Early Cosmological Hii/HeiiiRegions and Their Impact on Second‐Generation Star Formation

(Abridged) We present the results of three-dimensionalradiation-hydrodynamics simulations of the formation and evolution of earlyHII/HeIII regions around the first stars. Cooling (by H2 and HD) and recollapseof the gas in the relic HII region is also followed in a full cosmologicalcontext, until second-generation stars are formed. A large HII region with afew kiloparsec diameter is formed, within which a smaller HeIII region isembedded. Radiative feedback effect quenches further star-formation within thehalo for a hundred million years. Accretion onto remnant blackholes will beinefficient. Recombination radiation within the HII region is weak, butpersists for 50 million years. We also follow the thermal and chemicalevolution of the photo-ionized gas in the relic HII region. The gas cools by HDline cooling down to a few tens Kelvin. At high redshifts (z>10), the minimumgas temperature is limited by T_CMB. Because of its low temperature, thecharacteristic mass of a Jeans-unstable gas clump is ~ 40 Msun, and issignificantly smaller than a typical clump mass for early primordial gasclouds. We find no evidence of fragmentation by this epoch. Together with thesmall cloud mass, this result indicates that massive, rather than very massive,primordial stars may form in the relic HII region. Such stars might beresponsible for early metal-enrichment of the interstellar medium from whichrecently discovered hyper metal-poor stars were born.Comment: Version accepted by ApJ. Figures 10, 12, 13 updated using two additional simulation