1. 1 Landau Damping of Baryonic Structure Formation in the Post Reionization Epoch Feng-Yin Chang Arxiv:1006.5777 Leung Center for Cosmology and Particle Astrophysics (LeCosPA), National Taiwan University COSMO/CosPA 2010, Tokyo

2. 2 Reionization plasmaneutral gasplasma ( from WMAP7) from QSO spectrum Becker,et al (2001) Larson, et al (2010) Bolton, et al (2010)

3. 3 Previous Studies Effects of reionization on intergalactic medium (IGM) and low-mass galaxies were studied by many researches. In 1986, Rees and Ikeuchi independently pointed out the increasing of gas temperature during reionization could suppress the formation of small galaxies with mass less then Jeans mass. Gnedin (2000) proposed the filtering scale as the characteristic scale for the baryonic fluctuation, instead of Jeans scale, for linear and nonlinear regimes. Chen and Lai (2007) first consider the plasma collective effects on the baryonic structure formation, but their calculation is incomplete. P,Chen& KC La,i PRL(2007) Gnedin, ApJ (2000) Rees, MNRAS (1986) Ikeuchi AP&SS(2986)

4. 4 Why Plasma Effects? Three Plasma Criteria: Plasma collective effects: plasma wave, Landau damping, instabilities….

5. 5 Plasma Waves

6. 6 Linear Fluid Equations ionized gases plasma For mean molecular weight

7. 7 Landau Damping F.Chen 0.4 of one oscillation period the ion acoustic wave would be Landau-damped to e-fold of its initial amplitude. The nonlinear empirical formula

8. 8 Solution of Baryon Fluctuation For simplicity, damping where oscillation part const.

9. 9 Results Ionized gas ionized gas plasma w LD plasma w/o LD For Gnedin &Hui, MNRAS(1998) The suppression of modes with intermediate and high k due to Landau damping gives rise to a correction of k f F.Y.Chang, P.Chen, ArXiv:,1006.5777

10. 10 Modified Filtering Scale F.Y.Chang, P.Chen, ArXiv:,1006.5777

11. 11 ionized gas plasma Results The two characteristic wavenumbers for plasma and ionized gas deviate larger in high redshift.

12. 12 Landau Damping on Early Evolution The small-scale baryon acoustic oscillations in early post-reionization epoch can help distinguish the models plasma ionized gas

13. 13 Recent measurements We are here Tegmark et. al, 2002 We seek for a cosmological survey for small-scale structure formation.

14. 14 Summary The plasma collective effects on baryonic structure formation in the post-reionization is considered. Two major plasma influences: sound speed and Landau damping. The ion acoustic modes were rapidly smoothed out due to the Landau damping. The Landau damped spectrum should be characterized by a modified filtering scale. Measurement of small-scale baryonic oscillation is essential to learn the nature of the cosmic structure formation.