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)