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The 21-cm signal in the vicinity of the first stars is expected to reflectproperties of the first stars. In this study we pay special attention totracing the time evolution of the ionizing photons' escape fraction, whichaffects the distribution of neutral hydrogen, by performing radiationhydrodynamics (RHD) simulations resolving dense gas in a halo. We find that theradial profile of 21-cm differential brightness temperature is quite sensitiveto the stellar and halo masses, which reflects the time evolution of the escapefraction. In the case of a less massive star, ionizing photons hardly escapefrom its host halo due to the absorption by dense halo gas, thus an deep 21-cmabsorption feature at just outside the halo lasts a long time. Whereas photonsfrom a massive star well working to heat the ambient intergalactic medium turnout to cause a spatially extended 21-cm emission signature. Although individualsignals are found to be undetectable with the Square Kilometre Array, ouranalysis using the results from the RHD simulations indicates that theproperties of the first stars are imprinted on the 21-cm global signal: itsamplitude depends not only on the cosmic star formation rate density, but alsoon the typical mass of the first stars due to the stellar-mass-dependentheating rate. Thus, we suggest that the initial mass function of the firststars is an essential factor in understanding the global signal.

Stellar mass dependence of the 21-cm signal around the first star and its impact on the global signal