Radiative Feedback Effects of the First Objects in the Early Universe Kyungjin Ahn The University of Texas at Austin East-Asia Numerical Astrophysics Meeting Korean Astronomy and Space Science Institute Nov. 1, 2006

Outline No ionizing sources (Dark Ages) – 21cm radiation from minihalos and IGM First ionizing sources – Radiative feedback from a first star on nearby minihalos Late ionizing sources – UV Radiation background in the early universe

21cm Background from Cosmic Dark Ages (Shapiro, Ahn, Alvarez, Iliev, Martel, Ryu 2006 ApJL, 646, 681) Before Reionization - Cosmic Dark Ages  No appreciable light sources  Feeble 21cm radiation from neutral hydrogen  Hydrogen spin temperature decoupled from the CMB temperature by Ly pumping and/or collisions: 21cm emission/absorption against CMB  ;  With no radiation, collisional coupling inside minihalos and IGM is the only way for 21cm signal to be observed  Run cosmological N-body/hydro(TVD) simulation to quantify this signal: (500 h -1 Mpc) 3 comoving, grid, dark matter particles

Before Reionization - Cosmic Dark Ages  z<~20 T S  T K,IGM < T CMB mean IGM in absorption (T<0)  z>~20 minihalos start to emerge T S  T K,halo > T CMB in emission (T>0; T ~ a few mK)  What about clumpy IGM?

Summary  z<~20 mean IGM in absorption (T<0)  z>~20 minihalos start to emerge IGM clumping becomes significant in emission (T>0; T ~ a few mK) emission dominated by minihalos

Outline No ionizing sources (Dark Ages) – 21cm radiation from minihalos and IGM First ionizing sources – Radiative feedback from a first Pop III star on nearby minihalos Late ionizing sources – UV Radiation background in the early universe

Pop III Star Formation  Gas in minihalos (10 4 <M/M sun <10 8 ) can cool by H 2 cooling and form Pop III stars  Numerical LCDM simulations predict first Pop III stars formed in minihalos with M ~ 10 6 M z > ~20 (e.g. Bromm, Coppi, Larson 2002; Abel, Bryan, Norman 2002)  However, H 2 abundance is strongly affected by radiation. Negative feedback: Photo-dissociation  suppresses H2 formation; photo-heating  evaporation Positive feedback: Ionization  enhanced H 2 formation  Pop III star is (believed to be) massive, energetic, short- lived. (Maybe bimodal: Nakamura & Umemura 2001)

First H II Region by a Pop III Star: I-front trapping by minihalos  Alvarez, Bromm, Shapiro (2006) cosmological SPH simulation + I-front tracking I-front from a Pop III star being trapped by nearby minihalos  Minihalos are NOT flash-ionized! Further study required for the fate of the neutral core Radiative Feedback of a Pop III star on nearby Halos Flash-Ionized minihalos?  O'shea, Abel, Whalen & Norman (2005); Mesinger, Bryan, Haiman (2006) Assume full ionization of nearby halos of M~5*10 5 M solar Quick formation of H 2 Inner core collapses; Outer region evaporates

Radiative Feedback effects of the First Stars (Ahn & Shapiro 2006, MNRAS submitted, astro-ph/ ) Radiative Feedback Effects of the First Stars onto Nearby Collapsed Objects  Use 1-D Lagrangian, spherical, radiation-hydrodynamics code Full treatment of primordial chemistry, radiative transfer, cooling/heating, hydrodynamics  Follow I-front propagation of the radiation from outer, Pop III star in detail Is I-front trapped? What happens to the center? Any H 2 formation/dissociation interesting? Is it positive or negative feedback effect?  Compare to Susa & Umemura (2006)

A range of distances considered between the source and the target minihalos for different minihalo masses and also the evolutionary stages of the target minihalo when radiation arrives. Proper distances: D = 50, 180, 360, 540, 1000 pc Ionizing Photon Fluxes: F 0 = N ph,50 / r 2 kpc = 600, 46, 11, 5, 1.5 [i.e. N ph,50 (120 solar mass Pop III star) = 1.5] Minihalo masses: M / (10 5 solar mass) = 0.25, 0.5, 1, 2, 4, 5.5, 8 Initial evolutionary stages Phase I (no evolution)  mean IGM chemical z = 20  H 2 ~ 10 -6, e- ~ 10 -4, T core = T virial Phase II (evolved from Phase I for ~10 7 years < t Hubble )  H 2 ↑ as e- ↓ in core  H 2 ~ to 10 -3, e- ~  H 2 radiative cooling to T core ~ 100 K causes core to compress by factor ~ 1 to 20, higher for higher M

120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback target M=2e5 M sun

target M=2e5 M sun With no radiation: t coll =31 Myrs 120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback

target M=2e5 M sun With no radiation: t coll =31 Myrs With radiation: Flux F 0 =46.3 (D=180 pc) t coll =2.3 Myrs expedited collapse second star forms before the first star dies! 120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback

120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback target M=1e5 M sun

120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback target M=1e5 M sun With no radiation : t coll =89 Myrs

target M=1e5 M sun With no radiation : t coll =89 Myrs With radiation: Flux F 0 =46.3 (D=180 pc) t coll =129 Myrs delayed collapse second star forms after the first star dies, but still within a Hubble time 120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback

120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback (no H 2 self-shielding) target M=5.5e5 M sun located at D=50 pc

120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback (no H 2 self-shielding) 2 nd star forms in the merging halo after the first star dies (Abel, Wise & Bryan 2006)

120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback (no H 2 self-shielding) target M=5.5e5 M sun With no radiation : t coll =11 Myrs

target M=5.5e5 M sun With no radiation : t coll =11 Myrs With radiation Flux F 0 =600 (D=50 pc) t coll =47 Myrs delayed collapse second star forms after the first star dies,but still within a Hubble time 120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback (no H 2 self-shielding)

120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback (including H 2 self-shielding) target M=5.5e5 M sun

120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback (including H 2 self-shielding) target M=5.5e5 M sun With no radiation: t coll =11 Myrs

target M=5.5e5 M sun With no radiation: t coll =11 Myrs With radiation: Flux F 0 =600 (D=50 pc) t coll =1.1 Myrs expedited collapse second star forms before the first star dies! 120 solar mass Pop III star irradiates nearby minihalos at z=20: 1D, rad-hydro simulations of radiative feedback (including H 2 self-shielding)

Response to shock-front determines the fate of core expedited delayed

Response to shock-front determines the fate of core reversed unaffected

Radial Profiles at collapse

Summary Minihalos (target) nearby the first Stars (source) I-front trapped; Ionized gas evaporates; core remains neutral  Collapse, if any, doesn’t occur the way O’shea et al. have described, since they are NOT fully ionized in the beginning. Shock is driven to the neutral region: mixture of positive and negative feedback effects  Competition between H 2 cooling & shock-heating determines the fate of neutral region. Critical minimum mass for hosting 2 nd generation stars: 1-2 x 10 5 M sun  Susa & Umemura claim that shock delivers negative feedback only. We see positive feedback as well. Needs to be settled in higher resolution 3D simulations Overall, halos that are destined to collapse without Pop III stellar radiation would do so with radiation.  Phase I: After star dies, out of electrons that have not recombined yet, H 2 forms  Phase II: Electron is low, but H 2 is high such that the core is sufficiently self-shielded  + more complexity

Summary At collapse, unless the flux is very strong or mass of halo is very small, halo core profiles are identical to no-radiation case: protostellar mass is a weak function of flux Coeval formation of Pop III stars in the same neighborhood possible: H 2 self-shielding is crucial. Pop III stars may have fully reionized the universe (double reionization??) More things to consider  UV Background + Pop III starlight  Combined effect of wind, enrichment,..  HD chemistry (HD photo-dissociation not available though)

Outline No ionizing sources (Dark Ages) – 21cm radiation from minihalos and IGM First ionizing sources – Radiative feedback from a first star on nearby minihalos Late ionizing sources – UV Radiation background in the early universe

UV background in the Early Universe (Ahn, Shapiro, Iliev, in preparation) UV background at high redshift, especially in the H 2 Lyman- Werner band (dissociating photons), may control the formation of Pop III stars in the early universe  Haiman, Rees, Loeb; Haiman, Abel, Rees  Ricotti, Gnedin, Shull  Kitayama, Tajiri, Umemura, Susa, Ikeutshi  Kitayama, Susa, Umemura, Ikeutchi  Omukai, Nishii  Glover, Brand Cosmic reionization simulations  Iliev, Mellema, Shapiro, …  C 2 -ray method for hydrogen ionization front  Producing consistent results with reasonably assumed fudge factors (escape fraction, star formation efficiency, IMF, …)

Self-Regulated Reionization Iliev, Mellema, Shapiro, & Pen (2006), MNRAS, submitted; (astro-ph/ ) Jeans-mass filtering  low-mass source halos (M < 10 9 M solar ) cannot form inside H II regions ; 35/h Mpc box, radiative transfer simulation, WMAP3, f γ = 250; Big enough for statistical study resolved all halos with M > 10 8 M solar (i.e. all atomically-cooling halos), (blue dots = source cells); Evolution: z=21 to z ov = 7.5.

Time-slices of the reionization simulation (f γ = 2000) z =

UV background at high z Ahn et al., in preparation Status: H2 radiative transfer and chemistry added to C2-ray Mean and fluctuating H2 Lyman- Werner background at high-z, consistent with given model reionization history

Temperature at times t = 0.0, 0.2, 2.5, 10, 60, 150 Myrs. (M halo, z initial, F 0 ) = (10 7 M sun, 9, 1). Pop II source.