Star formation in forming galactic disks under UV field by RHD simulation Hajime Susa Department of Physics, Konan university, Kobe, Japan Susa ApJ 684, 226, 2008
Jan 06, 2016
Star formation in forming galactic disks under UV field
by RHD simulation
Hajime Susa Department of Physics, Konan university,
Kobe, Japan
Susa ApJ 684, 226, 2008
Ultraviolet radiation field ( >13.6eV )
Physical processes heating : T ~ 104 K
ionization+dissociation
background I21= 0.1 - 1 @ z= 2 – 5
I21=0.01- 0.001 @ z=0
Keep the gas in the proto-galaxies hot ( ~ 104 K).
Feedback on star formation?
Around forming gals I21 ~ 1-100 (star formation)
I21 ~ 100(AGN @10kpc)
Formation of dwarf gals.
M=1e8MsunZc ~ 5zreion ~ 7
Susa & Umemura 2004ab
M < 1e8 Msun→ SF shutdown
Aim of this work
• Assess the effects of UV on massive DM halos with Tvir > 104K. Star formation in these systems are regulated or not ?
As a first step, we investigate the stability of gas disks in massive halos under UV field, utilizing radiation hydrodynamics simulations.
RSPH code
• Parallel BH Tree• SPH• Domain decomposition : ORB• RT solver (Ray-Tracing)• Implicit solver for reactions and energy
equation• H2• On-the-Spot approximation (Case B recom.)• Multiple sources ( ~ < 10 )• Any Spectrum
Susa 2006 (http://ads.nao.ac.jp/abs/2006PASJ...58..445S)
The model
1 2 1 2100 0 3 5-1kms kpc, kpc, .v v a a Same as Wada & Norman 2007except rotation velocity
21
100
0 05 0 1 0 3
0 1
3
300
110
H
M
I
R
T
m M
-3ini
disk
min
sph
pc
pc
or
kpc
K
=
: . , . , . ¤
¤Uniform disk with slight perturbations
radiation
radiation
Resolution
Mass resolution :
Maximally resolved density: (MJ~ Mres)
42 1 1 10N m M nei SPH . ¤
3
2
3 5 1235
4 2 2
kTn
m Gm m N
-3BH,res
p p SPH nei
cmmin
Gravity Softening: ( ~ minimal SPH softening)
1 3
313
2 4
N mmn
nei SPH
p H,res
pc
/
Bate & Burkert 1997
montage: I21=0
Disks in all modes (A 、 B 、 C) are unstable → fragmentation & star formation
21 -2H 1 3 10 cmN . 20 -2
H 6 6 10 cmN . 21 -2H 4 0 10 cmN .
Toomre Q and the tmperature PDF(I21=0)
Unstable
Stable
AB
C
min@Q T T
Tmin
scQG
Tmin Tmin
diskR
montage: I21=1
C: still unstable → fragmentation & star formation
A, B : stable → star formation is strongly suppressed.
21 -2H 1 3 10 cmN . 20 -2
H 6 6 10 cmN . 21 -2H 4 0 10 cmN .
Density PDFs
No dense components
21 0I
21 1I
Distribution along z-axis
density
temperature
HI Significant self-shielding effect
Temperature PDFs0 06Mass fraction ( ) per / log .totalM M T
Ar, Br : unshielded →Hot component dominates→ large Q → stable
Cr : shielded →Cold component dominates→ small Q → unstable
Threshold column density for self-shielding
Numerical results : NH,sh ~ 1-4×1021cm-2
Can UV photons suppress the SF in disks hosted by massive dark halos?
Hierarchical GF
Dynamical effects of merging (shock induced SF etc.) Inhomogeneous distribution of heavy elements Radiation from forming stars in building blocks, AGN
Fresh Gas accretion Fresh Gas accretion
On going………
Analytical model of Cosmological disks (1/2)
• Dark halos parameterized by (z c, M, λ )
• Assume half of the baryons settle onto the galactic disk
• Keplar rotation & hydrostatic equilibrium in z-direction
• NH, disk > NH,sh ?• Q >1 ?
Analytical model of Cosmological disks ( 2/2 )
H ,disk H ,shN N410 K = 1Q@
210 K = 1Q@
Unshielded& stable
Unshielded& stable
Bimordality of galaxies
Ste
llar
ag
eo
ld
new
Resent SF for galaxies with
Mstar < 1010Msun
(Kauffman, G. et al, MNRAS, 341, 54, 2003)
Some process to delay the SF in less massive galaxies is required.
Photoheating
Summary• We perform radiation hydrodynamics
simulations on the fragmentation of galactic disks under the ultraviolet radiation background.
• We find that ultraviolet radiation field strongly suppress the star formation in the disks in case the photoheating is not shielded enough.
• In our simulations, we find a threshold column density of the disk ( ~ 1021(I21/1)cm-2) above which the fragmentation is not suppressed.
• Presence of such critical threshold would be one of the reason for the so-called down-sizing problem in nearby galaxies.
Tours Symposium 2009
• Nov. 16-20 @ Tours, France• Nuclear Physics, High energy
astroparticle physics, Astrophysics• Astrophysics: “First & Second generation stars”
SOC Ferrara, Schneider, Umemura, Omukai, Tominaga, Susa