We use a model developed by Xu,Ferrara,and Chen(Mon Not Roy Astron Soc,submitted) to compute the 21 cm line absorption signatures imprinted by star-forming dwarf galaxies(DGs) and starless minihalos(MHs). The method,based on a statistical comparison of the equivalent width(W ν ) distribution and flux correlation function,allows us to derive a simple selection criteria for candidate DGs at very high(z ≤ 8) redshift. We find that ≈18% of the total number of DGs along a line of sight to a target radio source(GRB or quasar) can be identified by the condition W ν<0; these objects correspond to the high-mass tail of the DG distribution at high redshift,and are embedded in large HII regions. The criterion W ν>0.37 kHz instead selects ≈11% of MHs. Selected candidate DGs could later be re-observed in the near-IR by the JWST with high efficiency,thus providing a direct probe of the most likely reionization sources.
