First Stars and Reionization Andrea Ferrara SISSA/International School for Advanced Studies Trieste, Italy Five Answers for Five Questions

Where did the first stars form ? First Question

Where did the first stars form ? Minimum Mass for Collapse ( t cool = t H ) Minimum Mass to Cool via H Lyα line  inimum Mass for Self-Shielding H 2 and the Radiative Feedback Ciardi etal 2000

Cooling/Star formation Efficiency z = 9 Madau, AF & Rees 2001 f b = M b (r < r cool ) M b (r < r vir ) Where did the first stars form ?

Were the first stars very massive ? Second Question

Infall Rate: 0.01 M o /yr Envelope: 10 3 M o Core:10 -2 M o

Salvaterra & AF 2002; Salvaterra & AF 2002; Best fit model to NIR data: z end = 8.8 f  = 4% IR Background Data Points Pop III stars can explain observed NIRB excess if VMS dominate IMF ~ (1+z end ) λ Lyα PopIII Stars Were the first stars very massive ? Magliocchetti, Salvaterra & AF 2003 Magliocchetti, Salvaterra & AF 2003

When did the transition to normal stars occur? Third Question

Schneider, AF, Natarajan, Omukai 2002 Critical Metallicity for IMF Transition: Z O Z O 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 2003 Reionization after WMAP A Conservative Model: No “exotica” G Maximum H 2 /UV feedback: no stars in minihalos G Smallest star-forming halos M = 5×10 8 M O G Moderately heavy IMF: Larson, M c = 5 M O G No Very Massive Stars, but metal-free G Maximum Escape Fraction, f esc = 20% Which stars did ionize the universe ?

Ciardi, 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-effect requires 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

n H T Z Z III z = 50 z = 20 z = 8 z = 5 z = 4 z = 3

Bruscoli etal 2003 The z  3: a Closer View Temperature Metallicity Z > Z cr Z  0 Where should we look for the first stars ?

Scannapieco, Schneider & AF 2003 Scannapieco, Schneider & AF 2003 Lyα Detection Probability E g  Kinetic Energy / Baryon Mass into Stars E g  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 ~ Z O 5. Where should we look for the first stars ? Try hard with Lya emitters

Magliocchetti, Salvaterra & AF 2003 Magliocchetti, Salvaterra & AF 2003 Were the first stars very massive ?

Z = Z o Redshift z = 28 Z = Z o Redshift z = 22, AF, Coppi & Larson 2001 Bromm, AF, Coppi & Larson 2001 Vigorous fragmentation Low mass clumps Limited fragmentation High mass clumps M = 1000 M O M = 10 M O When did the transition to normal stars occur ?

Scannapieco, AF & Madau Songaila < log N HI < 15 f * =10% Filling factor : z = 3 Large objects M>10 9 M 0 contribute < 1% Flat metallicity evolution upto z = 8 due to decreasing f ej of larger galaxies Pettini etal 2003 Where should we look for the first stars ?

Were the first stars very massive ? Living Fossils ? How many PopIII stars ended up in our Galaxy ? What is their metallicity distribution ? What can we learn on their Initial Mass Function ? Larson IMF mm   (m) Hernandez & AF 2001 Jeans mass corresponding to CMB temperature ΛCDM Characteristic Stellar Mass was Larger in the Past

An Emerging Scenario Redshift 0369 M  /M O /Z 0 VMS/VMBH Era Transition to Normal IMF Normal IMF Reionization Required by NIRB data Required by QSO data High-z GRBs SNII PopIII host candidates SN γγ ?