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

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

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

128 kpc comoving The Universe at Redshift 20

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

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 H 2 photo- dissociation

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 t chem and t h/c until the global min of t h/c is crossed (2) perform density and velocity updates (the hydro) every t h/c

Parameter Space of Surveyed Halos We sample consecutive evolutionary stages of a single 1.35 x 10 5 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

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

Evolution of Halo Cores in the Absence of Radiation

Halo Photoevaporation Model Grid

023_500pc: complete disruption

I-Front Structure monoenergetic: 10 5 K blackbody: quasar: mfp T-Front secondary ionizations by photoelectrons  e, T

Whalen et al 2008, ApJ, 682, 49 Whalen et al 2010, ApJ, 712, M sol 40 M sol 60 M sol 80 M sol 120 M sol

Local Radiative Feedback due to coeval nature of halos within the cluster, feedback tends to be positive or neutral halos with n c > 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

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

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

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

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

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

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

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)

Mixing & Fallback vs Mass, E ex, and Metallicity mixing falls and fallback rises with increasing mass mixing increases and fallback decreases with rising E ex mixing and fallback rise with metallicity

Elemental Yield Comparison to HMP Stars

IMF-Averaged Yields and the EMP Stars

Mixing in 150 – 250 M sol Pop III PI SNe Joggerst & Whalen 2011, ApJ, 728, 129

The Nucleosynthetic Imprint of 15 – 40 M sol 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

Thanks!