Galaxy Evolution in the Merging Process Hidenori MATSUI 1,2 Takayuki - - PowerPoint PPT Presentation

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Galaxy Evolution in the Merging Process Hidenori MATSUI 1,2 Takayuki - - PowerPoint PPT Presentation

Dec 26, 2023 271 likes •493 views

Galaxy Evolution in the Merging Process Hidenori MATSUI 1,2 Takayuki R SAITOH 3 , Junichiro MAKINO 3 , Keiichi WADA 4 , Kohji TOMISAKA 2 , Eiichiro KOKUBO 2 , Hiroshi DAISAKA 5 , Takashi OKAMOTO 6 ,

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1 Asahikawa National College of Technology 2 National Astronomical Observatory of Japan (NAOJ) 3 Tokyo Institute of Technology 4 University of Kagoshima 5 University of Hitotsubashi 6 University of Tsukuba 7 University of Tokyo

Galaxy Evolution in the Merging Process

銀河衝突合体が引き起こす銀河進化

Takayuki R SAITOH3, Junichiro MAKINO3, Keiichi WADA4, Kohji TOMISAKA2, Eiichiro KOKUBO2, Hiroshi DAISAKA5, Takashi OKAMOTO6, Naoki YOSHIDA7

Project Milkyway

Hidenori MATSUI1,2

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  • Galaxy-Galaxy merging triggers galaxy evolution

dramatically.

  • Active star/star cluster formation (Mengel+2008)
  • Disk galaxies → Elliptical galaxies
  • Evolution of the galactic central region
  • Fueling of gas (Barnes & Hernquist 1996, Kazantizidis

+2005)

  • Coevolution of supermassive black hole and galactic bulge

The role of the Galaxy Merger

Galaxy-Galaxy merging is important process for galaxy evolution. Mengel+ 2008 Marconi & Hunt 2003

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Previous Numerical Simulations

(e.g., Barnes & Hernquist 1996)

  • SPH method
  • Problems
  • limited resolution
  • Interstellar Medium (ISM) model
  • isothermal gas (T=104 K) or radiative cooling (T>104 K)
  • star formation

➡ These simulations cannot reproduce characteristic

structures (shock-induced starburst and star cluster formations) observed in merging galaxies.

➡ The behavior of ISM might be completely different from that

  • f actual merging galaxies.

MSPH ∼ 105−6M⊙ ǫ ≥ 100 pc

Antennae Active star formation

Mihos & Hernquist 1992

dρ∗ dt = C∗ ρgas tdyn

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High Resolution Simulations of Merging Galaxies (Saitoh et al. 2009)

  • Simulation code “ASURA”
  • Tree+GRAPE Nbody/SPH
  • resolution
  • radiative cooling (10 K<T<108 K)
  • heating from Type II supernovae
  • star formation (T<100 K, )

ǫ = 20 pc nH > 100 cm−3 MSPH ∼ 103−4 M⊙

Previous simulations Simulation (Saitoh+2009) star formation star formation

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Results of Saitoh et al. 2009

The behavior of ISM is very different from that

  • f previous simulations.

➡ High resolution simulations with multi-phase ISM model are essential to understand galactic evolution in the merging process.

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Our simulations(Method)

  • ASURA code (Saitoh et al. 2008)
  • particle numbers
  • SPH 510,000, old stars 1,800,000, DM 28,000,000
  • mass/spatial resolutions
  • radiative cooling (10 K < T < 108 K)
  • heating from TypeII supernovae
  • star formation (T<100 K, )
  • using various collision geometries

nH > 100 cm−3 MSPH = 7 × 103 M⊙ ǫ = 5, 20 pc

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Simulation Models

Dark halo(Dark matter) Disk(gas＋old stars) Disk(gas＋old stars) exponential disk

Mgas ∼ 109 M⊙

MDM ∼ 1011 M⊙

Mdisk ∼ 1010M⊙

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Collision Geometries

Orbit：Parabolic

Rperi

Rperi (kpc) i1 ω1 i2 ω2 tilt/tilt 7.5

  • 109
  • 30

71

  • 30

x y i z ω

Inclination of disks

  • rbital plane
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Results

  • 1. Formation of Hypermassive Star Clusters
  • 2. Origin of Multiple Nuclei
  • 3. Mass supply to the galactic central region
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Results

  • 1. Formation of Hypermassive Star Clusters
  • 2. Origin of Multiple Nuclei
  • 3. Mass supply to the galactic central region
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Formation of Hypermassive Star Clusters

  • Mass of star clusters

1. 2. 3.

1.7 × 108 M⊙ 1.3 × 108 M⊙ 6.9 × 107 M⊙ Distribution of newly formed stars

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Results

  • 1. Formation of Hypermassive Star Clusters
  • 2. Origin of Multiple Nuclei
  • 3. Mass supply to the galactic central region
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ULIRGs with multiple nuclei @ z~0.1 (Borne+2000, Cui+2001)

Borne et al. 2000

  • ULIRGs
  • L(8μm-1000μm) >

Absolute Magnitude of core MI < -17 (Cui et al. 2001)

  • Observation of ULIRGs@z~0.1 by HST I-band

20% (<80%) of the samples have multiple nuclei.

1012L⊙

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Our simulation data + PEAGSE (I-band)

10 kpc 950 Myr

  • Absolute Magnitude (I-band）
  • 1. -17.6
  • 2. -17.2
  • 3. -16.4

1 2 3 Galaxies with multiple nuclei are explainable in a single major merger.

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Results

  • 1. Formation of Hypermassive Star Clusters
  • 2. Origin of Multiple Nuclei
  • 3. Mass supply to the galactic central region
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Mass Supply to Galactic Central Region

ε=20 pc Mass evolution (<100 pc)

second encounter

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Density Profile

DM+Baryon Kazantzidis+2005 Matsui+ in prep

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Summary

  • We have performed high resolution simulations of

merging galaxies.

  • Hypermassive star clusters form in the merging

process.

  • Galaxies with multiple nuclei are explainable in a

single major merger.

  • Mass supply (< 100 pc) takes place in merging

process.