How to Identify and Separate Bright Galaxy Clusters from the
  Low-frequency Radio Sky?
  In this work we simulate the $50-200$ MHz radio sky that is constrained in
the field of view ($5^{\circ}$ radius) of the 21 Centimeter Array (21CMA), by
carrying out Monte-Carlo simulations to model redshifted cosmological
reionization signals and strong contaminating foregrounds, including emissions
from our Galaxy, galaxy clusters, and extragalactic point sources. As an
improvement of previous works, we consider in detail not only random variations
of morphological and spectroscopic parameters within the ranges allowed by
multi-band observations, but also evolution of radio halos in galaxy clusters,
assuming that relativistic electrons are re-accelerated in the ICM in merger
events and lose energy via both synchrotron emission and inverse Compton
scattering with CMB photons. By introducing a new approach designed on the
basis of independent component analysis (ICA) and wavelet detection algorithm,
we prove that, with a cumulative observation of one month with the 21CMA array,
about $80\%$ of galaxy clusters with central brightness temperatures of $>
10~{\rm K}$ at 65 MHz can be safely identified and separated from the
overwhelmingly bright foreground. We find that the morphological and
spectroscopic distortions are extremely small as compared to the input
simulated clusters, and the reduced $\chi^2$ of brightness temperature profiles
and spectra are controlled to be $\lesssim 0.5$ and $\lesssim 1.3$,
respectively. These results robustly indicate that in the near future a sample
of dozens of bright galaxy clusters will be disentangled from the foreground in
21CMA observations, the study of which will greatly improve our knowledge about
cluster merger rates, electron acceleration mechanisms in cluster radio halos,
and magnetic field in the ICM.
