Luminosity density of galaxies and cosmic star formation rate from a cold dark matter hydrodynamical simulations

We compute the cosmic star formation rate (SFR) and the rest-frame comoving luminosity density in various passbands as a function of redshift using la rge-scale Lambda CDM hydrodynamical simulations, with the aim of understand ing their behavior as a function of redshift. To calculate the luminosity d ensity of galaxies, we use an updated isochrone synthesis model that takes metallicity variations into account. The computed SFR and the UV luminosity density have a steep rise from z = 0 to 1, a moderate plateau between z = 1-3, and a gradual, decrease beyond z = 3. The raw calculated results are s ignificantly above the observed luminosity density, which can be explained either by dust extinction or the possibly inappropriate input parameters of the simulation. We model the dust extinction by introducing a parameter f; the fraction of the total stellar luminosity (not galaxy population) that is heavily obscured and thus only appears in the far-infrared to submillime ter wavelength range. When we correct our input parameters (baryon mass-den sity and the yield of metals) to the current best estimate and apply dust e xtinction with f = 0.65, the resulting luminosity density fits various obse rvations reasonably well, including the present stellar mass density, the l ocal B-band galaxy luminosity density, and the FIR-to-submillimeter extraga lactic background. Our result is consistent with the picture that similar t o 2/3 of the total stellar emission is heavily obscured by dust and observe d only in the FIR. The rest of the emission is only moderately obscured, wh ich can be observed in the optical to near-IR wavelength range. We also arg ue that the steep falloff of the SFR from z = 1 to 0 is partly due to the s hock-heating of the universe at late times, which produces gas that is too hot to easily condense into star-forming regions.