Radiative Feedback by the First Stars Dan Whalen, T-2, LANL
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Transcript of Radiative Feedback by the First Stars Dan Whalen, T-2, LANL
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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
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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
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~ 200 pc
CosmologicalHalo z ~ 20
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H2 Formation Pathwaysin High Redshift Cosmological
Minihalos
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128 kpc comoving
The Universeat Redshift 20
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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
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• 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
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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
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Spherically-Averaged Enzo AMR Code Halo Radial Density andVelocity Profiles (O’Shea & Norman 2007b)
z = 23.9, 17.7, 15.6 and 15.0
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Evolution of Halo Cores in the Absence of Radiation
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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
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Four Fates of Satellite Halos
• complete core disruption
• undisturbed cores
• accelerated collapse
• core drainage/partial disruption
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023_500pc: complete disruption
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40 solar mass star
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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
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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