The Interplay Between First Stars and Metal Enrichment

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