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Register a new userConfined Population III Enrichment and the Prospects for Prompt Second-Generation Star Formation
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It is widely recognized that nucleosynthetic output of the first, Population III supernovae was a catalyst defining the character of subsequent stellar generations. Most of the work on the earliest enrichment was carried out assuming that the first stars were extremely massive and that the associated supernovae were unusually energetic, enough to completely unbind the baryons in the host cosmic minihalo and disperse the synthesized metals into the intergalactic medium. Recent work, however, suggests that the first stars may in fact have been somewhat less massive, with a characteristic mass scale of a few tens of solar masses. We present a cosmological simulation following the transport of the metals synthesized in a Population III supernova assuming that it had an energy of 1e51 ergs, compatible with standard Type II supernovae. A young supernova remnant is inserted in the first stars relic HII region in the free expansion phase and is followed for 40 Myr employing adaptive mesh refinement and Lagrangian tracer particle techniques. The supernova remnant remains partially trapped within the minihalo and the thin snowplow shell develops pronounced instability and fingering. Roughly half of the ejecta turn around and fall back toward the center of the halo, with 1% of the ejecta reaching the center in 30 kyr and 10% in 10 Myr. The average metallicity of the combined returning ejecta and the pristine filaments feeding into the halo center from the cosmic web is 0.001 - 0.01 Z_sun, but the two remain unmixed until accreting onto the central hydrostatic core that is unresolved at the end of the simulation. We conclude that if Population III stars had less extreme masses, they promptly enriched the host minihalos with metals and triggered Population II star formation.
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We use cosmological simulations to assess how the explosion of the first stars in supernovae (SNe) influences early cosmic history. Specifically, we investigate the impact by SNe on the host systems for Population~III (Pop~III) star formation and explore its dependence on halo environment and Pop~III progenitor mass. We then trace the evolution of the enriched gas until conditions are met to trigger second-generation star formation. To this extent, we quantify the recovery timescale, which measures the time delay between a Pop~III SN explosion and the appearance of cold, dense gas, out of which second-generation stars can form. We find that this timescale is highly sensitive to the Pop~III progenitor mass, and less so to the halo environment. For more massive progenitors, including those exploding in pair instability SNe, second-generation star formation is delayed significantly, for up to a Hubble time. The dependence of the recovery time on the mass of the SN progenitor is mainly due to the ionizing impact of the progenitor star. Photoionization heating increases the gas pressure and initiates a hydrodynamical response that reduces the central gas density, an effect that is stronger in more massive. The gas around lower mass Pop~III stars remains denser and hence the SN remnants cool more rapidly, facilitating the subsequent re-condensation of the gas and formation of a second generation of stars. In most cases, the second-generation stars are already metal-enriched to ~2-5 X 10^{-4}zsun, thus belonging to Population~II. The recovery timescale is a key quantity governing the nature of the first galaxies, able to host low-mass, long-lived stellar systems. These in turn are the target of future deep-field campaigns with the James Webb Space Telescope.
We investigate the formation of extremely metal-poor (EMP) stars that are observed in the Galactic halo and neighboring ultra-faint dwarf galaxies. Their low metal abundances (${rm [Fe/H]} < -3$) indicate that their parent clouds were enriched by a single or several supernovae (SNe) from the first (Pop III) stars. In this study, we perform numerical simulations of the entire formation sequence of a EMP star through the feedback effects of photo-ionization and metal-enrichment by a Pop III SN. We for the first time employ a metal/dust properties calculated consistently with the progenitor model, and solve all relevant radiative cooling processes and chemical reactions including metal molecular formation and grain growth until the protostar formation. In a minihalo (MH) with mass $1.77times 10^{6} {rm M}_{bigodot}$, a Pop III star with mass $13 {rm M}_{bigodot}$ forms at redshift $z=12.1$. After its SN explosion, the shocked gas falls back into the central MH internally enriching itself. The metallicity in the recollapsing region is $2.6times 10^{-4} {rm Z}_{bigodot}$ (${rm [Fe/H]} = -3.42$). The recollapsing cloud undergoes cooling by HD, CO, and OH molecules and heating along with H$_2$ formation. Eventually by grain growth and dust cooling, knotty filaments appear in the central 100 au region with the help of turbulence driven by the SN, leading to the formation of low-mass EMP stars surviving until the present day.
Population III star formation during the dark ages shifted from minihalos (~10^6 Msun) cooled via molecular hydrogen to more massive halos (~10^8 Msun) cooled via Ly-alpha as Lyman-Werner backgrounds progressively quenched molecular hydrogen cooling. Eventually, both modes of primordial star formation were suppressed by the chemical enrichment of the IGM. We present a comprehensive model for following the modes of Population III star formation that is based on a combination of analytical calculations and cosmological simulations. We characterize the properties of the transition from metal-free star formation to the first Population II clusters for an average region of the Universe and for the progenitors of the Milky Way. Finally, we highlight the possibility of observing the explosion of Population III stars within Ly-alpha cooled halos at redshift z~6 in future deep all sky surveys such as LSST.
While the average metallicity of the intergalactic medium rises above Z~10^{-3} Zsun by the end of the reionization, pockets of metal-free gas can still exist at later times. We quantify the presence of a long tail in the formation rate of metal-free halos during late stages of reionization (redshift z~6), which might offer the best window to detect Population III stars. Using cosmological simulations for the growth of dark matter halos, coupled with analytical recipes for the metal enrichment of their interstellar medium, we show that pockets of metal-free gas exist at z~6 even under the assumption of high efficiency in metal pollution via winds. A comoving metal-free halo formation rate d^2n/dtdV > 10^{-9} Mpc^{-3}yr^{-1} is expected at z=6 for halos with virial temperature T_{vir}~10^4 K (mass ~10^8 Msun), sufficient to initiate cooling even with strong negative radiative feedback. Under the assumption of a single Population III supernova formed per metal-free halo, we expect an observed supernova rate of 2.6x10^{-3} deg^{-2}yr^{-1} in the same redshift range. These metal-free stars and their supernovae will be isolated and outside galaxies (at distances >150 h^{-1} kpc) and thus significantly less biased than the general population of ~10^8 Msun halos at z~6. Supernova searches for metal-free explosions must thus rely on large area surveys. If metal-free stars produce very luminous supernovae, like SN2006gy, then a multi-epoch survey reaching m_AB =27 at 1 micron is sufficient for detecting them at z=6. While the Large Synoptic Survey Telescope will not reach this depth in the z band, it will be able to detect several tens of Population III supernovae in the i and r bands at z <5.5, when their observed rate is down to 3-8x10^{-4} deg^{-2} yr^{-1}.
We investigate the effect of the population III (Pop III) stars supernova explosion~(SN) on the high redshifts reionization history using the latest Planck data. It is predicted that massive Pop~III stars~($130M_odotleq Mleq 270M_odot$) explode energetically at the end of their stellar life as pair-instability supernovae (PISNe). In the explosion, supernova remnants grow as hot ionized bubbles and enhance the ionization fraction in the early stage of the reionization history. This enhancement affects the optical depth of the cosmic microwave background~(CMB) and generates the additional anisotropy of the CMB polarization on large scales. Therefore, analyzing the Planck polarization data allows us to examine the Pop III star SNe and the abundance of their progenitors, massive Pop III stars. In order to model the SN contribution to reionization, we introduce a new parameter $zeta$, which relates to the abundance of the SNe to the collapse fraction of the Universe. Using the Markov chain Monte Carlo method with the latest Planck polarization data, we obtain the constraint on our model parameter, $zeta$. Our constraint tells us that observed CMB polarization is consistent with the abundance of PISNe predicted from the star formation rate and initial mass function of Pop III stars in recent cosmological simulations. We also suggest that combining further observations on the late reionization history such as high redshift quasi-stellar object~(QSO) observations can provide tighter constraints and important information on the nature of Pop III stars.
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