  As energetic particles diffuse out of radio and star-forming galaxies (SFGs),
their intracluster density builds up to a level that could account for a
substantial part or all the emission from a radio halo. We calculate the
particle time-dependent, spectro-spatial distributions from a solution of a
diffusion equation with radio galaxies as sources of electrons, and SFGs as
sources of both electrons and protons. Whereas strong radio galaxies are
typically found in the cluster (e.g., Coma) core, the fraction of SFGs
increases with distance from the cluster center. Scaling particle escape rates
from their sources to the reasonably well determined Galactic rates, and for
realistic gas density and magnetic field spatial profiles, we find that
predicted spectra and spatial profiles of radio emission from primary and
secondary electrons are roughly consistent with those deduced from current
measurements of the Coma halo (after subtraction of emission from the relic
Coma A). Nonthermal X-ray emission is predicted to be mostly by Compton
scattering of electrons from radio galaxies off the CMB, whereas $\gamma$-ray
emission is primarily from the decay of neutral pions produced in interactions
of protons from SFGs with protons in intracluster gas.
