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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? 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? Typical mass of fragments ~ 100M8 No fragmentation for the polytrope gas with g = 1.1. (e.g., Tsuribe’s talk) HII region 30 pc Size of HII region ~ 100 pc Free-fall time of fragments ~ 106yr ↓ Positive feedback of UV radiation ↓ Enhanced H2 formation (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 Enhanced H2 formation H e H h (Nakamura & Umemura 2002) H H H 2 e Formation of HD molecules D H 2 HD H D H 2 HD H Threshold H2 abundance xH2 > 3 x 10-3 HD H2 LiH (Nakamura & Umemura 2002) HD cooling is more dominant for T < 100 ~ 200 K Thermal Property of Primordial Gas for HD Controlled Case Temperature HD controlled collapse g ~ 5/3 sphere H2 controlled collapse g ~ 1.1 cylinder g~1 density Machida et al. (in prep.) Fragmentation ! Omukai 2000 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. 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. Effect of HD cooling ! Massive binary stars may be common product. Fragmentation ! HD cooling Can First Supernovae Trigger Subsequent Star Formation? Supernovae of first stars SNR Shock-cloud interaction (e.g., Shigeyama & Tsujimoto 1998) Fragmentation of cooling shells Complete mixing Compression of cloud cores No mixing Cloud destruction? Induced SF? Induced star formation? Evolution of SNR adiabatic 1. Free expansion 2. Sedov-Taylor cooling 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 Step 2: 2D hydrodynamic simulation Then, we follow fragmentation of the cooling shell with the thin-disk approximation. Evolution of SNR: Step 1 Radius and expansion velocity Machida et al. (in prep.) Evolution of density Evolution of temperature Formation of Self-Gravitating Shells The cooling shell is expected to become self-gravitating by the time 106 - 107 yr. Tff Tcool Tdyn Formation of self-gravitating Shell ↓ Tff = Tdyn Texp Texp is sufficiently longer than Tff and Tdyn at the final stage. 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 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 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 Supernovae of first stars SNR Shock-cloud interaction Fragmentation of cooling shells Complete mixing No mixing Z ~ 10-3Z8 HD cooling Metal cooling Compression of cloud cores Induced SF Formation of low-mass metal-free stars Formation of massive metal-free stars Similar to present-day SF ~1M8. ~1M8. ~10-40M8. 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 can trigger gravitational collapse before KH instability grows significantly. The density can become greater Polytrope gas, 2D axisymmetric, no self-gravity than 104 cm-3 for nearly isothermal case. Nakamura, McKee, & Klein (in prep.) Fragmentation into 1M8 cores is expected due to efficient H2 cooling by three-body reaction.