Seattle 2006, summer

RHD Simulations on the Radiative Feedback

from First Stars

Hajime Susa Rikkyo University, Japan

Seattle 2006, summer

Radiative feedback

• H2 dissociation (Negative)– By nearby star– Background

• Ionization ( Positive & Negative )– Photoevaporation– Increase the catalysts for H2 formation– H2 shell formation

Abel et al 2006

Seattle 2006, summer

23/ 4

,0 14 -210 cmH

LW LWN

L L-æ ö÷ç= ÷ç ÷çè ø

( )2

126 2

20.88 10 ( )4LW

H eLn x T nrp

--= ´ equi l i br i um

( ) ( ) ( )11 23,03 3

4 24 -1 -1 3 -31kpc10 10 erg s Hz 10 K 1cm

LWesh

Lx T nr-- -

-

æ ö÷ç ÷ç= ÷ç ÷ç ÷ç ÷è ø

H2 photodissociation feedback in uniform gas cloud

Uniform low mass host clouds are totally Photodissociated by single POPIII star.

Omukai & Nishi 1999

Seattle 2006, summer

H2 photodissociation feedback on clumpy cloud

• Dynamically collapsing cloud ?• Photoionization?

Glover & Brand 20013 -3

crit 100pc@ 10 cmclumpD n »;

Dense clouds are able to survive the photodissociation feedback by another nearby star. dis fft t<

dis fft t>

Seattle 2006, summer

Numerical Methods

• Tree • SPH• RT of Ionizing photons by Ray Tracing• RT of Lyman-Werner photons by Ray Tracing

( Self-Shielding function)

• Implicit solver for reactions and energy equation• H2 (no He) • Everything parallelized utilizing MPI

( ) 22 2

3/ 414 2

14 2 if 1010

HLW sh H H

NF f N N cm

cm

--

-æ ö÷çµ = >÷ç ÷çè ø

H. Susa, PASJ 58, 445 (2006)

Seattle 2006, summer

First model of FIRST Cluster(Univ. of Tsukuba)

• 16 nodes (32 Xeon )• Gbit network• 16 Blade GRAPE

Blade-GRAPE

FIRST 16-node

Seattle 2006, summer

Setup

SPH particlesUniformly Distributed

48.3 10 M´3

clump 10cmn -=

3env 0.1cmn -=Uniform

dense clump

Run-away collapsing Core

pcD

(center)H onn n>

Turn on the nearby star

Seattle 2006, summer

Parameters524288SPHN =

Property of the Source Star

120M 49.92 10 K´4.6R

with/ without ionizing photons

2.5pc 140pcD = -

2 5 310 10 cmonn -= :

Seattle 2006, summer

Failed Collapse ( H2 fraction )3 -3

on 10 cm

40pc

n

D

=

= LW photons sweep the dense core and prevent the cloud from collapsing.

Core bounce

Seattle 2006, summer

Survived prestellar core (H2 fraction) 3 -3

on 10 cm

100pc

n

D

=

=

Collapsed core

H2 is self-shielded

Seattle 2006, summer

Time evolution of Central density

collapse

bounce

Turn-on

Seattle 2006, summer

Evolution of central density & tempetarute

Bounce

Thre

e di

ffer

ent i

nitia

l Tof

col

laps

ing

clou

d

We need some explanation

collapse

Seattle 2006, summer

Analytic argument (Susa 2006 in prep.)

• In the presence of strong LW intensity, H2 are in chemical equilibrium.

• H2 number density can be assessed with given density temperature, and LW flux.

• H2 cooling rate can be assessed with given density temperature, and LW flux.

• We can evaluate the cooling condition of the core by t_ff > t_cool (Condition like Rees & Ostriker )

Seattle 2006, summer

Ionized fraction is out of equilibrium

2 3/ 2323

pe erec e

Gmdy dy dt nk y ndn dt dn π

−= −

But we have analytic solution….

1 00 0

0

1

2( / 1)e

rece

ff

y ty n nt

−=

+ − Function of density

Seattle 2006, summer

H2 fraction in equilibrium

Seattle 2006, summer

Cooling condition

Once the collapsing core satisfy above condition, the collapse cannot be stopped.

Seattle 2006, summer

Bounce

RUN AWAY REGION

Susa, in preparation (2006)

D=20pc

collapse

Seattle 2006, summer

D=80pc

collapse

Bounce

RUN AWAY REGION

Seattle 2006, summer

Summary 1• We perform 3D RHD simulations for the radiative feedback effects on primordial star formation.

• Prestellar core could survive the LW flux, if the core density and temperature satisfy the cooling condition written by an analytic formula.

Seattle 2006, summer

Ionization + dissociationSusa & Umemura ApJL in press (2006)

Seattle 2006, summer

3 typical models

• Model A: non = 3x103 cm-3 , No ionizing photons (for comparison)

• Model B: non = 3x103 cm-3 , ionization• Model C: non = 3x102 cm-3 , ionization

• M*=120Msun , D=20 pc for all models

Seattle 2006, summer

Snap shots610-

y2H

yHIHn

T

810- 410-

410

410−

810−

1

Model A Model B Model C

T

Hn

yHIy

2H

410

410−

810−

1

THn

yHI

142H ,Ny

2H

10 200 10 200 10 200

142H ,N 142H ,N

Bounce collapse blown away

Seattle 2006, summer

Effects of ionizing photons

• Low density clump : – Photoheating– →Photoevaporation

• High density clump:– H2 shell formation– →Enhance the shielding of LW radiation– →collapse promoted

Seattle 2006, summer

Collapse criteria for core density-3

-3

-3

pc : cmpc : cmpc : cm

3

2

20 10

30 10

50 10

on

on

on

D n

D n

D n

=

=

=

t

t

t

If we consider non > 103 cm-3 ,(�tff < tpopIII) negative radiative feedback by nearby star is unlikely.

Seattle 2006, summer

Summary 2 • We perform 3D RHD simulations for theradiative feedback effects on primordial star formation.

• Ionization blow out the low density cloud (n < 10cc, if D=50pc).

• But it helps to form stars for dense clouds by H2 shell formation.

• Realistic density field as well as force of gravity by dark matter……… we need more simulations.

Seattle 2006, summer

FIRST

256 �16×16�nodes512 CPU �

256 Blade-GRAPE

512 Xeon : 2.9 Tflops

Blade-GRAPE: 8.7 Tflops

Memory: 512GB

Will be available in September, 2006