High-redshift evolution of optical- and infrared-selected galaxies: a comparison with cold dark matter scenarios

A combination of ground-based (NTT and VLT) and Hubble Space Telescope (HST ) (HDF-N and HDF-S) public imaging surveys has been used to collect a sampl e of 1712 I-selected and 319 K less than or equal to 21 galaxies observed w ith an extended spectral coverage from U to K bands. Photometric redshifts have been obtained for all these galaxies, using a spectral library compute d from Bruzual & Charlot models. The results have been compared with the pr ediction of an analytic rendition of the current cold dark matter (CDM) hie rarchical models for galaxy formation that explicitly accounts for magnitud e limits and dust extinction. We focus in particular on two observed quanti ties: the galaxy redshift distribution at K less than or equal to 21 and th e evolution of the UV luminosity density. The former has been proposed by K auffmann & Charlot to be a very robust prediction of any CDM hierarchical m odel, and we show that it is remarkably constant among different cosmologic al models. The derived photometric redshift distribution is in agreement wi th the hierarchical CDM prediction, with a fraction of only 5 per cent of g alaxies detected at z greater than or equal to 2. This result strongly supp orts hierarchical scenarios where present-day massive galaxies are the resu lt of merging processes. The observed UV luminosity density in our I-select ed sample is confined within a factor of 4 over the whole range 0 < z < 4.5 , in agreement with previous spectroscopic and photometric surveys. CDM mod els in a critical (Omega = 1, Lambda = 0) Universe are not able to produce the density of UV photons that is observed at z greater than or equal to 3. CDM models in a Lambda-dominated universe are in better agreement at 3 les s than or equal to z less than or equal to 4.5, but predict a pronounced pe ak at z similar or equal to 1.5 and a drop by a factor of 8 from z = 1.5 to z = 4 that is not observed in the data. We conclude that improvements are required in the treatment of the physical processes directly related to the star formation rate (SFR), e.g. the starburst activity in merger processes and/or different recipes for linking the supernova feedback to the star fo rmation activity.