1. The Interplay Between First Stars and Metal Enrichment
Japan-Italy meeting Niigata Dec
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

3. 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

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
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

5. 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

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

7. 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

8. 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

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

10. 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

11. Inhomogenous IGM metal enrichment
Chemical feedback
Inhomogenous IGM metal enrichment
The 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

12. 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> > z < 15
PopIII star formation rate
z  10 and
z < 10
Scannapieco, RS & Ferrara (2003)
Japan-Italy meeting Niigata Dec

13. Validation of the model & Observational consequences

14. 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 HE
M = 0.8 Msun
[Fe/H] =-5.3
Christlieb et al (2002)
Japan-Italy meeting Niigata Dec

15. [Fe/H] = -5.3 [C/Fe]= 4.0 [N/Fe] = 2.3
Observational consequences
The origin of HE
Peculiar features:
[Fe/H] = [C/Fe]= [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

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

17. 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

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