Formation of the First Stars Under Protostellar Feedback

1. Formation of the First Stars Under Protostellar Feedback Athena Stacy First Stars IV 2012

2. Collaborators • Volker Bromm (U.Texas) • Andreas Pawlik (U. Texas) • Thomas Greif (MPA) • Avi Loeb (Harvard/CfA)

3. Dark Ages

4. Open Questions • What role did they play in reionization and metal enrichment? - What feedback did they exert on later star formation? (Pop III to Pop II transition) This depends on the Pop III IMF, SFR, and rotation rates… • What were their typical masses? • What was their typical multiplicity? - When will a Pop III protostar’s accretion become shut off by feedback ? or or ???

5. I. Pop III Star Formation Without Feedback Stacy, Greif, & Bromm, 2010 MNRAS, 403, 45

6. Cosmological simulation: • Gadget (SPH + N-body) • initialized at z=100 according to CDM model • followed formation of protostar (sink particle) and subsequent 5000 yr of accretion • msph (gas) = 0.015 M • Mres ~ 1.5Nneighmsph ~ 1 M • = minimum allowed Jeans mass ???

7. Initial Collapse minihalo sink IGM (time) 3-body reactions and H2 formation

8. Sink Particles • Msink = 1 M • n = 1012 cm-3 • racc ~ 50 AU ~ 1015 cm • R ~ 1011 cm  Density no longer evolved • Accrete gas particles that fall within racc of sink  By using sink particles, we can continue following evolution of star-forming gas for thousands more years (~ 100 freefall times)! 50 AU

9. Pop III stars can form in multiples! 5000 AU Density [cm-3] Multiple stars form within a disk that has grown to ~ 40 M (tacc = 5000 yrs)

10. Binary and Multiple Formation • Toomre Fragmentation criterion: • Q ~ 0.4 < 1 • tcool < trot and (Gammie 2001, Kratter et al. 2010, 2011) • Multiple sinks form through disk fragmentation

11. Rapid Pop III Accretion Rates Sink A: Msink ~ t0.5 dM/dt ~t-0.5 sink A B&L 2004 Sink B: Msink ~ t0.25 dM/dt ~t-0.75 sink B Mfinal > 100 M

12. II. Pop III Star Formation With Radiative Feedback Stacy, Greif, & Bromm, 2012, MNRAS, 422, 290

13. Protostellar Feedback • Repeat previous cosmological simulation, but with updated H2 cooling rates (Sobolev approximation) • Model LW radiation and growth of surrounding HII region • Also performed a comparison “no-feedback” simulation • How will radiation alter the growth of the Pop III star?

14. -200 radial segments -105 angular sements -107 bins M* = Msink R* = ? The I-front Tracker

15. The Protostellar Model Hosokawa et al. 2010

16. KH contraction KHcontraction Adiabaticexpansion ZAMS Adiabatic accretion ZAMS Hosokawa et al. 2010

17. The Protostellar Model M*=Msink Adiabatic expansion KH contraction Slow contraction model Simulation model ZAMS

18. I-front breakout M* = 15 M Ionization rate Mass infall rate

19. I-front Evolves in Morphology 1500 yr 2500 yr 4500 yr

20. Temperature Structure Without feedback 2500 yr 2500 yr 5000 yr Sink potential well heating I-front Warm neutral bubble 3000 yr 2500 yr 4000 yr With feedback

21. With Feedback * = main sink + = secondary sink

22. Feedback Slows Disk Growth No feedback With feedback Envelope = gas with n>108 cm-3

23. Without Feedback Density, x-y plane Disk disrupted by N-body dynamics Density, x-z plane Temperature, x-y plane Temperature, x-z plane Box = 10,000 AU

24. Reduced Accretion Rate Without feedback Msink~ t0.13 With feedback Msink~ t0.09 2nd largest sink (with feedback) Mfinal ~ 30 M

25. III. Pop III Formation Under Dark Matter Effects? Stacy, Pawlik, Bromm, & Loeb 2012, MNRAS, 421, 894

26. WIMP annihilation important for Pop III stars? Can it heat SF gas, or replace/supplement nuclear fusion? (www.nasa.gov, Sky and Telescope, Gregg Dinderman)

27. Pop III stars form in regions of high DM density

28. May lead to extremely massive and luminous Pop III stars a.k.a. “dark stars” -R* ~ 1 AU -Teff too low to ionize -Accretion unimpeded for long time (e.g., Freese et al. 2008, Spolyar et al. 2008, Iocco et. al 2008, Natarajan et al. 2009)

29. DM heating and capture rates 1. DM heating  delayed protostellar contraction  prolonged accretion (M* reaches 105 M?) 2. DM capture by MS star  burn DM instead of hydrogen  prolonged stellar lifetime (to z=0?) Higher DM density  greater effect on gas and stars

30. But will this work in a Pop III MULTIPLE system?

31. New DM Initialization 1. Begin simulation immediately after the first sink has formed 2. Align DM peak with main sink 3. Continue simulation for 20,000 yr How will these DM profiles evolve? Will density stay peaked?

32. Decline of DM Density on Stellar Disk Scales Minimum DM density for DM capture to support a star 10,000 yr 10,000 yr 20,000 yr 20,000 yr Sinks and DM density peak UNALIGNED

33. Rapid Decline of DM Effect on Gas and Stars Blue – DM capture rate within sinks (-> DM density) Black – DM heating rate within sinks (-> DM density2)

34. Pop III Mass Growth Relatively Unaffacted DM unrefined Sim B Sim A

35. Conclusions • Range of Pop III masses is likely very broad. • Multiple mechanisms, particularly disk fragmentation, will contribute to formation of low mass stars. • Fragmentation and broad mass range likely to describe Pop III stars even under radiative feedback! Possibly massive binaries • Pop III stars can likely reach tens of solar masses, but hundreds of solar masses may be harder (see also Susa and Hosokawa’s talks)  Maybe explains why PISN signature has not been observed (requires 140M < M* < 260M) • Pop III multiplicity will strongly mitigate effects of DM annihilation - ‘dark stars’ unlikely (see also Smith’s poster and Iocco’s talk) • Growing understanding of Pop III stars will ultimately increase physical realism of models of later star and galaxy formation

36. Questions?

37. THE END Thank you!