1. line emission by the first star formation Hiromi Mizusawa(Niigata University) Collaborators Ryoichi Nishi (Niigata University) Kazuyuki Omukai (NAOJ) Formation of the First Generation of Galaxies December 2-5, 2003, Niigata University, Japan

2. Outline  Purpose  Model : the method of calculation  Results : the evolution of T, y( ), luminosity  Detectability of the first stars by SPICA  Summary & Discussion

3. Purpose We estimate the luminosities of lines, which can be characteristics of the first star formation process, and evaluate the detectability of lines. The luminosities of lines for the runaway collapse phase Ripamonti et al (2002) and Kamaya & Silk (2002) However the luminosities of lines for the main accretion phase haven’t been estimated. protostellar cloudprotostar main sequence star main accretion phase we calculate them for both phase. runaway collapse phase １

4. Model The Larson-Penston-type similarity solution, γ ＝ 1.09 (dotted line), reproduces Omukai&Nishi’ result (solid line) well. a good approximation to the actual collapse dynamics. center ---- flat density distribution, runaway collapse envelope ---- leaving the outer part practically unchanged The thermal and chemical evolution of gravitationally collapsing protostellar clouds is investigated by hydrodynamical calculations for spherically symmetric clouds. (Omukai&Nishi 1998) The evolutionary sequences The time interval ２

5. Contracting region and mass become more and more small. Free-fall determined by the local density ３ １． Dynamics ・ The runaway collapse phase The central evolution the free-fall relation modified by pressure gradient β the flat core size ; α the collapse time scale ; β For the Larson-Penston-type similarity solution for γ=1.09,

6. Inner mass shells fall faster than outer mass shells. Free-fall determined by the gravitational force of the protostar ４ ・ The main accretion phase ： the density of free-falling mass shell ： the velocity of free- falling mass shell ： the distance from mass shell to the center Approximation, each mass shell free-fall

7. ２． Energy equation 3. Cooling/Heating processes ： the energy per unit mass ， ： the pressure, ： the temperature ， ： the adiabatic exponent ， ： the mean molecular weight ， : the mass of the hydrogen nucleus ： the cooling rate by line emission ， ： the net cooling rate by continuum emission, ： the net cooling rate by chemical reactions ５

8. --- the population density of in level i --- the spontaneous transition probability --- the energy difference between levels I and j --- the collisional transition rate from level I to level j --- the optical depth averaged over the line --- the escape probability ・ line cooling ６

9. ４． Chemical reactions （ formation processes) （ proce ss) （ three-body reactions ） ・ continuum cooling/heating bound-free absorption of, collision induced absorption Protostar ~ the black body of 6000 K (Omukai & Pala 2003) free-free absorption of, ７ In our calculation, these continuum processes are hardly effective.

10. Initial Conditions The physical condition of fragments (protopstellar clouds) The contraction and fragmentation of primordial, metal-free gas clouds is investigated by some authors. (e.g., Uehara et al. 1996; Nakamura & Umemura 2002 ;Abel et al. 2002; Bromm et al. 2002) ： Jeans mass ： the concentration of the i-th species ： the number density of the hydrogen nucleus We adopt the typical values for the star-forming cores from Bromm et al.(2002). ８

11. Results time The runaway collapse phase ９ time an order Effective cooling by The time evolution of the central temperature three body reactions process The time evolution of the central abundance of ~ ten orders of magnitude

12. time Comparison between runaway collapse phase and main accretion phase For the accretion phase, the evolutionary trajectories of the mass shells of are shown. The main accretion phase The runaway collapse phase 10

13. The evolution of line emission red ： (1,1)→(0,1), green: (1,1)→(0,3), blue ： (0,6)→(0,4), purple ： (0,5)→(0,3) 2.34μm, 2.69μm, 8.27μm, 10.03μm Pick up Pick up : four of the strongest lines rest frame : １１ rovibrational lines rotational lines runaway collapse phase main accretion phase Peak luminosity The central protostar The protostar formation

14. The sources of radiated energy Compressional heating formation heating Until peak luminosity At the same radius, Area indicates the chemical energy unit time, The final stage of collapse phase Three selected time in accretion phase

15. For mid-infrared region ( ), SPICA(ISAS), a large(3.5m),cooled(4.5K) telescope, is the best. (better than JWST and ALMA) :The luminosity distance to z=19 :The peak luminosity The line detection limit of SPICA is about in. more than sources SPICA can observe. 13 Limited by the high background of the zodiacal light (private communication H.Matsuhara). Detectability

16. Summary & Discussion ・ We estimate the line luminosities from the first-generation star formation process. ・ the luminosities of both rovibrational lines and rotational lines become maximum value at the main accretion phase. ・ For the runaway collapse phase, the strongest lines are rotational lines. For the main accretion phase, rovibrational lines overwhelm them. ・ For the peak, rovibratinal lines are stronger than rotational lines. rotational lines ----- low density region such as envelope of the protostellar clouds rovibrational lines ----- high density region such as final stage of star formation process the strong evidence rovibrational lines the strong evidence of the first-generation star formation For observation of the first-generation star, rovibrational lines are important. 14

17.  @ high z, detecting line emission by SPICA is highly improbable.  @ low z, such as, detecting it from Pop III stars by SPICA is maybe possible. Galactic scalelow metallicity Formation of Galactic scale with such low metallicity is maybe excluded in the context of standard cosmology (e.g., Scannapieco,Schneider,& Ferrara 2003). Although, it is necessary to investigate how the mixing of metals occur. If If sources @, SPICA can observe forming first-generation stars. To emit mainly in lines, the metallicity in the pregalactic clouds (Omukai 2000). To exist sources is difficult situation at early universe.