Growth of massive seed
BHs in the early universe(初期宇宙における大質量BHの質量成長)
Sunmyon Chon (Tohoku Univ.)、
with Takashi Hosokawa (Kyoto Univ.)、
Kazu Omukai (Tohoku Univ.)

Motivation:
Super Massive Black Hole at high-z

2 SMBH with 108-9 M8 at z ~ 7.5 (cosmic age 0.7 Gyr ) Eddington accretion onto BHs…

Observed BHs
30 20

MBH

MBH = Mini exp (t/tE)
where tE  50 Myr

log10 MBH / M⊙

ṀBH

8

Mini= 30 M⊙ at z=30
5=10 M⊙ at z=2010

BH

redshift107⋆86⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆ ⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆ ⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆ ⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆⋆ ⋆⋆ ⋆⋆⋆⋆ ⋆⋆⋆ ⋆⋆⋆⋆6Massiveseed
42

GW150914
00.20.4

Solid : fEdd = 1
Dashed: fEdd = 0.6
0.60.81

cosmic age [Gyr]Not enough time if we start from Mini = 30 M8.

Motivation:
Super Massive Black Hole at high-z

3 SMBH with 108-9 M8 at z ~ 7.5 (cosmic age 0.7 Gyr ) Eddington accretion onto BHs…

Observed BHs
30 20MBH

MBH = Mini exp (t/tE)
where tE  50 Myr

log10 MBH / M⊙ṀBH

8

Mini= 30 M⊙ at z=30
5=10 M⊙ at z=2010BH

redshift
107⋆

86

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Massiveseed
42

GW150914
00.2

0.4

Solid : fEdd = 1
Dashed: fEdd = 0.6
0.6

0.8

1

cosmic age [Gyr]Massive seed scenario is one solution.

3Motivation:
Super Massive Black Hole at high-z

4 SMBH with 108-9 M8 at z ~ 7.5 (cosmic age 0.7 Gyr ) Eddington accretion onto BHs…

Observed BHs
30 20

BHṀBH

MBH

log10 MBH / M⊙108

redshift
10

Mini= 30 M⊙ at z=30
5=10 M⊙ at z=20

87

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⋆⋆⋆⋆ ⋆⋆ ⋆⋆⋆⋆ ⋆⋆⋆ ⋆⋆⋆⋆6Massiveseed4Solid : f = 1
MBH = Mini exp (t/tE)
Dashed: f = 0.6
2GW150914
00.2
0.4
0.6
0.8
1Question where tE  50 Myrcosmic age [Gyr](1) Can we form a massive seed BH?
(2) Does the Eddington accretion continue for cosmic time?
Edd

Edd3

Problem(1) Can we form a massive seed BH?

Direct Collapse model (Brom&Loeb03)
Cloud Collapse-2-22

log < density >20

log DM densit[g/cc]

105 M8 BHs can form at very close to the luminous galaxy.
Accretion phase
60y

Protostar formation-2.54y-20-230.1 pc

2 kpc
-3-40

10 comoving Mpc-24

1 unit-200z

2030 pc

SC+16,SC+182(2) Does the Eddington accretion continue for cosmic time?
5-3.5-2-1.5z-1-0.5

Problem(1) Can we form a massive seed BH?

(2) Does the Eddington accretion continue for cosmic time?
⇒ still, no consensus…

BH Mass [M8]

Di Matteo+12

Latif+181010
1081061086
redshift⇒ seed BHs grow nearly at
the Eddington rate!

4127.5redshift⇒ almost no growth.
6Problem(1) Can we form a massive seed BH?

(2) Does the Eddington accretion continue for cosmic time?
⇒ still, no consensus…

BH Mass [M8]

Di Matteo+12

Latif+181010
108

These calculations do not follow the seed BH formation.
106(put BHs at the center of an arbitrary halo.)
108

64

12

⇒ We will follow
redshiftthe mass growth starting fromredshifttheirformation.
⇒ almost no growth.
⇒ seed BHs grow nearly atthe Eddington rate!

7.5

7Methods
ü We follow the BH growth from their formation.
ü We try to resolve the star formation in the galaxy center.
 Gadget3 (SPH + N-body) Primordial chemistry Star formation
ü PopIII formation (M* = 102 M8)
ü PopII (efficiency=0.05, Salpeter IMF) UV feedback from stars (RSPH by Susa2006)
ü Ionization feedbackü H2 Dissociation
 SN feedback and Metal enrichment
 Metal line cooling

Hirano+2014
Wise & Cen 2012

8

BH growth
We place BH particles
according to the DC model.
pristineclose to luminous galaxy

(black) : BH particle
(white): star particle

Place BH particles

galaxyWe assume the gas accretes onto BHs
at the Bondi rate.
5 comoving kpc

0.01 /cc

1 /cc

100 /cc 9

BH growth
We place BH particles
according to the DC model.
pristineclose to luminous galaxy

(black) : BH particle
(white): star particle

We assume the gas accretes onto BHs
at the Bondi rate.
5 comoving kpc

0.01 /cc

1 /cc

100 /cc10

BH growth
Galaxy center

log10 MBH [M8]

Disruption ofhost halo gas

redshiftEfficient mass growth until BHs reach the galaxy center.
⇒ The host halo gas is abundant around BHs.
The growth gets inefficient once BHs reach the galaxy center.
⇒ BHs are decoupled from the host halo gas
due to the tidal force or ram pressure.

11

BH
BHgrowth
growthGalaxy center

log10 MBH [M8]

Disruption ofhost halo gas

redshiftEfficient mass growth until BHs reach the galaxy center.
⇒ The host halo gas is abundant around BHs.
The growth gets inefficient once BHs reach the galaxy center.
⇒ BHs are decoupled from the host halo gas
due to the tidal force or ram pressure.

12

BH growth
Galaxy center

log10 MBH [M8]

Disruption ofhost halo gas

redshiftEfficient mass growth until BHs reach the galaxy center.
⇒ The host halo gas is abundant around BHs.
The growth gets inefficient once BHs reach the galaxy center.
⇒ BHs are decoupled from the host halo gas
due to the tidal force and ram pressure.

13

log10 density [cm-3]

Why the accretion rate decreases?

According to DC scenario,
BH should have a relative
velocity of halo’s circularvelocity.
(Since they form at the satellite
halo.)

Density is still highRelative velocity between gas and BHs

log10 vrel [km s-1]

A large relative velocity
makes the accretion rate
so small.
(vrel ~ 30 – 100 km s-1)

Gas density around BHs

redshift14

Dynamical friction
BHs migrate toward the galaxy center, as gravitationallyinteracting with the surrounding gas and stars.

It takes 103 Myr to sink toward
the galaxy center.
(cf. cosmic age = 700 Myr at z  7)
⇒ Efficient BH growth might bedifficult in DC scenario.

Beckmann+17
Ostriker1999
15

Alternative scenario
1. Seed BHs form at much closer to the luminousgalaxy.
⇒ initial velocity could be reduced.
⇒ The seed BHs easily sink toward the galaxy center.
⇒ Could be polluted by heavy element⇒ SMS can form (Latif+2016, Tagawa+2019)

2. BH formation by DC is more frequent than wehave expected.
⇒ Their mergers can help the mass growth.

3. Halo mass is too small (109 M8 @ z=14).
⇒ We should focus on rarer peak?

16

Alternative scenario
1. Seed BHs form at much closer to the luminous
galaxy.
2. BH formation by DC ismore frequent thanwe have expected.
⇒ we only allow two
BHs to form, so far.
⇒ There are candidate
sites for BH formation
around the galaxy.
17

Summary
・We have followed the mass evolution of the BHs
starting from their formation.
・BH growth gets inefficient due to the relative velocity
once the BHs reach the galaxy center.
(radiation feedback further reduces the accretion rate.)
・The relative velocity is difficult to decreasesince the tDF is larger than the cosmic time at z〜7.
・ Forming a seed closer to the luminous galaxy
Mergers of seed BHs
are the alternative scenario for the efficient mass growth.

星・銀河からのフィードバック-14-12-10-8

log10 H2 abundance-623

log10 Temperature

4Effects of BH radiation
without BH radiation

with BH radiation⇒ Just after the BH formation, the surrounding gas is heated
up to 104 K.

21

Effects of BH radiation
without BH radiation

with BH radiation⇒ The density structure is smoothed out due to the radiationfrom BHs.
22

Effects of BH radiation⇒ Accretion rate gets
much smaller than theEddington rate.
⇒ Almost no mass growth・-6-10withoutBH radiation

Eddingtonwith BH radiation-14
4

log10 n [cm-3]

Due to the radiation fromthe BHs, the gas density
quickly decreases.

log10 MBH [M8 yr-1]

-2

20-2

191718redshift

161523

Numerical simulation of BH growth

α : boosting factor⇒         

Radiation
SNeHot gas with 105 - 106 K
Fills up the total volume.

If we increase the spatial resolution,
we will observe

the cold and dense  

Numerical simulation of BH growth Springel, Di Matteo, Li … α = 100

Grows at the Eddington rate Smith+18, Latif+18:α=1Almost no growth Dubois+15

:

α =1

(ρ < ρSF)(ρ > ρSF)= (ρ/ρSF)2

Once SN feedback operates,
mass growth gets inefficient.