1. The Inter-Galactic Populations and Unbound Dark Matter Ing-Guey Jiang and Yu-Ting Wu National Tsing-Hua University Taiwan

2. Outline –Introduction –The Model –The Results –Conclusions and Implications

3. Introduction Zwicky (1951) –found diffuse light between galaxies –imply luminous stars exist between galaxies many inter-galactic objects are observed –red giant, planetary nebulae, supernovae (Gerhard et al. 2005, Gal-Yam et al. 2003) Virgo cluster –Durrell et al. (2002): intra-cluster stars could contribute 10%~20% of the total luminosity

4. Introduction one of the scenarios- The Mergers The galactic mergers Antennae Galaxies J. Hibbard

5. The Model Stanghellini et al. (2006) –dry mergers of spherical elliptical galaxies –head-on collisions –neglect the dark halo –5% ~ 20% of the total mass become unbound stars. Our work: N-body simulation disc galaxy - disc galaxy –disc galaxy: stellar disc and dark halo

6. The Model The galaxy : the stellar disc and dark halo Density profiles (Hernquist 1993): –disc: –halo: Parameters: HaloDisc M h =32.48×10 10 M ⊙ M d =5.6×10 10 M ⊙ r c =3.5 kpch=3.5 kpc r t =35.0 kpcz 0 =0.7 kpc N h =58,000N d =10,000

7. The parabolic mergers –relative velocity=147.8 km/s The hyperbolic mergers –relative velocity=273.1 km/s The separation of the galaxies is 300 kpc (1) (2) (3) (4) (5) (6)

8. A Disc-Halo System

9. Virial Ratio of a Merging Event

10. Model P1: stellar part

11. Model P1: Dark Matter

12. Six Parabolic Mergers

13. Results the parabolic merger the hyperbolic merger

14. Evolution of Unbound Fractions

15. Conclusions and Implications head-on merging events make a considerable fraction of dark matter become unbound only a tiny fraction of the stellar part become gravitationally unbound To explain the observed intergalactic populations, multiple mergers and tidal interactions play roles Some intergalactic populations might be bounded and trapped by dark matter. This implies a definition problem. Applications: observable population shall give hints on velocity and space distributions of dark matter Thus, there is a chance to trace Unbound Dark Matter

16. The End

17. Computing Facilities GADGET (Springel et al., 2001) –GAlaxies with Dark matter and Gas intEracT –Parallel Version 1.1 –National Center for High-Performance Computing

18. The Units G=43007.1 [L]=1 kpc [M]=10 10 M ⊙ [T]=9.8 × 10 8 years