H II Regions of the First Stars II: A Primer on I-front Instabilities. Dan Whalen UC San Diego

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1 H II Regions of the First Stars II: A Primer on I-front Instabilities Dan Whalen UC San Diego

2 Our Collaboration Daniel Whalen, T-6, LANL; UC San Diego; UIUC Brian O Shea, T-6, LANL Alex Heger, T-6, LANL Michael Norman, UC San Diego

3 Ionization Front Evolution rapid initial bubble growth: R-type front with no gas motion R-type front slows due to recombinations and geometry pressure builds behind the front, breaking through it as a shock the front continues its expansion as D-type

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5 QuickTime and a YUV420 codec decompressor are needed to see this picture.

6 Current Status of ZEUS-MP Multispecies Radiative Transfer performs radiative transfer for a single point source in RTP geometry or can transport plane waves in XYZ or ZRP coordinates can solve non-equilibrium primordial chemistry with up to 9 species with radiative transfer fully coupled to hydrodynamics MPI parallelization scheme recently implemented and tested-- currently batched runs operate on 9, 25, and 36 processors with outstanding scaling out to 1024 processors multifrequency and Lyman-Werner physics upgrades are in currently in progress

7 Present Science Goals with ZEUS-MP 3D radiation hydrodynamical photoevaporation of cosmological minihalos hosting Pop III stars -- UV escape fractions from the first stars? -- enhanced chemical enrichment of the early IGM by supersonic outflows in primordial H II regions? -- 2nd generation structures and collapse of I-front instabilities? External photoionization of neighboring halos: positive or negative feedback effect on 2nd star formation?

8 A Brief History of I-front Instability Research 1D stability analyses of perturbations in planar fronts -- Kahn, Axford, Axford & Newman, Giuliani, 1979 Cometary structures formed by I-front shadowing by dense clumps (Bertoldi 1989, Canto et al 1998, Mellema et al 1998, Soker 1998) Thin shell breakup accelerated by D-type fronts (Garcia- Segura & Franco, 1996) Shadowing instabilities in R-type fronts (Williams, 1999) Long wavelength fragmentation of planar D-type fronts (Williams, 2002)

9 Thin Shell Instability Amplification by I-fronts Garcia-Segura & Franco ApJ, 469, 171, 1996 fragmentation of shocks that collapse into a thin shell by radiative cooling can occur in the absence of I-fronts but is worsened by them arise from imbalances between upstream ram pressure and isotropic downstream ionized gas pressure

10 2D axisymmetric density distribution: flat central core followed by an r -2 falloff: random density fluctuations dispersed throughout the volume ZEUS-3D hydro solver with ionization equilibria computed explicitly along all lines of sight no radiative transfer so no R-type I-fronts develop in these simulations

11 Shadowing Instabilities of R-Type Fronts Williams, MNRAS, 310, 789, 1999 mild overdensity or underdensity perturbs the radiation field--bertoldi s cloud-zapping regime (1989) I-front surface becomes crinkled but remains stable while R-type

12 Runaway to Non-Linearity the sides of the dimple in the I-front typically slow down first because of the flux is smallest there (photons strike the neutral interface at an angle) consequently, the front becomes D-type along the sides even as the rest of it races forward as R-type the abrupt exchange of the shock and the front along the sides of the depression elongate it into a tail as the entire I-front surface transforms to D-type it becomes subject to the thin shell dynamical instability: rapid breakup and fragmentation ensues

13 original perturbation UV flux is incident from the left (and was chosen to be comparable to an O-type star at a few pc) overdensities along adjacent lines of sight can exceed 10 4 fragmentation of the shock z Strom = 0.43 pc

14 Can the Numerics Deceive Us? zoning must resolve wavelengths of unstable modes smallest modes are of order of the recombination length in the ionized gas but are usually stabilized by recombinations zero wavelength odd-even numerical instability

15 Artificial Front Broadening

16 D-type Ionization Front Instabilities Williams, MNRAS, 331, 693, 2002 angle of incidence of the radiation crucially determines the stability of the front at normal incidence short wavelengths again saturate but long wavelength modes can catastrophically grow all wavelengths can be unstable if angle of incidence is nonzero

17 The Williams Wind Tunnel (the code is actually named Aqualung, and is a 2D AMR code--it has no radiative transport but instead employs ph source terms) Incident radiation gas inflow

18 Long-wavelength disruption of the D-type front

19 Applications to Minihalo Photoionization we expect that shadowing instabilities of the nascent R-type front will preempt any other type of instability although the D-phase of the I-front is short lived in most 1D simulations, neutral gas could persist over the main sequence lifetime of the central star because of the large overdensities that develop along some lines of sight during the front s transition from R- to D-type even low mass primordial stars could exhibit significant UV escape (and contribute metals to the early IGM) by channels created by instabilities--threshold effects seen by Kitayama, et al will probably go away clumping formed by instabilities possibly unstable to gravitational collapse? Especially if enriched by metals?--enzo/zeus-mp sims

20 Shadow Instability in an R-type Front: Density Evolution Whalen, Norman & Heger 2006 in prep QuickTime and a YUV420 codec decompressor are needed to see this picture.

21 Shadow Instability in an R-type Front: Temperature Evolution QuickTime and a YUV420 codec decompressor are needed to see this picture.

22 QuickTime and a YUV420 codec decompressor are needed to see this picture.

23 Future Work 3D cosmological minihalo photoevaporation 2nd star formation in relic H II regions energy injection by BH into the early IGM SN detonation in Pop III H II regions