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Understanding the Formation and Impact of the First Stars in the Universe

This comprehensive study delves into five key questions regarding the origins and effects of the first stars in the universe. It explores where these stars formed, their mass characteristics, the transition to "normal" stars, the stars responsible for reionizing the universe, and potential locations for observing the first stars. Drawing on historical data and models, the research highlights factors like H2 cooling, metallicity, and the role of massive stars, providing insightful answers to each critical inquiry.

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Understanding the Formation and Impact of the First Stars in the Universe

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

  2. Where did the first stars form ? First Question

  3. Minimum Mass to Cool via H Lyα line Minimum Mass for Self-Shielding Minimum Mass for Collapse ( tcool = tH ) Where did the first stars form ? Ciardi etal 2000 H2 and the Radiative Feedback

  4. Mb(r < rcool) fb = Mb(r < rvir) Where did the first stars form ? Madau, AF & Rees 2001 Cooling/Star formation Efficiency z = 9

  5. Were the first stars very massive ? Second Question

  6. Envelope: 103 Mo Core:10-2 Mo Infall Rate: 0.01Mo/yr

  7. ~ (1+zend ) λLyα Were the first stars very massive ? Salvaterra & AF 2002; Magliocchetti, Salvaterra & AF 2003 IR Background Data Points Best fit model to NIR data: zend = 8.8 f = 4% PopIII Stars Pop III stars can explain observed NIRB excess if VMS dominate IMF

  8. When did the transition to normal stars occur? Third Question

  9. Critical Metallicity for IMF Transition: 10-6 ZO10-4 ZO When did the transition to normal stars occur ? Schneider, AF, Natarajan, Omukai 2002 Chemical Feedback

  10. Which stars did ionize the universe ? Fourth Question

  11. Which stars did ionize the universe ? z = 17 NIRB Fitting Evolution

  12. Which stars did ionize the universe ? Ciardi, AF & White 2003 Reionization after WMAP A 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%

  13. 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

  14. Double Reionization ? 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 L20

  15. Where should we look for the first stars ? Fifth Question

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

  17. 1% 3% 10% Where should we look for the first stars ? Scannapieco, Schneider & AF 2003 Lyα Detection Probability Eg Kinetic Energy / Baryon Mass into Stars EgFeedback Parameter

  18. 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 Summary

  19. An Emerging Scenario VMS/VMBH Era Transition to Normal IMF Normal IMF Reionization ? . . . . . . <Z>/Z0 . . Required by NIRB data . . . . . . 10- 0.5 . . . 103 . . 10- 2.5 . . . . . Required by QSO data . . . . . SNII . High-z GRBs . . M/MO SNγγ . . . 100 . . . . . 10- 1 . PopIII host candidates 10- 5 9 6 3 0 Redshift

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