The Interplay Between
First Stars and Metal
Enrichment
Japan-Italy meeting Niigata Dec 2-6 2003
Raffaella SchneiderArcetri Astrophysical Observatory - Florence
Enrico Fermi Center - Rome
Andrea Ferrara & Ruben Salvaterra SISSA-TriesteKazuyuki Omukai NAO-Tokyo
Outline
o Introduction
o The critical metallicity
o “Chemical feedback” & cosmic star formation history
o Validation of the model & observational predictions
• metal footprints in the ICM and QSO BLRs• extremely metal-poor halo stars
o Conclusions
Japan-Italy meeting Niigata Dec 2-6 2003
The Fate of the first stars
Heger & Woosley 2002
PISN energy/metal input in the IGM
BH high-redshift GRBs high-energy neutrinos seeds for SMBH formation
Important sources of light
PISNpair-creation supernovaeejection of all metals
no remnants
140 Msun < M < 260 Msun
BH black hole collapseno metal/mass ejected
very massive BH remnants50 Msun < M <140 Msun M > 260 Msun
Introduction
Japan-Italy meeting Niigata Dec 2-6 2003
RS, Guetta & Ferrara 2002
Umemura’s Talk!
Critical metallicity and IMF transition
Primordial environments favor the formation of stars with large masses of a few 100 Msun
RS, Ferrara, Natarajan, Omukai (2002)
Transition from high-mass starsto low-mass stars
Zcr = 10-51 Zsun
o Smaller fragment masses
o Higher gas opacity
Japan-Italy meeting Niigata Dec 2-6 2003
Critical O and C abundancesCritical metallicity
Japan-Italy meeting Niigata Dec 2-6 2003
Main gas coolants after H2:
1. CI, CII and OI atomic fine structure transitions
2. CO molecular rovibrational transitions
Zcr = 10-51 Zsun
Abundances of local interstellar clouds[O/H]cr=-5.381 [C/H]cr=-5.59 1
Abundances of 200 Msun PISN ejecta
[O/H]cr=-5.431 [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
Dust-induced fragmentation
Low mass stars can form @ Z=Zcr if 20% of metals are depleted onto dust grains
RS, Ferrara, Salvaterra, Omukai & Bromm Nature 2003
Critical metallicity
Japan-Italy meeting Niigata Dec 2-6 2003
Z=10-5.1 Zsun
Dust formation in PISN ejectaApply the model of Todini & Ferrara (2001) to PISN
o Larger explosion kinetic energyo Larger ejected mass of metals Dust depletion factor ?
fdep 18%
Mdust 8% Mstar
Japan-Italy meeting Niigata Dec 2-6 2003
Critical metallicity
Schneider, Ferrara & Salvaterra (2003)
Japan-Italy meeting Niigata Dec 2-6 2003
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
General Picture
Japan-Italy meeting Niigata Dec 2-6 2003
Critical metallicity
~ 100 Msun
~ 1 Msun
~ 0.1 Msun
The emerging scenario
Last Scattering Surface
Pop III Stars
PISN
<Z> < Zcr
Very massivestars
BH
Normal StarsSNII
Pop II/I Stars
Z=1000
Z= 0
Z = 30
Z= 6
Transition redshift zf
<Z> > Zcr
Transition is driven by metal enrichment from the first PISN
Chemical FeedbackJapan-Italy meeting Niigata Dec 2-6 2003
Critical metallicity
Inhomogenous IGM metal enrichment The IGM @ z 3
Temperature Metallicity
7 h
-1 M
pc Z > Zcr
Z < Zcr
Marri et al in prep
o Chemical feedback is localo Coeval epochs of PopII and PopIII star formation
Cosmic star formation history depends on chemical feedback
Chemical feedback
Japan-Italy meeting Niigata Dec 2-6 2003
PopII & PopIII star formation histories Chemical feedback parametrized as Eg = energy per unit gas mass in outflows
o efficiency of PopIII star formation f*III
o fraction of PISN (PopIII IMF)o efficiency of outflow generation fw
III
Scannapieco, RS & Ferrara (2003)
PopIII Stars
PopII Stars
Mean IGM Metallicity <Z> > Zcr @ z < 15
PopIII star formation ratepeaks @ z 10 and continues @ z < 10
Observational consequences
Japan-Italy meeting Niigata Dec 2-6 2003
Validation of the model & Observational consequences
o No Z=0 star found first generation of stars is very massive!o 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
Observational consequences
Extremely metal-poor halo stars as living fossils
The origin of HE0107-5240
Peculiar features:
[Fe/H] = -5.3 [C/Fe]= 4.0 [N/Fe] = 2.3
o What is the nature of the first (Z=0) stellar generation ? from observed elemental yields mass range of Z=0 SN
The star is a member of a second stellar generation
o 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
Observational consequences
Japan-Italy meeting Niigata Dec 2-6 2003
Observational consequences
A. Pre-formation C and N enrichment
(Umeda & Nomoto 2003)Zcloud Zcr
HE0107-5240
B. Post-formation C and N enrichment (RS, Ferrara,
Salvaterra, Omukai & Bromm 2003)
Zcloud Zcr
HE0107-5240
The origin of HE0107-5240 is consistent with Zcr criterium
PopIII footprints in the intracluster medium (ICM) Scannapieco, RS, Ferrara (2003)
Observational consequences
Japan-Italy meeting Niigata Dec 2-6 2003
i. Max 10% of the Cluster gas mass is processed through PopIII objects
ii. PISN heating is too low to account for the extra-energy required to match Lx-T
iii. Metal yields from PISN help reconcile the observed Fe and Si abundances
i. PISN can reproduce Fe/Mg data but not C/N data
ii. Stars with a Salpeter IMF can fit data
iii. Type Ia SNe are not required by data
PopIII Stars & Broad Line Regions of high-redshift QSOsVenkatesan, Schneider & Ferrara (2003)
In dense environments: i. Chemical feedback is strongii. Prompt transition from PopIII PopII
Conclusions
o First Stars are very massive
o Transition to “normal” stars regulated by metals and dust “critical metallicity”
o Interplay between PopIII stars and metal enrichment“chemical feedback”
o Chemical feedback is local: coeval PopIII and PopII/I
o Increasing number of observational constraints to improve/test the emerging scenario
Japan-Italy meeting Niigata Dec 2-6 2003