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