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The Interplay Between First Stars and Metal Enrichment

This presentation discusses the critical metallicity, chemical feedback, and cosmic star formation history in the context of first stars and metal enrichment. It covers topics such as metal footprints, extremely metal-poor stars, and the fate of the first stars in the early universe.

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The Interplay Between First Stars and Metal Enrichment

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  1. Japan-Italy meeting Niigata Dec 2-6 2003 The Interplay Between First Stars and Metal Enrichment Raffaella Schneider Arcetri Astrophysical Observatory - Florence Enrico Fermi Center - Rome Andrea Ferrara & Ruben Salvaterra SISSA-Trieste Kazuyuki Omukai NAO-Tokyo

  2. Outline • Introduction • The critical metallicity • “Chemical feedback” & cosmic star formation history • Validation of the model & observational predictions • metal footprints in the ICM and QSO BLRs • extremely metal-poor halo stars • Conclusions Japan-Italy meeting Niigata Dec 2-6 2003

  3. 140 Msun < M < 260 Msun PISN pair-creation supernovae ejection of all metals no remnants BH black hole collapse no metal/mass ejected very massive BH remnants 50 Msun < M <140 Msun M > 260 Msun Heger & Woosley 2002 Introduction PISNenergy/metal input in the IGM RS, Guetta & Ferrara 2002 BH high-redshift GRBs high-energy neutrinos seeds for SMBH formation Umemura’s Talk! The Fate of the first stars Important sources of light Japan-Italy meeting Niigata Dec 2-6 2003

  4. Critical metallicity and IMF transition Primordial environments favor the formation of stars with large masses of a few 100 Msun Transition from high-mass stars to low-mass stars Zcr = 10-51 Zsun • Smaller fragment masses • Higher gas opacity RS, Ferrara, Natarajan, Omukai (2002) Japan-Italy meeting Niigata Dec 2-6 2003

  5. Zcr = 10-51 Zsun Bromm & Loeb 2003 [O/H]cr=-3.05  0.2 [C/H]cr=-3.5  0.1 Critical metallicity Critical O and C abundances • Main gas coolants after H2: • CI, CII and OI atomic fine structure transitions • CO molecular rovibrational transitions Abundances of local interstellar clouds [O/H]cr=-5.381 [C/H]cr=-5.59 1 Abundances of 200 Msun PISN ejecta [O/H]cr=-5.431 [C/H]cr=-5.94 1 Extra cooling agent DUST GRAINS Japan-Italy meeting Niigata Dec 2-6 2003

  6. Critical metallicity Dust-induced fragmentation RS, Ferrara, Salvaterra, Omukai & Bromm Nature 2003 Z=10-5.1 Zsun Low mass stars can form @ Z=Zcr if 20% of metals are depleted onto dust grains Japan-Italy meeting Niigata Dec 2-6 2003

  7. Critical metallicity Dust formation in PISNejecta Apply the model of Todini & Ferrara (2001) to PISN • Larger explosion kinetic energy • Larger ejected mass of metals  Dust depletion factor ? fdep 18% Mdust 8% Mstar Schneider, Ferrara & Salvaterra (2003) Japan-Italy meeting Niigata Dec 2-6 2003

  8. Critical metallicity Nozawa et al (2003) Mdust/Mstar = 20 – 30 % fdep = 40 – 60 % • Large amount of Si and O • in PISN ejecta: • SiO + O  SiO2 • Si + 2O  SiO2 Japan-Italy meeting Niigata Dec 2-6 2003

  9. Critical metallicity General Picture ~ 100 Msun ~ 1 Msun ~ 0.1 Msun Japan-Italy meeting Niigata Dec 2-6 2003

  10. PISN SNII Critical metallicity The emerging scenario Pop III Stars Last Scattering Surface Pop II/I Stars <Z> < Zcr <Z> > Zcr Very massive stars Normal Stars Z= 0 BH Z= 6 Transition redshift zf Z = 30 Z=1000 Transition is driven by metal enrichment from the first PISN Chemical Feedback Japan-Italy meeting Niigata Dec 2-6 2003

  11. The IGM @ z  3 7 h-1 Mpc Z > Zcr Temperature Metallicity Z < Zcr • Chemical feedback is local • Coeval epochs of PopII and PopIII star formation Chemical feedback Inhomogenous IGM metal enrichment Marri et al in prep Cosmic star formation history depends on chemical feedback Japan-Italy meeting Niigata Dec 2-6 2003

  12. PopIII Stars PopII Stars Mean IGM Metallicity <Z> > Zcr @ z < 15 PopIII star formation rate peaks @ z  10 and continues @ z < 10 Observational consequences PopII & PopIII star formation histories Chemical feedback parametrized as Eg = energy per unit gas mass in outflows • efficiency of PopIII star formation f*III • fraction of PISN(PopIII IMF) • efficiency of outflow generation fwIII Scannapieco, RS & Ferrara (2003) Japan-Italy meeting Niigata Dec 2-6 2003

  13. Validation of the model & Observational consequences

  14. Christlieb et al (2002) HE0107-5240 M = 0.8 Msun [Fe/H] =-5.3 Observational consequences Extremely metal-poor halo stars as living fossils • No Z=0 star found  first generation of stars is very massive! • Many stars found with [Fe/H]>-4  small-mass stars only if Z>Zcr Japan-Italy meeting Niigata Dec 2-6 2003

  15. Are there the conditions for low-mass star formation in the metal enriched gas cloud ? Observational consequences Zcloud  Zcr The origin of HE0107-5240 Peculiar features: [Fe/H] = -5.3 [C/Fe]= 4.0 [N/Fe] = 2.3 The star is a member of a second stellar generation • What is the nature of the first (Z=0) stellar generation ? • from observed elemental yields  mass range of Z=0 SN Japan-Italy meeting Niigata Dec 2-6 2003

  16. HE0107-5240 HE0107-5240 B. Post-formation C and N enrichment (RS, Ferrara, Salvaterra, Omukai & Bromm 2003) Zcloud  Zcr Observational consequences A. Pre-formation C and N enrichment(Umeda & Nomoto 2003) Zcloud  Zcr The origin of HE0107-5240 is consistent with Zcr criterium Japan-Italy meeting Niigata Dec 2-6 2003

  17. PopIII Stars & Broad Line Regions of high-redshift QSOs Venkatesan, Schneider & Ferrara (2003) Observational consequences PopIII footprints in the intracluster medium (ICM) Scannapieco, RS, Ferrara (2003) • Max 10% of the Cluster gas mass is processed through PopIII objects • PISN heating is too low to account for the extra-energy required to match Lx-T • Metal yields from PISN help reconcile the observed Fe and Si abundances • PISN can reproduce Fe/Mg data but not C/N data • Stars with a Salpeter IMF can fit data • Type Ia SNe are not required by data • In dense environments: • Chemical feedback is strong • Prompt transition from PopIII  PopII Japan-Italy meeting Niigata Dec 2-6 2003

  18. Conclusions • First Stars are very massive • Transition to “normal” stars regulated by metals and dust • “critical metallicity” • Interplay between PopIII stars and metal enrichment • “chemical feedback” • Chemical feedback is local: coeval PopIII and PopII/I • Increasing number of observational constraints to • improve/test the emerging scenario Japan-Italy meeting Niigata Dec 2-6 2003

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