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.• Time-changing cluster tidal fields and IGM
during the growth of groups/clusters via hierarchical merging.
Structure of the talk
• Simulations of environmental effects (with animations).
• Implication of the results (which would help observers to interpret their results).
Simulations
ObservationsComparison
(Hickson compact group 40)[Subaru image]
(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).
Halo gas
Gas disk
A cluster of galaxies IGM
Ram pressure (Pram) vs restoring force of halo and disk gas (Fhalo and Fdisk)
(Bekki 2009)
Mcl=1014Msunr
s=260kpc (NFW),Fb=0.14.
Cluster-centric distance (kpc)
Pram=IGM*v2
(sim. units)
Time
Fdisk
FhaloFor MW-type disk galaxy
200kpc
50kpc
Simulating halo gas stripping.
Hot gasDisk gas
Halo gas
V=500 km/s T=107 K (Mcl=1014 Msun)Md=6*1010Msun,vc=220 km/s,B/D=0.2
(DM halo + bulge + disk stars/gas + halo gas+SF)
(Bekki 2009)
Animation
GRAPE7-SPH simulation: Halo gas stripping (Bekki et al 2002; 2009).
Efficiency of gas stripping in different environments.
(V=500 km/s, IGM=4*10-3 atoms/cm3,T=107 K [Mcl=1014 Msun ],R~200kpc)
(Bekki 2009)
Fstrip=0.65 (Halo)
Mg
Time
(V=500 km/s, T=107 K [Mcl=1014 Msun ])
(Bekki 2009)
Cluster: Fstrip=0.65 (Halo)
Group: Fstrip=0.38 (Halo) (V=200 km/s, T=3*106 K [Mcl=1013 Msun ])
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).
Halo vs disk gas stripping.
• The required Vrel and IGM 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)
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 ?
Simulating the post-stripping evolution.
Revisiting the Sellwood & Carlberg (1984) model by using a more realist modele.g., with NFW DM halo, exponential disk/bulge etc (Bekki 2009).
T=0 Gyr T~ 3 Gyr
Slow accretion
Morphological evolution of disks with slow vs rapid gas accretion from halos.
Rapid accretion Slow accretion Rapid accretion
Md=2*1010Msun
Slow (dM/dt=0.7 Msun/yr) Rapid (dM/dt=7 Msun/yr)
Simulating the post-stripping evolution.
Revisiting the Sellwood & Carlberg (1984) model by using a more realist modele.g., with NFW DM halo, exponential disk/bulge etc (Bekki 2009).
Without accretion
Bar formation in growing disks via halo gas infall.
With accretion Without With accretion
T~ 3 GyrT~ 0 Gyr
Md=5*1010Msun
Without ``gas accretion’’ With ``gas accretion’’
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).
(II) Galaxy interaction• Two major roles: Morphological
transformation (e.g., SpSB) and triggering starbursts (e.g. Noguchi 1987; Noguchi & Ishibashi 1987 and many others).
Bar formation during tidal interaction(Noguchi 1987).
Timescale of galaxy interaction/merging.
For a cluster with Mcl=1014 Msun (NFW), and a MW-type galaxy
Galaxy interaction
Major merging of MW-type galaxy
Formula by Makino & Hut (1997)
<tH
>tH
Galaxy interaction in different environments.
• 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.
m2
Vrel
Rp
e.g., Vrel ~ F(Mclust)
Interaction strength dependent on three parameters.
(Byrd et al. 1990; Berentzen et al. 1999 Perez et al. 2006 etc.)
Formation of bars and starbursts in fast galaxy encounters with vrel=1000 km/s.
m2=1 m2=5 (Bekki 2009)
(Same Rp=35 kpc,Bulge-less spirals,MW-class disks).
Stars
New stars
Companiongalaxy
Star formation histories during fast encounters (Vrel~ 1000 km/s).
SFR
Galaxy interaction in clusters of galaxies
Peri-center passageMB/MB+Md=0.0
Star formation histories during slow encounters (Vrel ~ 300 km/s).
SFR
Galaxy interaction in groupsPeri-center passage
MB/MB+Md=0.4
m2=1.0
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.
(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).
Morphological transformation.(I) From early-type spirals to S0s
(III) From dE,Ns to UCDs
(II) From bulge-less, less luminous spirals to dEs.
(Cluster tide)
(Harassment)
(Threshing)
(Byrd & Valtonen1990).
(Moore et al. 1996)
(Bekki et al. 2001)
Tidal effects of the Fornax cluster on a nucleated dwarf with MV=-16 mag.
Orbit-dependent galaxy evolution.Cluster-centric distance (kpc)
SFR (Msun/yr)
Time
Starburst
(Bekki 2009)
Rs (NFW)
Mcl=1014 Msun (NFW)
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).
(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 imageBy R. Sharples]
Galaxy evolution dependent on galaxy density/kinematics and gas content.
fg
Trot
gal
Properties of merger remnants dependent on three parameters.
(A)Uniform or King distribution ?(B)Trot/T=1 or 0.(C)Gas mass fraction (fg)=0 or 0.5.
(2T/|W|=1 i.e., in vrial equilibrium)
(Bekki 2009)
Multiple mergers and elliptical galaxy formation.
(Bekki 2009)
Multiple mergers and formation of a binary galaxy (E-E).
(Bekki 2009; See also Wiren et al. 1996)
Formation of a ``fossil group’’.350 kpc
A factor of 10 (~2.5 mag)luminosity differencebetween the 1st and 2nd largest galaxies.
Schechter LF function(=-1 for 20 galaxies)
1st
2nd
Evolution of gas-rich disks in small/compact groups.
Gaseous evolution
Intra-group HI gas/rings Giant gas disk around a spheroid(Bekki 2009)
Final
Formation of starburst and post-starburst galaxies.
(Bekki 2009)
Post-starburst
Starburst
Star-forming
SFR
Time
ULIRG/QSO phase
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 ?
(SDSS image of E+As Yamauchi et al. 2008)
(A pair galaxy: Hernandez-Toledo et al. 2006)
(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)
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) ?
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. 100 galaxy particles
IGMMerging clusters
(Bekki 2009)
Pressure ?
Dramatic increase of IGM pressure around galaxies during group/cluster merging.
Pressure ( x 105 kB K cm-3)
Time (Gyr)
Internal pressure of GMCs.
Ram-pressure-induced Starbursts: Bekki & Couch (2003),Kronberger etr al. (2008)
Synchronized global starbursts ?
Pmax,mer
Pmax,iso
The mean Pmax,mer/Pmax,iso=5.9
T=2 Gyr
(Galaxy passage of high-pressureIGM of merging clusters)
Pmax,iso=Pmax,mer
Substructures of galaxies experiencing high-pressure/density IGM.
(Bekki 2009)
Rvir
Galaxy particles
M2/M1=0.25
Implications
• A higher 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 imageOf A2125).
(0.5-2 kev Chandra image with radio sources)
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 ?
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.
Spectrophotometric evolution of disks after gas stripping.
Rapid truncation
Slow
No truncation
Rapid Slow
No
(Shioya et al. 2002, 2004).
Spectral evolution: e(b)e(a)a+kk+a k.
Spectral types dependent on galactic morphological types.
• 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 ?
(Poggianti et al. 2008)
Early Late
e(a)
e(b)
e(c)
Sa ScNumber
Conclusion (I) Effects of halo/disk gas stripping on galaxy evoluion in groups/clusters
• Morphological: Gradual disappearance of spiral arms, non-development of strong bars, and disk heating S0 formation.
• Star formation: Severe suppression of SF due to low gas fraction and high Q.
• Photometric: Red passive spiral formation.
Conclusion (II) Effects of tidal interaction on galaxy
evolution in groups/clusters
• Morphological: Transformation into S0, dE, SBa/b, cE, UCD etc depending on progenitor masses, Hubble-types, and interaction strength.
• Star formation: Strong starbursts and subsequent truncation.
• Photometric: Blue E+As red sequence.
Conclusion (III) Effects of group/cluster tide on galaxy
evolution
• Morphological: Transformation into S0, dE, SBa/b, cE, UCD etc depending on progenitor masses, Hubble-types, and interaction strength.
• Star formation: Strong starbursts and subsequent truncation.
• Photometric: Blue E+As red sequence.
Conclusion (IV) Effects of merging on galaxy evolution in
compact groups
• Morphological: Transformation into giant Es, early-type spirals with extended halo/HI disks, binary galaxies depending on progenitor types and galaxy number densities.
• Star formation: Multiple starbursts and subsequent truncation.
• Photometric: Formation of E+As with companions during group evolution.
Conclusion (V) Effects of changing environments
(merging clusters) on galaxy evolution.
• Morphological: S0 formation from time-changing tidal fields and from gas stripping by IGM.
• Star formation: Synchronized starbursts and subsequent rapid truncation.
• Photometric: Substructures of post-starburst galaxies.
Effects of halo gas stripping on recycling processes in galaxies.
Animation
(Bekki 2009)
Disk
Halo gas
Bulge
Gas ejection
Interaction between halo and ejecta
(g=10-5 cm-3, Mejecta=108 Msun,Vejecta=1000 km/s)
Trapping of starburst ejecta due to halo-ejecta hydrodynamical interaction (Bekki et al. 2009).
(III) Cluster/group tides
A less luminous disk in a cluster with Mcl=1014Msun (Bekki 2009)
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