxies up to z= 4.5 in the Field of the Quasar BR1202-0725

We present a deep BVrIK multicolor catalog of galaxies in the field of the high redshift (z=4.7) quasar BR 1202-0725. Reliable colors have been measured for galaxies selected down to R=25. The choice of the optical filters has been optimized to define a robust multicolor selection of galaxies at 3.8<z< 4.5. Within this interval the surface density of galaxy candidates with z~4 in this field is 1 arcmin^{-2}. Photometric redshifts have been derived for the galaxies in the field with the maximum likelihood analysis using the GISSEL library of ~10^6 synthetic spectra. The accuracy of the method used has been discussed and tested using galaxies in the Hubble Deep Field (HDF) with known spectroscopic redshifts and accurate photometry. A peak in the redshift distribution is present at z~0.6 with relatively few galaxies at z>1.5. At variance with brighter surveys (I<22.5) there is a tail in the distribution towards high redshifts up to z~4. The luminosity function at z~0.6 shows a steepening for M_B>-19. The observed cosmological ultraviolet luminosity density is computed in the overall redshift interval z=0.3-4.5 reaching a value 2x10^{19} W/Hz/Mpc^3 at z~0.8. We have derived in a homogeneous way, using the GISSEL libraries, the physical parameters connected with the fitted spectral energy distributions. The bulk of the blue intermediate redshift population with z=0.4-1 mostly consists of very young star-forming galaxies with a median starburst age of the order of a few 10^8 yr and typical mass in luminous stars ~2x10^8 Mo.