The Interplay Between First Stars and Metal Enrichment 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

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

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

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 Both these properties favor the formation of stars with large masses  a few hundred solar masses, as also confirmed by different full 3D numerical simulations. Recently, we have developed a one-zone semi-analytic model to follow the thermodynamics of the collapsing gas in the regime unaccessible to numerical simulations: indeed we find that the fragmentation properties of the gas are very different depending on the initial metallicity of the gas, ie on the inital fraction of gas in metals. In particular, we find that there exist a critical value of the metallicity which marks a trnsition from a high-mass fragmetation mode to a low mass frgamentation mode, more similar to the one presently observed in evolved systems around us. Smaller fragment masses Higher gas opacity RS, Ferrara, Natarajan, Omukai (2002) Japan-Italy meeting Niigata Dec 2-6 2003

Critical O and C abundances Critical metallicity Critical O and C abundances Main gas coolants after H2: CI, CII and OI atomic fine structure transitions CO molecular rovibrational transitions Zcr = 10-51 Zsun 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 [O/H]cr=-3.05  0.2 [C/H]cr=-3.5  0.1 Bromm & Loeb 2003 Extra cooling agent DUST GRAINS Japan-Italy meeting Niigata Dec 2-6 2003

Dust-induced fragmentation 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

Dust formation in PISN ejecta Critical metallicity Dust formation in PISN ejecta 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

Critical metallicity Mdust/Mstar = 20 – 30 % fdep = 40 – 60 % 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

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

Transition is driven by metal enrichment from the first PISN Critical metallicity The emerging scenario Pop III Stars Last Scattering Surface Pop II/I Stars PISN <Z> < Zcr <Z> > Zcr SNII 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

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

PopII & PopIII star formation histories 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 PopIII Stars PopII Stars Mean IGM Metallicity <Z> > Zcr @ z < 15 PopIII star formation rate peaks @ z  10 and continues @ z < 10 Scannapieco, RS & Ferrara (2003) Japan-Italy meeting Niigata Dec 2-6 2003

Validation of the model & Observational consequences

Extremely metal-poor halo stars as living fossils 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 HE0107-5240 M = 0.8 Msun [Fe/H] =-5.3 Christlieb et al (2002) Japan-Italy meeting Niigata Dec 2-6 2003

[Fe/H] = -5.3 [C/Fe]= 4.0 [N/Fe] = 2.3 Observational consequences 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 Are there the conditions for low-mass star formation in the metal enriched gas cloud ? Zcloud  Zcr Japan-Italy meeting Niigata Dec 2-6 2003

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

PopIII footprints in the intracluster medium (ICM) 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 PopIII Stars & Broad Line Regions of high-redshift QSOs Venkatesan, Schneider & Ferrara (2003) 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 Finally, we have combined the PopIII distribution with the predicted energetic & metal yieds of pair-creation SN to study their impact on the intracluster medium. Indeed, large galaxy clusters are predicted tp form in the rare high density peaks in the primordial power spectrum, corresponding to the gravitational collapse of regions of several Mpc. These systems are cosidered to be “closed boxes”, isolated systems that reflect the overall history of the structure formation with negligible interaction with the surroundings. For this reason, they should mantain clear imprints of thermal and chemical evolution of the baryons and it is therefore an ideal place to look for signatures of the first stars: especially now that Chandra and XMM are providing an enormous amount of data on their complex internal structure. For instance the observed X-ray properties of clusters provide a strong contraint on the thermal hisotry of the ICM. Indeed, it is well known that the shape of the X-ray luminosity-temperature relation hints a more complicated thermal hisotry than that coming from pure gravitational heating: at low temperatures, clusters of widely different luminosities have all temperatures of order 1 keV. The accepted explnation is the presence of a large scale energy input from astrophysical sources prior to gravitational collapse of the cluster. Can we think of PopIII stars as contributing to this extra-energy input? Here we show the fraction of Cluster gas mass that has been prcessed thorugh PopIII objects as a function of chemical feedback. Solid and dashed lines refer to 2 different ways of accounting for multiple outflows (feedback) and within each set of curves each plot referes to cluster formation redshift varying between 2 and 0.5 (fro top to bottom). It is possible to see that even in the most optimistic case, no more than 10% of the gas mass is processed through PopIII objects. In the bottom panel we show the degree of cluster gas pre-heating that PopIII stars can contribute. In dense environments: Chemical feedback is strong Prompt transition from PopIII  PopII Japan-Italy meeting Niigata Dec 2-6 2003

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