We present a first estimate based on a cosmological gasdynamics simulation of
galaxy cluster radio halo counts to be expected in forthcoming low-frequency
radio surveys. Our estimate is based on a FLASH simulation of the LCDM model
for which we have assigned radio power to clusters via a model that relates
radio emissivity to cluster magnetic field strength, intracluster turbulence,
and density. We vary several free parameters of this model and find that radio
halo number counts vary by up to a factor of two for average magnetic fields
ranging from 0.2 to 3.1 uG. However, we predict significantly fewer
low-frequency radio halos than expected from previous semi-analytic estimates,
although this discrepancy could be explained by frequency-dependent radio halo
probabilities as predicted in reacceleration models. We find that upcoming
surveys will have difficulty in distinguishing models because of large
uncertainties and low number counts. Additionally, according to our modeling we
find that expected number counts can be degenerate with both reacceleration and
hadronic secondary models of cosmic ray generation. We find that relations
between radio power and mass and X-ray luminosity may be used to distinguish
models, and by building mock radio sky maps we demonstrate that surveys such as
LOFAR may have sufficient resolution and sensitivity to break this model
degeneracy by imaging many individual clusters.Comment: 18 pages, 14 figures, revised from referee comments, ApJ accepted,
public catalog available at
http://sipapu.astro.illinois.edu/http://sipapu.astro.illinois.edu/foswiki/bin/view/Main/RadioHaloMap
