The Persistence of Population III Star Formation

We present a semi-analytic model of star formation in minihaloes below the atomic cooling threshold in the early Universe, beginning with the first metal-free stars. By employing a completely feedback-limited star formation prescription, stars form until the self-consistently calculated feedback processes halt formation. We account for a number of feedback processes including a metagalactic Lyman-Werner (LW) background, supernovae, photoionization, and chemical feedback. Haloes are evolved combining mass accretion rates found through abundance matching with our feedback-limited star formation prescription, allowing for a variety of Population III (Pop III) initial mass functions (IMFs). We find that, for a number of models, minihalo Pop III star formation can continue on until at least z similar to 20 and potentially past z similar to 6 at rates of around 10(-4) to 10(-5) M-circle dot yr(-1) Mpc(-3), assuming these stars form in isolation. At this point LW feedback pushes the minimum halo mass for star formation above the atomic cooling threshold, where we assume that the mode of star formation changes. We find that, in most models, Pop II and Pop III star formation coexist over cosmological time-scales, with the total star formation rate density and resulting radiation background strongly dominated by the former before Pop III star formation finally ends. These molecular cooling haloes form at most similar to 10(3)M(circle dot) of minihalo Pop III stars over multiple generations during this phase and typically have absolute magnitudes in the range of M-AB = -5 to -10. We also briefly discuss how future observations from telescopes such as James Webb Space Telescope or Wide-Field Infrared Survey Telescope and 21-cm experiments may be able to constrain unknown parameters in our model such as the IMF, star formation prescription, or the physics of Pop III stars in minihaloes.