Radiative Feedback by the First Stars Dan Whalen, T-2, LANL

Radiative Feedback bythe First Stars

Dan Whalen, T-2, LANL QuickTime™ and aTIFF (Uncompressed) decompressor

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Whalen et al 2008, ApJ, 679, 925Hueckstadt & Whalen, ApJ, in prep

Our Collaboration

Daniel Whalen, T-2, LANL

Rob Hueckstaedt, X-2, LANL

Brian O’Shea MSU

Joseph Smidt UC Irvine

Alex Heger U Minn

Michael Norman, UC San Diego

~ 200 pc

CosmologicalHalo z ~ 20

H2 Formation Pathwaysin High Redshift Cosmological

Minihalos

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128 kpc comoving

The Universeat 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

• adaptive time step hierarchy enforces respective Courant, heating, and chemistry times without holding the entire algorithm hostage to the shortest time scale

• Poisson solver for gas self-gravity

• a separate array serves as a proxy for the dark matter potential, which remains frozen in the course of these 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 H2 photo- dissociation

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

Spherically-Averaged Enzo AMR Code Halo Radial Density andVelocity 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

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I-Front Structure

monoenergetic:

105 K blackbody:

quasar:

20 - 30 mfp

T-Front

secondary ionizations by photoelectrons

e, T

e, T

e, T

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059_500pc

Four Fates of Satellite Halos

• complete core disruption

• undisturbed cores

• accelerated collapse

• core drainage/partial disruption

023_500pc: complete disruption

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40 solar mass star

059_500pc

40 solar massstar

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Four Outcomes:

• halos with nc < 2 - 3 cm-3 are completely destroyed anywhere in the cluster• halos with nc > 1000 cm-3 are insulated from radiation--collapse is unaffected• star formation in halos of intermediate density can be accelerated or delayed depending on how the shock and shadow squeeze the core

Preliminary Conclusions

• 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