First Stars and Reionization

Andrea Ferrara

SISSA/International School for Advanced StudiesTrieste, Italy

Five Answers for Five Questions

Where did the first stars form ?

First Question

Where did the first stars form ?

Minimum Massfor Collapse ( tcool = tH )

Minimum Mass toCool via H Lyα line inimum Mass

for Self-Shielding

H2 and the Radiative Feedback

Ciardi etal 2000Ciardi etal 2000

Cooling/Star formation Efficiency

z = 9

Madau, AF & Rees 2001Madau, AF & Rees 2001

fb = Mb(r < rcool)

Mb(r < rvir)

Where did the first stars form ?

Were the first stars very massive ?

Second Question

Infall Rate: 0.01 Mo/yr

Envelope: 103 Mo

Core:10-2 Mo

Salvaterra & AF 2002;Salvaterra & AF 2002;

Best fit model to NIR data:

zend = 8.8f = 4%

IR Background Data Points

Pop III stars can explain observed NIRB excess

if

VMS dominate IMF ~ (1+zend ) λLyα

PopIII Stars

Were the first stars very massive ?

Magliocchetti, Salvaterra & AF 2003Magliocchetti, Salvaterra & AF 2003

When did the transition to normal stars occur?

Third Question

Schneider, AF, Natarajan, Omukai 2002

Critical Metallicity for IMF Transition:

10-6 ZO 10-4 ZO

When did the transition to normal stars occur ?

Which stars did ionize the universe ?

Fourth Question

z = 17

NIRB Fitting Evolution

Which stars did ionize the universe ?

Ciardi, AF & White 2003Ciardi, AF & White 2003

Reionization after WMAPA Conservative Model: No “exotica”

Maximum H2/UV feedback: no stars in minihalos

Smallest star-forming halos M = 5×108 MO

Moderately heavy IMF: Larson, Mc = 5 MO

No Very Massive Stars, but metal-free

Maximum Escape Fraction, fesc = 20%

Which stars did ionize the universe ?

Ciardi, AF & White 2003Ciardi, AF & White 2003 Reionization after WMAP

z = 17.6 z=15.5 z=13.7

Larson IMF

Salpeter IMF

Which stars did ionize the universe ?

Light from First Galaxies

Optical Depth Evolution

Reconciling with GP-effectrequires a subsequent drop

of the ionizing power

No contribution to optical depth in 6 <z < 9: still within WMAP error box

Double Reionization ?

L20

Where should we look for the first stars ?

Fifth Question

Bruscoli etal 2003Bruscoli etal 2003

The IGM @ z 3: a Closer View

Temperature Metallicity

Z > Zcr

Z 0

Where should we look for the first stars ?

Scannapieco, Schneider & AF 2003Scannapieco, Schneider & AF 2003

Lyα Detection Probability

Eg Kinetic Energy / Baryon Mass into Stars

Eg Feedback Parameter

1%

3% 10%

Where should we look for the first stars ?

Summary

1. Where did the first stars form ?In Lya-cooled haloes

2. Were the first stars very massive ?Very likely, yes

3. Which stars did ionize the universe ?Normal stars, although extra contribution from massive ones

4. When did the transition to normal stars occur? Whenever/Wherever Z ~ 10 -5 ZO

5. Where should we look for the first stars ?Try hard with Lya emitters

An Emerging Scenario

Redshift0369

M/MO

<Z>/Z0

VMS/VMBH Era

Transition to Normal IMF

Normal IMF

10- 5

10- 2.5

10- 0.5

103

10- 1

100

Reionization

Required by NIRB data

Required by QSO data

High-z GRBsSNII ..

....

.

...

...... .

.

....

. ..

. .

.

.

.... ...

.

..

.

.PopIII host candidates

SNγγ

?