# Presentation: 363831

## High Resolution P3M-GRAPE-SPH Simulations of PopIII Star Formation 

- High Resolution P3M-GRAPE-SPH Simulations of PopIII Star Formation

- Tamon SUWA1†, Masayuki UMEMURA1, Daisuke SATO1, Hajime SUSA2, & FIRST Project Team

- 1. Introduction

- Abstract
- In order to derive the mass distribution of Population III stars, we perform high-resolution cosmological hydrodynamic simulations in a standard Lambda-CDM universe. We use a Particle-Particle-Particle-Mesh (P3M) scheme for gravity force calculations, where the PP part is calculated by GRAPE (special purpose board for gravity calculation). The baryon component is treated by Smoothed Particle Hydrodynamics (SPH) method. The simulations are performed on a large PC-cluster system named FIRST with the peak speed of 36Tflops at the University of Tsukuba. In 64-node parallel computation on this cluster, we employ about 108 of dark matter and SPH particles, respectively. With this large number of particles, sub-solar mass resolution for baryon particles can be achieved all over the simulation box. Therefore, we can resolve small scale density fluctuations, which play important role in the formation of intermediate-mass Pop III stars formation.
- We found that the densest cloud in our simulation contract into elongated shape, and finally fragmentation occur.

- 2. Method

- 4.Summary

- 3.Results

**Initial condition**

- Cosmological density perturbation at z=15 is generated by truncated-Zel’dvich approx.
- Cosmological parameters of WMAP 3-year data is accepted
**(********0****,********b****, h)=(0.24, 0.04, 0.73)**
- Simulation box size: 100kpc (comoving)
- 2×107 particles (for DM and SPH, respectively)
- Mass resolution: 0.3MO for SPH particle
-                             1.8MO for DM particle

- 1 University of Tsukuba
- 2 Konan Universiy
- †tamon@ccs.tsukuba.ac.jp

**Mass of the first stars**

**Massive stars (>100M****O****)**

**Isolation or Fragmentation?**

**Less massive stars (~1M****O****)**

- Many of authors have suggested that the first stars are massive
- ex)
- Bromm, Coppi, & Larson (2002)
-  1000MO clumps are formed in their simulation

- Yoshida et al. (2006)
- They estimate the MZAMS~100MO

- Nakamura & Umemura (2001)
- Suggested Bimodal IMF

- O’Shea & Norman (2007)
- They perform 12 AMR simulations and suggest that PopIII stars always form in isolation.
- Yoshida et al. (2006) also suggest isolated PopIII star formation

**Isolated star formation**

**Evolution of the densest peak**

- Initial condition at z=15
- We focus on evolution of the densest peak in the box.

- kpc (comoving)

- We have performed cosmological P3MSPH-GRAPE
- Simulation box size: 100kpc (comoving)
- 0.3MO mass resolution for baryon particles
- The densest peak in our simulation contract asymmetrically
- We showed **fragmentation** of density peak
- The fragmented peaks also show elongation

**Fragmentation!**

**Nishi et al. (1998, PTP, 100, 881)**

**Fragmentation of filament**

- O’Shea & Norman (2007)

- Nakamura & Umemura (2001) showed that if a filament is initially as dense as nc>105cm-3, the fragment mass is lowered down to 1MO.

**Stage 1: Nonlinear Growth **

**Stage 2: Asymmetric Runaway**

**Stage 3: Fragmentation**

**Elongated shape**

- Abel, Bryan, & Norman (2002)
- In their simulation, isolated and massive star is suggested

**Density profile of the peaks**

- [cm-3]

**Stage 2: Asymmetric Runaway**

**Stage 3: Fragmentation**

- green: along x-axis
- red: along y-axis

- Density profile

- [cm-3]

- [kpc]
- (comoving)

- green: along x-axis (peak1)
- red: along y-axis (peak1)
- blue: along x-axis (peak2)
- pink: along y-axis (peak2)

- red: peak1
- blue: peak2

- Density profile

- Mass profile

- peak1

- peak2

- Mass profile

- [kpc]
- (comoving)

- [MO]

**We investigate possibility of the fragmentation in primordial dense core, using uniformly high-resolution cosmological simulations.**