Radiative and Chemical Feedback by the First Stars

1. Radiative and Chemical Feedback by the First Stars Daniel Whalen McWilliams Fellow Carnegie Mellon University

2. My Collaborators • Joe Smidt (UC Irvine) • Thomas McConkie (BYU) • Brian O’Shea (MSU) • Mike Norman (UCSD) • Rob Hueckstaedt (LANL)

3. Numerical Simulations of Local Radiative Feedback on Early Star Formation Uniform Ionizing/LW Backgrounds Rad Hydro Models of Single Halos • Machacek, Bryan & Abel 2001, • MNRAS, 548, 509 • Machacek, Bryan & Abel 2003, • MNRAS, 338, 273 • O’Shea, Abel, Whalen & Norman • 2005, ApJL, 628, 5 • Mesinger, Bryan & Haiman 2006, • ApJ, 648, 835 • Mesinger, Bryan & Haiman 2009, • MNRAS, 399, 1650 • Susa & Umemura 2006, • Ahn & Shapiro 2007, MNRAS, • 375, 881 • Whalen et al 2008, ApJ, 679, • 925 • Whalen, Hueckstaedt & • McConkie 2010, ApJ 712,101

4. The Universe at Redshift 20 128 kpc comoving

5. ZEUS-MP Reactive Flow Radiation Hydrodynamics Code • massively-parallel (MPI) Eulerian hydrocode with 1-, 2-, • or 3D cartesian, cylindrical, or spherical meshes • 9-species primordial H/He gas network coupled to photon • conserving multifrequency UV transfer • Poisson solver for gas self-gravity • includes the dark matter potential of cosmological halos, • which remains frozen for the duration of our calculations

6. 40 energy bins < 13.6 eV, 80 bins from 13.6 eV to 90 eV • self-shielding functions of DB 96 corrected for thermal • Doppler broadening are used to compute H2 photo- • dissociation

7. Adaptive Subcycling • three characteristic timescales emerge when one couples • radiation to chemistry and hydrodynamics: • the trick is to solve each process on its own timescale without • holding the entire algorithm hostage to the shortest time step • procedure: • (1) while holding densities and velocities fixed, evolve • reaction network and gas energy on global min of tchem • and th/c until the global min of th/c is crossed • (2) perform density and velocity updates (the hydro) every • th/c

8. Parameter Space of Surveyed Halos • We sample consecutive evolutionary stages of a single • 1.35 x 105 solar mass halo rather than the entire cluster • at a single redshift • Since halos in the cluster tend to be coeval, exposing • just one at several central densities spans the range of • feedback better than a few at roughly the same density • We chose this halo mass because it is the smallest in • which we expect star formation, so feedback would be • less prominent than in a more massive halo

9. Spherically-Averaged Enzo AMR Code Halo Radial Density and Velocity Profiles (O’Shea & Norman 2007b) z = 23.9, 17.7, 15.6 and 15.0

10. Evolution of Halo Cores in the Absence of Radiation

11. Halo Photoevaporation Model Grid

12. 023_500pc: complete disruption

16. I-Front Structure monoenergetic: 20 - 30 mfp e, T 105 K blackbody: e, T T-Front quasar: e, T secondary ionizations by photoelectrons

19. 25 Msol 40 Msol 60 Msol Whalen et al 2008, ApJ, 682, 49 Whalen et al 2010, ApJ, 712, 101 80 Msol 120 Msol

20. Local Radiative Feedback • due to coeval nature of halos within the cluster, feedback • tends to be positive or neutral • halos with nc > 100 cm-3 will survive photoevaporation • and host star formation (accelerated in many instances) • feedback sign is better parameterized by central halo • density than halo mass • radiation drives chemistry that is key to the hydrodynamics • of the halo -- multifrequency transfer is a must • these results are mostly independent of the spectrum of • the illuminating star--more LW photons don’t make much • difference

21. Nucleosynthetic Forensics of the First Stars Daniel Whalen Candace Joggerst 2010, ApJ, 709, 11 2011, ApJ, 728, 129

22. Our Collaborators • Ann Almgren (LBNL) • John Bell (LBNL) • Alexander Heger (University of Minnesota) • Stan Woosley (UC Santa Cruz)

23. The Primordial IMF Remains Unconstrained Numerical simulations, although proceeding from well-posed initial conditions, lack the physics to model star formation up to the main sequence (and likely diverge from reality well before) Direct observation of primordial supernovae, in concert with gravitational lensing, may be possible with JWST (Kasen & Woosley 2010; Whalen et al 2011a,b,c, in prep) Stellar archaeology, in which we search for the nucleosynthetic imprint of Pop III stars on low-mass subsequent generations that survive today, is our best bet for indirectly constraining the primordial IMF

24. Final Fates of the First Stars Heger & Woosley 2002, ApJ 567, 532

25. Stellar Archaeology: EMP and HMP Stars • Hyper Metal-Poor (HMP) Stars: • -5 < [Fe/H] < -4  thought to be enriched by one or • a few SNe • Extremely Metal-Poor (EMP) Stars: • -4 < [Fe/H] <-3  thought to be enriched by an entire • population of SNe because of the • small scatter in their chemical • abundances

26. No PISN? • original non-rotating stellar • evolution models predict a • strong ‘odd-even’ nucleosynthetic • signature in PISN element • production • to date, this effect has not been • found in any of the EMP/HMP • surveys • intriguing, but not conclusive, • evidence that Pop III stars had • lower initial masses than suggested • by simulation • this has directed explosion models • towards lower-mass stars Heger & Woosley 2002

27. 2D Rotating Progenitor Pop III Explosion Models • progenitors evolved in the 1D KEPLER • stellar evolution code, exploded, and then • followed to the end of nucleosynthetic burn • (~ 100 sec) • KEPLER profiles then mapped into the new • CASTRO AMR code and then evolved in 2D • out to shock breakout from the star • 2 rotation rates, 3 explosion energies, 3 • masses, and 2 metallicities, for a total of 36 • models • self-gravity of the gas plus the gravity of the • compact remnant (the latter is crucial for • capturing fallback) CASTRO Code (Almgren et al 2009)

28. Mixing & Fallback vs Mass, • Eex, and Metallicity • mixing falls and fallback rises • with increasing mass • mixing increases and fallback • decreases with rising Eex • mixing and fallback rise with • metallicity

29. Elemental Yield Comparison to HMP Stars

30. IMF-Averaged Yields and the EMP Stars

31. Mixing in 150 – 250 Msol Pop III PI SNe Joggerst & Whalen 2011, ApJ, 728, 129

32. The Nucleosynthetic Imprint of 15 – 40 Msol Pop III Stars on the First Generations • 15 – 40 M rotating Pop III progenitors are a good fit to one of the • HMP chemical abundances but not the other two • an IMF-average of the chemical yields of our zero-metallicity models • provides a good fit to the abundances Cayrel et al 2004 and Lai et al • 2008 measured in their EMP star surveys • since EMP stars are imprinted by well-established populations of • SNe, they are a better metric of primordial SN progenitors • direct comparison of nucleosynthetic yields from numerical models • to the abundances of MP stars is problematic—intervening • hydrodynamical processes complicate elemental uptake into new • stars • newly completed surveys (like SEGUE-II) will greatly expand our sample • of metal-poor stars and yield great insights into the primordial IMF

33. Thanks!