Secondary Star Formation in a Population III Object

Abstract

We explore the possibility of subsequent star formation after a first star forms in a Population III object, by focusing on the radiation-hydrodynamic (RHD) feedback caused by ionizing photons, as well as H2-dissociating photons. For this purpose, we perform three-dimensional RHD simulations in which the radiative transfer of ionizing photons and H2-dissociating photons from a first star is self-consistently coupled with hydrodynamics based on a smoothed particle hydrodynamics method. It is shown that density peaks above a threshold density can keep collapsing, owing to the shielding of H2-dissociating radiation by an H2 shell formed ahead of a D-type ionization front. But, below the threshold density an M-type ionization front with a shock propagates, and density peaks are radiation-hydrodynamically evaporated by the shock. The threshold density depends on the distance from the source star and is ≈102 cm-3 for a source distance of 30 pc. Taking into consideration that the extent of a Population III object is ≈100 pc and the density peaks within it have densities of 102-104 cm-3, it is concluded that secondary star formation is possible in the broad regions of a Population III object.