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Simulating environmental effects: Stripping, interaction, & feedback.

Simulating environmental effects: Stripping, interaction, & feedback. Kenji Bekki (University of New South Wales, Australia). Today’s topics. Stripping of galactic halo gas in different environments. Galaxy interaction. Tidal fields of groups/clusters. Galaxy mergers in small/compact group.

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Simulating environmental effects: Stripping, interaction, & feedback.

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  1. Simulating environmental effects: Stripping, interaction, & feedback. Kenji Bekki (University of New South Wales, Australia).

  2. Today’s topics • Stripping of galactic halo gas in different environments. • Galaxy interaction. • Tidal fields of groups/clusters. • Galaxy mergers in small/compact group. • Time-changing cluster tidal fields and IGM during the growth of groups/clusters via hierarchical merging.

  3. Structure of the talk Simulations • Simulations of environmental effects (with animations). • Implication of the results (which would help observers to interpret their results). Comparison Observations (Hickson compact group 40) [Subaru image]

  4. (I) Halo gas stripping. • The stripping of galactic halo gas due to hydro-dynamical interaction between galactic gaseous halos and IGM of their host environments (e.g., Larson et al. 1980). Gas disk Halo gas IGM A cluster of galaxies

  5. Ram pressure (Pram) vs restoring force of halo and disk gas (Fhalo and Fdisk) Cluster-centric distance (kpc) 200kpc Mcl=1014Msunrs=260kpc (NFW), Fb=0.14. 50kpc Pram=rIGM*v2 (sim. units) Fdisk Fhalo For MW-type disk galaxy Time (Bekki 2009)

  6. Simulating halo gas stripping. (DM halo + bulge + disk stars/gas + halo gas+SF) Animation Halo gas Disk gas Hot gas V=500 km/s T=107 K (Mcl=1014 Msun) Md=6*1010Msun,vc=220 km/s,B/D=0.2 (Bekki 2009)

  7. GRAPE7-SPH simulation: Halo gas stripping (Bekki et al 2002; 2009).

  8. Efficiency of gas stripping in different environments. Mg Time Fstrip=0.65 (Halo) • (V=500 km/s, rIGM=4*10-3 atoms/cm3, • T=107 K [Mcl=1014 Msun ], • R~200kpc) (Bekki 2009)

  9. Cluster: Fstrip=0.65 (Halo) (V=500 km/s, T=107 K [Mcl=1014 Msun ]) Group: Fstrip=0.38 (Halo) (V=200 km/s, T=3*106 K [Mcl=1013 Msun ]) (Bekki 2009)

  10. Summary of results from this and other works. • More efficient stripping in more massive groups/clusters (Fstrip depends on Mcl, V, T etc; Bekki et al. 2002; Bekki 2009). • Typically 70% of gas can be removed from galaxy halos (McCarthy et al. 2008). • Stripping of halo gas is quite efficient in less luminous galaxies (Vc~150 km/s) in small groups (Kawata & Mulchaey 2008).

  11. Halo vs disk gas stripping. • The required Vrel and rIGM for halo gas stripping are significantly lower than those for disk one (~ 2000 km/s and ~ 3*10-3 atoms cm-3 ;Abadi et al. 1999; Quills et al. 2000; Vollmer et al. 2006; Tonnesen & Bryan 2008). (Quills et al. 2000)

  12. Simulating galaxy evolution after halo gas stripping. • Decrease of gas infall rate disappearance of spiral arms in disk galaxies  S0 formation ? • Evolution from blue to red spirals with ``k’’-type spectra ?

  13. Simulating the post-stripping evolution. Morphological evolution of disks with slow vs rapid gas accretion from halos. Md=2*1010Msun T=0 Gyr T~ 3 Gyr Slow accretion Rapid accretion Slow accretion Rapid accretion Revisiting the Sellwood & Carlberg (1984) model by using a more realist model e.g., with NFW DM halo, exponential disk/bulge etc (Bekki 2009).

  14. Slow (dM/dt=0.7 Msun/yr) Rapid (dM/dt=7 Msun/yr)

  15. Simulating the post-stripping evolution. Bar formation in growing disks via halo gas infall. Md=5*1010Msun T~ 3 Gyr T~ 0 Gyr Without accretion With accretion Without With accretion Revisiting the Sellwood & Carlberg (1984) model by using a more realist model e.g., with NFW DM halo, exponential disk/bulge etc (Bekki 2009).

  16. Without ``gas accretion’’ With ``gas accretion’’

  17. Implications of the results. • Gradual transformation of spirals into S0s and passive spirals due to halo gas stripping in groups/clusters (e.g., Larson et al.1980; Bekki et al. 2002). • Suppression of star formation due to high Q and low gas mass fraction Strangulation (e.g., Balogh et al. 2000). • A smaller fraction of barred galaxies among S0s (fraction of bars is 46% in S0s and 70% in spirals: Laurikainen et al. 2009). • Evolution from satellite galaxies into the red sequence through SF suppression (e.g., van den Bosch et al. 2008).

  18. (II) Galaxy interaction • Two major roles: Morphological transformation (e.g., SpSB) and triggering starbursts (e.g. Noguchi 1987; Noguchi & Ishibashi 1987 and many others). Bar formation during tidal interaction (Noguchi 1987).

  19. Timescale of galaxy interaction/merging. Formula by Makino & Hut (1997) Galaxy interaction <tH Major merging of MW-type galaxy >tH For a cluster with Mcl=1014 Msun (NFW), and a MW-type galaxy

  20. Galaxy interaction in different environments. Rp • Three basic parameters: Peri-center distance (Rp), relative velocity (Vrel), and mass ratio (m2), which depend strongly on environments. • Dependence of interaction physics on the Hubble types and gas fraction. Vrel m2 Interaction strength dependent on three parameters. e.g., Vrel ~ F(Mclust) (Byrd et al. 1990; Berentzen et al. 1999 Perez et al. 2006 etc.)

  21. Formation of bars and starbursts in fast galaxy encounters with vrel=1000 km/s. Stars New stars Companion galaxy (Same Rp=35 kpc, Bulge-less spirals, MW-class disks). m2=1 m2=5 (Bekki 2009)

  22. Star formation histories during fast encounters (Vrel~ 1000 km/s). SFR MB/MB+Md=0.0 Peri-center passage  Galaxy interaction in clusters of galaxies

  23. Star formation histories during slow encounters (Vrel ~ 300 km/s). SFR m2=1.0 MB/MB+Md=0.4 Peri-center passage  Galaxy interaction in groups

  24. Implications • More dramatic changes in SF histories of low-luminosity systems in clusters (The BO effect can be for less luminous systems ?). • Early-type spirals are unlikely to show enhanced SF activities (e.g., e(c) and e(b) spectral types) irrespective of environments. • Starburst spectra only in the inner regions.

  25. (III) Cluster/group tides • Morphological transformation (e.g., S0 formation; Byrd & Valtonen 1990), triggering starbursts, and tidal truncation of gaseous halos. • Formation of dEs from galaxy harassment (i.e., combination of cluster tide and high-speed multiple galaxy interaction; Moore et al. 1996).

  26. Morphological transformation. (I) From early-type spirals to S0s (Cluster tide) (Byrd & Valtonen 1990). (II) From bulge-less, less luminous spirals to dEs. (Moore et al. 1996) (Harassment) (III) From dE,Ns to UCDs (Threshing) (Bekki et al. 2001)

  27. Tidal effects of the Fornax cluster on a nucleated dwarf with MV=-16 mag.

  28. Orbit-dependent galaxy evolution. Cluster-centric distance (kpc) Rs (NFW) Mcl=1014 Msun (NFW) SFR (Msun/yr) Starburst Time (Bekki 2009)

  29. Implications • A higher fraction of starburst galaxies in cores of clusters/groups ? • BO blue galaxies would be less luminous disks with small bulges (if cluster tide is responsible for the BO effect).

  30. (IV) Mergers in small/compact groups. • Evolution of compact groups into giant elliptical galaxies through multiple mergers (e.g., Barnes 1989). • Formation and evolution of ``fossil groups’’ (e.g., Ponman et al. 1994; Mendes de Oliveira et al. 2007). • Chance projection (Mamon 1986) and 30% of true compact groups (Brasseur et al. 2009) ? HCG90 [HST image By R. Sharples]

  31. Galaxy evolution dependent on galaxy density/kinematics and gas content. rgal Trot fg Properties of merger remnants dependent on three parameters. (2T/|W|=1 i.e., in vrial equilibrium) • Uniform or King distribution ? • Trot/T=1 or 0. • Gas mass fraction (fg)=0 or 0.5. (Bekki 2009)

  32. Multiple mergers and elliptical galaxy formation. (Bekki 2009)

  33. Multiple mergers and formation of a binary galaxy (E-E). (Bekki 2009; See also Wiren et al. 1996)

  34. Formation of a ``fossil group’’. 350 kpc 1st 2nd A factor of 10 (~2.5 mag) luminosity difference between the 1st and 2nd largest galaxies. Schechter LF function (a=-1 for 20 galaxies)

  35. Evolution of gas-rich disks in small/compact groups. Gaseous evolution Final Intra-group HI gas/rings  Giant gas disk around a spheroid (Bekki 2009)

  36. Formation of starburst and post-starburst galaxies. Post-starburst Starburst Star-forming ULIRG/QSO phase SFR (Bekki 2009) Time

  37. Implications. • Binary galaxy formation (e.g., E-E pair) from small/compact groups ? • Origin of ``E+A’’s with companions (e.g. Goto 2001; 2008): Transition phase of small/compact groups ? (A pair galaxy: Hernandez-Toledo et al. 2006) (SDSS image of E+As Yamauchi et al. 2008)

  38. (V) Galaxy evolution during environmental changes. • Observational evidences of merging clusters/groups, e.g., substructures and cold-fronts (e.g. Forman & Jones 1990 Owen et al. 2008). • The growth of groups/clusters via accretion of smaller groups in hierarchical clustering scenarios (12-30%, Li & Helmi 2008; Berrier et al. 2009). X-ray iso-intensity contour (Forman & Jones 1990)

  39. Effects of time-changing tides and IGM in merging groups/clusters. • Morphological transformation from spirals into S0s due to strong tidal fields (Bekki 1999; Gnedin 2003). • Enhancement of star formation by high IGM pressure (Evrard 1991) or suppression of SF by gas stripping (Fujita et al. 1999) ?

  40. Simulating IGM effects on galaxies: triggering starbursts ? • Time evolution of gas pressure of IGM around galaxies in merging clusters. • Mclust ~1014 Msun, Rvir ~ 1 Mpc, Vrel~ 600 km/s. Merging clusters IGM (Bekki 2009) 100 galaxy particles Pressure ?

  41. Dramatic increase of IGM pressure around galaxies during group/cluster merging. Pressure ( x 105 kB K cm-3) Internal pressure of GMCs. Ram-pressure-induced Starbursts: Bekki & Couch (2003), Kronberger etr al. (2008) Time (Gyr)

  42. Synchronized global starbursts ? Pmax,mer The mean Pmax,mer/Pmax,iso=5.9 T=2 Gyr Pmax,iso=Pmax,mer (Galaxy passage of high-pressure IGM of merging clusters) Pmax,iso

  43. Substructures of galaxies experiencing high-pressure/density IGM. Rvir Galaxy particles M2/M1=0.25 (Bekki 2009)

  44. Implications • Ahigher fraction of starburst/post-starburst galaxies in merging clusters (e.g., Miller et al. 2003; Owen et al 2005 for Abel 2255 and 2125, respectively) ? (HST image Of A2125). (0.5-2 kev Chandra image with radio sources)

  45. Implications • A clue to the origin of post-starburst galaxies in the substructure of the Coma cluster (e.g., Poggianti et al. 2004). • Stronger BO effects in clusters with substructures ?

  46. Conclusions • Efficient halo gas stripping in groups/clusters Suppression of star formation and gradual morphological transformation. • Cluster/galaxy tide Dramatic changes in star-forming regions and rapid morphological transformation. • Synchronized formation of starbursts during group/cluster merging  Differences in galaxy properties between clusters with/without substructures.

  47. Spectrophotometric evolution of disks after gas stripping. Rapid Slow No No truncation Rapid truncation Slow Spectral evolution: e(b)e(a)a+kk+a k. (Shioya et al. 2002, 2004).

  48. Spectral types dependent on galactic morphological types. Sa Sc Number • Number fraction of Sa and Sc with e(a), e(b), and e(c) is 0.1 and 0.48, respectively (Poggianti et al. 1999) Selective influence of galaxy interaction ? e(b) e(a) e(c) Late Early (Poggianti et al. 2008)

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