2007. 10. 31

Activities and Collaborations

Group Members
Faculty (3)Graduate Students (15)Masayuki Umemura (Professor)
Hiroyuki Hirashita (Assistant Professor)
Kohji Yoshikawa (Assistant Professor)

Ikko Shimizu (D3)
Kenji Hasegawa (D3)
Seiji Yasuda (D2)
Rogel Mari D. Sese (D2)
Chizuru Akizuki (D1)
Masaru Sakuma (D1)
Daisuke Sato (D1)
Hidenobu Yajima (D1)
Takayuki Koizumi (M2)
Mayumi Chiba (M2)
Masao Doi (M2)
Tomohiro Ichikawa (M1)
Makoto Takenaka (M1)
Ryota Narita (M1)
Takayuki Wada (M1)

Postdoctral Fellows (4)Yoshiaki Kato
Tamon Suwa
Takuya Akahori
Yasuyuki Watabe (in Italy)

Undergraduate Students (4)Yuki Kubota (B4)
Yuko Kurotori (B4)
Keiki Saitoh (B4)Masahito Matsumine (B4)History
1993: Masayuki Umemura from NAOJ
1994: Taishi Nakamoto from NAOJ (moved to TiTech, 2006)
Joined CP-PACS Project
Collaboration with particle physicists and computer scientists
Started 3D Radiative Transfer
1997:“Development of Next Generation Massive Parallel Computer Project”
started (1997 - 2001)
Collaboration with particle physicists and computer scientists
HMCS (Heterogeneous Multi-computer System) constructedStarted 3D Radiation Hydrodynamics
2000:International Conference, The Physics of Galaxy Formation
2004:
Center for Computational Sciences set up
FIRST Project started
Collaboration with computer scientists
2005: Hiroyuki Hirashita from Nagoya U.
2007: Kohji Yoshikawa from Tokyo U.

Radiative Transfer
with CP-PACS

1 ∂I ν+ n ⋅ ∇I ν = χν (S ν − I ν )c ∂t
Freedom: 3D in space, 2D in directions, 1D in frequency = 6D problem
3D Radiative Transfer with CP-PACS
N3＝1283, Nθ＝Nφ＝128, Nν＝6Total memory: 23N3＋3N2NθNφNν ＝ 38.7GB
Total operations: f NiterN3NθNφNν＝1.14 Tflops・hr ( f ≈200, Niter=100)

Short Characteristics method(Kunasz&Auer1988)
Transfer is solved along a short ray across each grid
• Simple coding• Operations are fewer than long char.
～Nx Ny Nz ・Nθ Nϕ Nν

• Interpolation between adjacent grids
causes numerical diffusion.

3D Radiative Transfer with Scattering
Nakamoto, Umemura, Susa 2001
I21=0.1

0.3Gyr

0.5GyrReionization History in an Inhomogeneous Universe

0.7Gyr1GyrPAVEMENT - Parallel I/O & Parallel VR“Development of Next Generation Massive Parallel Computer Project”

QSO

ART(Authentic Radiative Transfer)
Transfer is solved along a long ray across the domain• Physical quantities are interpolated
at each grid
• A bit complex coding• No numerical diffusion(accuracy equivalent to long char.)• Operations (same as short char.)～Nx Ny Nz ・Nθ Nϕ NνTEST OF BEAMING
Short Char.

ART

Cosmological Radiative Transfer Codes Comparison Project I:
The Static Density Field Tests
2006, MNRAS, 371, 1057
Ilian T. Iliev, Benedetta Ciardi, Marcelo A. Alvarez, Antonella Maselli, Andrea Ferrara, Nickolay Y.
Gnedin, Garrelt Mellema, Taishi Nakamoto, Michael L. Norman, Alexei O. Razoumov, Erik-Jan
Rijkhorst, Jelle Ritzerveld, Paul R. Shapiro, Hajime Susa, Masayuki Umemura, Daniel J. WhalenART

Direct Photons + Diffuse Photons
Hiroi, Umemura, Nakamoto, in prep

XHI

XHeI

XHeII

Pop III stars
100 M~
Black Body
2Mpc

BH accretions
104 M~
Power-law
9Mpc

Reionization at z=10

Galaxy Formation with UV Background
Three Elements for Galaxy Formation
CDM Fluctuations
Random Gaussian Density Fields
Cooling Diagram (Rees & Ostriker 1977)+ρgasd ρ*= c*star formation
dttff+Self-Shielding
No stars form unless baryonic matter is self-shielded from UVB !

Formation of Dwarf Galaxies during the Cosmic Reionization
Susa & Umemura 2004, ApJ, 600,1
TREE-SPH + Radiation Transfer + Non-equilibrium Chemistry
NDM=NSPH=131072

M vir = 6 × 108M~
zc = 7.6
UVSource

Final Stellar Fraction
M vir = 108−9M~
20 km s-1 d vcirc d 40 km s-1
Dwarf galaxies do form
even during reionization

almost regardlessof c* !
Mvir = 109 M~

c*=1, 0.1, 0.01

c*=0.01,0.1,1Mvir = 108 M~
c*=0.01,0.1,1zc

fstar 7 ×10−2 (1 + zc ) + b(M ) b(109 M~) = 0.35, b(108 M~) = 0.15

By Earth Simulator & CP-PACS
CP-PACS

10243 Hydrodynamic Calaculations
80,000,000 SN explosions

Mori and Umemura, 2006,
Nature, 440, 644

Cover page of Nature(March 30, 2006)

Evolution ofGas Density
Total Mass:1011 M~
Gas Mass: 1.3×1010 M~# of Subunits: 20
Box Size: 134 kpc
Grid Points: 10243

0.3Gyr

0.5Gyr1GyrLyα blobMatsuda et al. 2004

Simulation

Comparison of the simulation with observation
Left: Projected distribution of Lyα emission derived by numerical results.
Right upper: Lyα image of the LABs observed by Matsuda et al. (2004)
Right lower: Simulation result smoothed with a Gaussian kernel with a FWHM of 1.0”.

Subsequent Dynamical Evolution with N-body
Simulation with Million Particles
The virializaion of the total system isalmost completed 3 Gyrs.
The resultant system at
13 Gyrs (redshift z=0) :Stellar mass:
M*=1.1×1010 M⊙
Central velocity dispersion:
V0=133 km s-1
Effective radius: Re=3.97 kpc
B-band mag.: MB= -17.2
V-band mag.: MV= -18.0
Color:
U-V=1.15
V-K=2.85
These values are consistent withthe properties of the present-day
less-massive elliptical galaxies.

Pop III Binary Formation
Saigo, Matsumoto, Umemura, 2004, ApJL, 615, L65

Present-day Stars
over 50% are binaries !
Pop III Stars
massive binaries

Level 3

3D Simulation with nested grids

Level 2

3D nested grid with 20 Levels
Δx = L /128×219 = 8.3×10-5AU
Level 1

Binary Formation
Low rotation caseβ ≡centrifugal force= 0.1
pressure force

rotationally-supported disk

mass accretion
１AU

Trot= 0.245
W< 0.27
ring instability

binary formation

High rotation caserotationally-supporteddiskβ ≡centrifugal force=1
pressure force

mass accretion

Trot= 0.327
W> 0.27

no ringbar instability(single star)Survival of BH Accretion Disk from SN
Sato & Umemura 2007
MSN=100M~ , MBH=1000M~
ESN =30Edisk

70% of accretion disk is left

Future Plan
1. Intensive Simulations with FIRST simulator
Operation of FIRST continues after 2007 as well

2. Collaborations with Other Divisions• with Division of High Performance Computing Systems
Multiple Architecture Seamless System (MASS)- Extension of FIRST simulator (with SSE, Graphic board, etc.)• with Division of Materials and Life Sciences
ab initio (DFT) calculations of hydrogen molecule reactions(H+H+H ↔ H2+H) -- First star formation⇒ Quantum Astrophysics
3. “Computational Observatory” ProjectComputational Observatory Project
Multi-wavelength Data
Telescope

Data Processing, Grid
Database

Detector

AstronomicalObservatory

Data Analysis

VirtualObservatory

ComputationalObservatory
Software
Radiation-Magneto-HydrodynamicScheme
Multi-wavelength Simulation

HardwareMulti-Architecture Seamless System(MASS)

Thank youComputational Science Colloquium
15:30, Nov 1, 2007
Workshop Room

Activities at the Laboratory for
Computational Astrophysics, UCSD
Prof. Michael L. Norman
University of California, San Diego