Star formation triggered by first supernovae
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Star Formation Triggered By First Supernovae. Fumitaka Nakamura (Niigata Univ.). 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?.

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Star Formation Triggered By First Supernovae

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Star formation triggered by first supernovae

Star Formation Triggered By First Supernovae

Fumitaka Nakamura (Niigata Univ.)


Questions

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)


What is the typical mass of first stars

HII region

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., Tsuribe’s 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.


Positive feedback of uv radiation

(Nakamura & Umemura 2002)

Formation of HD molecules

Threshold H2 abundance

xH2 > 3 x 10-3

(Nakamura & Umemura 2002)

Positive feedback of UV radiation

  • Enhanced H2 formation

HD cooling is more dominant for T < 100 ~ 200 K


Thermal property of primordial gas for hd controlled case

g ~ 5/3

g ~ 1

Fragmentation !

For HD dominant clouds, EOS is almost isothermal.

Thus, there is a possibility for the fragments to break up into multiple cores.

Fragment mass ~ 10-40 M8.

Thermal Property of Primordial Gas for HD Controlled Case

  • H2 controlled collapse

  • HD controlled collapse

sphere

g ~ 1.1

Temperature

cylinder

density

Machida et al. (in prep.)

Omukai 2000


Summary part 1 typical mass of first generation stars

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 10~40 M8.

  • Massive binary stars may be common product.

Effect of HD cooling !

Fragmentation !

HD cooling


Can first supernovae trigger subsequent star formation

SNR

Shock-cloud interaction

(e.g., Shigeyama & Tsujimoto 1998)

Fragmentation of cooling shells

Compression of cloud cores

Complete mixing

No mixing

Cloud destruction?

Induced SF?

Induced star formation?

Can First Supernovae Trigger Subsequent Star Formation?

Supernovae of first stars


Evolution of snr

Step 2: 2D hydrodynamic simulation

Then, we follow fragmentation of the cooling shell with the thin-disk approximation.

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


Evolution of snr step 1

Evolution of SNR: Step 1

Machida et al. (in prep.)

Radius and expansion velocity

Evolution of density

Evolution of temperature


Formation of self gravitating shells

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.


Fragmentation of cooling shells step 2

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.)


Fragmentation of cooling shells

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.


Fragmentation condition of snr

Fragmentation Condition of SNR

  • The shell should be self-gravitating before blow out.

  • Expansion velocity should be larger than the sound speed.


Summary part2 star formation triggered by first supernovae

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-massmetal-free stars

Metal cooling

Formation of massivemetal-free stars

~10-40M8.

Similar to present-day SF

~1M8.


Effect of mixing

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.


Shock cloud interaction

Shock-Cloud Interaction

The density can become greater than 104 cm-3 for nearly isothermal case.

Shock can trigger gravitational collapse before KH instability grows significantly.

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.


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