We present a new evolutionary model for predicting the far-UV to sub-mm properties of the galaxy population .
This combines a semi-analytic galaxy formation model based on hierarchical clustering ( GALFORM , 19 ) with a spectro-photometric code which includes dust reprocessing ( GRASIL , 80 ) .
The former provides the star formation and metal enrichment histories , together with the gas mass and various geometrical parameters , for a representative sample of galaxies formed in different density environments .
These quantities , together with a few other assumptions concerning the spatial distribution of dust and its optical properties , allow us to model the spectral energy distributions ( SEDs ) of galaxies , taking into account stellar emission and also dust extinction ( absorption plus scattering ) and re-emission .
In the spectro-photometric code dust is considered only in the disk , but the general radiation field is contributed by both the disk and the bulge components with their own distinct age and metallicity distributions .
Two phases are considered for the dust : molecular cloud complexes , where stars are assumed to be born , and the diffuse interstellar medium .
The model includes both galaxies forming stars quiescently in disks , and starbursts triggered by galaxy mergers .
We test our models against the observed spectro-photometric properties of galaxies in the local Universe , assuming a CDM cosmology with \Omega _ { 0 } = 0.3 and \Lambda _ { 0 } = 0.7 .
The models reproduce fairly well the SEDs of normal spirals and starbursts from the far-UV to the sub-mm , and their internal extinction properties .
The starbursts follow the observed relationship between the FIR to UV luminosity ratio and the slope of the UV continuum .
They also reproduce the observed starburst attenuation law ( 16 ) .
This result is remarkable , because we use a dust mixture which reproduces the Milky Way extinction law .
It suggests that the observed attenuation law is closely related to the geometry of the stars and dust .
We compute galaxy luminosity functions over a wide range of wavelengths , which turn out to be in good agreement with observational data in the UV ( 2000Å ) , in the B and K bands , and in the IR ( 12 - 100 \micron ) .
Finally , we investigate the reliability of some star formation indicators which are based on the properties of the continuum SEDs of galaxies .
The UV continuum turns out to be a poor star formation indicator for our models , whilst the infrared luminosity is much more reliable .