Structure and evolution of cosmological hii regions
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Structure and Evolution of Cosmological HII Regions. T. Kitayama (Toho University) with N. Yoshida, H. Susa, M. Umemura. Introduction. Feedback from the 1st stars in a Pop III objects - radiation - SN explosion. ⇒ formation of HII regions (Yorke 1986)

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Structure and Evolution of Cosmological HII Regions

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Structure and evolution of cosmological hii regions

Structure and Evolution of Cosmological HII Regions

T. Kitayama (TohoUniversity)

with

N. Yoshida, H. Susa, M. Umemura


Introduction

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


Difficulties

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


Hii regions in a uniform medium 1

HII regions in a uniform medium (1)

HII

Static solution:

photoionization

= recombination

⇒Stroemgren sphere

(1939)

HII


Hii regions in a uniform medium 2

HII regions in a uniform medium (2)

Dynamical

evolution

formation of

the HII region

→pressure gap

→shock

→expansion of

the HII region

Two phases!


Hii regions in a uniform medium 3

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


Hii regions in a uniform medium 4

Essential

ingredients:

  • hydrodynamics

  • radiative transfer

  • time-dependent

  • reactions

  • density profile

  • of the medium

  • etc.

HII regions in a uniform medium (4)

Rst


Method

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


Structure and evolution of cosmological hii regions

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


Structure and evolution of cosmological hii regions

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


Structure and evolution of cosmological hii regions

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


Density profile and i front types

n∝r-w

w>3/2

n∝Rst-3/2

n∝Rst-3/2

n∝r-w

w<3/2

Density profile and I-front types

r<Rst →r>Rst

r>Rst →r<Rst

D-type →R-type

R-type →D-type


Evolution of hii regions 1

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


Evolution of hii regions 2

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


Final hi and h 2 fractions

Final HI and H2 fractions

  • Critical masses

  • - ionization

  • ~107 Msun

  • H2 dissociation

  • ~108 Msun

H2 fraction

positive feedback

near Mcrit


Fate of collapsed clouds

Fate of collapsed clouds

HI & H2

HI

H2 dissociated

HII


Fate of collapsed clouds1

large: R-type

small: D-type

Fate of collapsed clouds

HI & H2

HI

H2 dissociated

HII


Density profile and i front types1

n∝r-w

w>3/2

n∝Rst-3/2

n∝Rst-3/2

n∝r-w

w<3/2

Density profile and I-front types

r<Rst →r>Rst

r>Rst →r<Rst

D-type →R-type

R-type →D-type


Conclusions

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!


Future work

Future work

  • Subsequent SN explosion

  • ← initial conditions from the present work

  • different z, Mstar, Zstar,…..

  • dust in HII regions

  • etc.


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