Structure and Evolution of Cosmological HII Regions

1. Structure and Evolution of Cosmological HII Regions T. Kitayama (TohoUniversity) with N. Yoshida, H. Susa, M. Umemura

2. Introduction Feedback from the 1st stars in a Pop III objects - radiation - SN explosion ⇒ formation of HII regions (Yorke 1986) dissociation of molecules(Omukai & Nishi 1999) blow-away of gas (Ferrara 1998) metal enrichment (Gnedin & Ostriker 1997) etc. Great impacts on - reionization history - galaxy formation

3. Difficulties - Many relevant physical processes radiative transfer, non-equilibrium chemistry, explosive motions…. - Uncertain initial conditions density, temperature, velocity, composition….. This work 1D hydro + radiative transfer + H2 chemistry 　 ⇒　Evolution of HII regions around 1st stars for various Mhalo & ρ(r) Initial conditions for SN feedback studies

4. HII regions in a uniform medium (1) HII Static solution: photoionization = recombination ⇒Stroemgren sphere (1939) HII

5. HII regions in a uniform medium (2) Dynamical evolution formation of the HII region →pressure gap →shock →expansion of the HII region Two phases!

6. HII HII HII HII regions in a uniform medium (3) shock formation rion < Rst vion >> vshock rion > Rst vion ～ vshock R-type front D-type front

7. Essential ingredients: • hydrodynamics • radiative transfer • time-dependent • reactions • density profile • of the medium • etc. HII regions in a uniform medium (4) Rst

8. Method Collapsed cloud at z=10 in a ΛCDM universe total M → radius Rvir gas: power-law density profile n∝r-w Ti =1000K, Xe=10-4, XH2=10-4 DM: NFW profile (fixed) M,w: free Radiation from a central massive star 200 Msun, zero metallicity →Nγ(>13.6eV) = 2.3×1050 1/s Teff = 105 K τ= 2.2 Myr (Schaerer 2002) Solve 1D hydro, radiative transfer of UV photons, chemical reactions (e, H, H+, H-, H2, H2+,) & cooling/heating self-consistently

9. Structure of HII regions (1) n(r) ∝r-w, w=2 M=3×106 Msun high central density →confined I-front →sweep out of gas by shock →prompt ionization D-type →R-type opposite to the uniform medium

10. Structure of HII regions (2) n(r) ∝r-w, w=2 M=3×107 Msun higher mass → confined shock → no further ionization D-type only

11. Structure of HII regions (3) n(r) ∝r-w,w=1.5 M=3×107 Msun shallower slope ・lower n at the center ・higher n at the envelope R-type →D-type

12. n∝r-w w>3/2 ｎ ｎ ｎ∝Rst-3/2 ｎ∝Rst-3/2 n∝r-w w<3/2 ｒ ｒ Density profile and I-front types r<Rst →r>Rst r>Rst →r<Rst D-type →R-type R-type →D-type

13. Evolution of HII regions (1) I-front n(r) ∝r-w, w=2.0 M<107 Msun fully ionized H2 fully dissociated n0 < 1 cm-3 M>107 Msun almost unionized H2 partially dissoc. n0 > 30 cm-3 shock

14. Evolution of HII regions (2) I-front M=107 Msun w<1.5 fully ionized H2 fully dissociated n0 <1 cm-3 w>2.0 almost unionized H2 partially dissoc. n0 >10 cm-3 shock

15. Final HI and H2 fractions • Critical masses • - ionization • ～107 Msun • H2 dissociation • ～108 Msun H2 fraction positive feedback near Mcrit

16. Fate of collapsed clouds HI & H2 HI H2 dissociated HII

17. large: R-type small: D-type Fate of collapsed clouds HI & H2 HI H2 dissociated HII

18. n∝r-w w>3/2 ｎ ｎ ｎ∝Rst-3/2 ｎ∝Rst-3/2 n∝r-w w<3/2 ｒ ｒ Density profile and I-front types r<Rst →r>Rst r>Rst →r<Rst D-type →R-type R-type →D-type

19. Conclusions Radiative feedback from a massive star in Pop III objects →photoionized & photodissociated HII regions (M<107 Msun) (M<108 Msun) sweep-out of gas by shock down to n < 1 cm-3 Evolution & structure of HII regions sensitive to M & gas density profile (index w) w<1.5 : R-type → D-type w>1.5 : D-type → R-type maintenance/achievement of R-type front is essential!

20. Future work • Subsequent SN explosion • ← initial conditions from the present work • different z, Mstar, Zstar,….. • dust in HII regions • etc.