Star Formation Triggered By First Supernovae

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Star Formation Triggered By First Supernovae

• Fumitaka Nakamura (Niigata Univ.)

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Questions

• What is the typical mass of the first stars?

• Can primordial cloud cores break up into multiple
  fragments?
• Binary formation?

• Can first supernovae trigger subsequent star
  formation?

• What is the typical mass of the stars formed by
  shock compression?
• low mass star formation? (e.g., HE0107-5240)

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What is the typical mass of first stars?

• Typical mass of fragments 100M8
• No fragmentation for the polytrope gas with g
  1.1.
• (e.g., Tsuribes talk)

Size of HII region 100 pc Free-fall time of
fragments 106yr ? Positive feedback of UV
radiation ? Enhanced H2 formation
30 pc
(Bromm, Coppi, Larson 1999)

• If a truly first star is massive, it emits strong
  UV radiation, which should affect subsequent
  evolution of other prestellar fragments.

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Positive feedback of UV radiation

• Enhanced H2 formation

HD cooling is more dominant for T lt 100 200 K
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Thermal Property of Primordial Gas for HD
Controlled Case

• H2 controlled collapse

• HD controlled collapse

g 1.1
sphere
Temperature
cylinder
density
Machida et al. (in prep.)
Omukai 2000
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Summary part 1 typical mass of first generation
stars

• Truly first stars may be very massive as 100 M8.
• But, many first generation stars may have masses
  of 1040 M8.
• Massive binary stars may be common product.

Effect of HD cooling !
Fragmentation !
HD cooling
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Can First Supernovae Trigger Subsequent Star
Formation?
Supernovae of first stars
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Evolution of SNR
cooling
adiabatic
1. Free expansion
2. Sedov-Taylor
3. Pressure-driven expansion
Step 1 1D calculation We follow the evolution of
the SNR shell with the thin-shell approximation.
Dynamical evolution analytic model Thermal
evolution radiative cooling time-dependent
chemical evolution
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Evolution of SNR Step 1
Machida et al. (in prep.)
Radius and expansion velocity
Evolution of density
Evolution of temperature
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Formation of Self-Gravitating Shells

• The cooling shell is expected to become
  self-gravitating by the time 106 - 107 yr.

Formation of self-gravitating Shell ? Tff Tdyn
Tff
Tcool
Tdyn
Texp
Texp is sufficiently longer than Tff and Tdyn at
the final stage.
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Fragmentation of Cooling Shells Step 2

• Fragmentation of a self-gravitating sheet

• Thin-disk approximation
• isothermal EOS
• Power law velocity fluctuations
• 2D hydro simulation

Nakamura Li (in prep.)
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Fragmentation of Cooling Shells

• Mass fraction of dense regions reaches 0.7.
• ? star formation efficiency may be high.

M Mach number of the velocity perturbations

• Dense cores are rotating very rapidly.

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Fragmentation Condition of SNR

• The shell should be self-gravitating before blow
  out.
• Expansion velocity should be larger than the
  sound speed.

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Summary part2 Star Formation Triggered by First
Supernovae
Supernovae of first stars
SNR
Shock-cloud interaction
Fragmentation of cooling shells
Compression of cloud cores
Complete mixing
No mixing
1M8.
Induced SF
Z 10-3Z8
HD cooling
Formation of low-mass metal-free stars
Metal cooling
Formation of massive metal-free stars
10-40M8.
Similar to present-day SF
1M8.
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Effect of Mixing
The temperature goes down to 20-40 K.

• Dense cores are rotating very rapidly.
• ? binary formation
• Dense cores may fragment into small cores with
  masses of 1 M8.
• The efficiency of star formation may be high.

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Shock-Cloud Interaction

• Shock can trigger gravitational collapse before
  KH instability grows significantly.

The density can become greater than 104 cm-3 for
nearly isothermal case.
Polytrope gas, 2D axisymmetric, no self-gravity
Nakamura, McKee, Klein (in prep.)
Fragmentation into 1M8 cores is expected due to
efficient H2 cooling by three-body reaction.