Metal-Free Gas Supply at the Edge of Reionization: Late-Epoch Population III Star Formation

Abstract

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}.

25 pages, 6 figures, ApJ accepted, added references

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• The First Galaxies: Assembly of Disks and Prospects for Direct Detection
• The oldest and most metal poor stars in the APOSTLE Local Group simulations
• The Effects of Population III X-ray and Radio Backgrounds on the Cosmological 21-cm Signal
• Forming massive seed black holes in high-redshift quasar host progenitors
• Heating the IGM by X-rays from Population III Binaries in High Redshift Galaxies
• Compact Stellar Binary Assembly in the First Nuclear Star Clusters and r-Process Synthesis in the Early Universe
• EPOCHS VII: Discovery of high redshift ($6.5<z<12$) AGN candidates in JWST ERO and PEARLS data
• The formation of massive primordial stars in the presence of moderate UV backgrounds
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• Primordial star clusters at extreme magnification
• A self-consistent semi-analytic model for Population III star formation in minihalos
• Conditions for detecting lensed Population III galaxies in blind surveys with the James Webb Space Telescope, the Roman Space Telescope and Euclid
• Finding the First Cosmic Explosions. IV. 90 - 140 M${}_{\odot }$ Pair-Instability Supernovae
• Boosting Lya and HeII 1640A Line Fluxes from Pop III Galaxies: Stochastic IMF Sampling and Departures from Case-B
• Probing the initial mass function of the first stars with transients
• Detecting Pair-Instability Supernovae at z<5 with the James Webb Space Telescope
• On the probability of the extremely lensed $z$=6.2 Earendel source being a Population~III star
• PopIII signatures in the spectra of PopII/I GRBs
• The high-redshift tail of stellar reionization in LCDM is beyond the reach of the low-$\ell$ CMB
• Radiation magnetohydrodynamics simulations of Population III star formation during the Epoch of Reionization
• Revealing the formation histories of the first stars with the cosmic near-infrared background