Simulating environmental effects: Stripping, interaction,

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Simulating environmental effects Stripping,
interaction, feedback.

• Kenji Bekki (University of New South Wales,
  Australia).

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Todays 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.

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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
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(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
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Ram pressure (Pram) vs restoring force of halo
and disk gas (Fhalo and Fdisk)
Cluster-centric distance (kpc)
200kpc
Mcl1014Msunrs260kpc (NFW), Fb0.14.
50kpc
PramrIGMv2 (sim. units)
Fdisk
Fhalo
For MW-type disk galaxy
Time
(Bekki 2009)
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Simulating halo gas stripping.
(DM halo bulge disk stars/gas halo gasSF)
Animation
Halo gas
Disk gas
Hot gas
V500 km/s T107 K (Mcl1014 Msun) Md61010Msun,v
c220 km/s,B/D0.2
(Bekki 2009)
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GRAPE7-SPH simulation Halo gas stripping (Bekki
et al 2002 2009).
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Efficiency of gas stripping in different
environments.
Mg
Time
Fstrip0.65 (Halo)

• (V500 km/s, rIGM410-3 atoms/cm3,
• T107 K Mcl1014 Msun ,
• R200kpc)

(Bekki 2009)
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Cluster Fstrip0.65 (Halo)
(V500 km/s, T107 K Mcl1014 Msun )
Group Fstrip0.38 (Halo)
(V200 km/s, T3106 K Mcl1013 Msun )
(Bekki 2009)
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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 (Vc150 km/s) in small groups
  (Kawata Mulchaey 2008).

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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 310-3 atoms cm-3
  Abadi et al. 1999 Quills et al. 2000 Vollmer
  et al. 2006 Tonnesen Bryan 2008).

(Quills et al. 2000)
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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 ?

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Simulating the post-stripping evolution.
Morphological evolution of disks with slow vs
rapid gas accretion from halos.
Md21010Msun
T0 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).
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Slow (dM/dt0.7 Msun/yr)
Rapid (dM/dt7 Msun/yr)
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Simulating the post-stripping evolution.
Bar formation in growing disks via halo gas
infall.
Md51010Msun
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).
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Without gas accretion
With gas accretion
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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).

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(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).
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Timescale of galaxy interaction/merging.
Formula by Makino Hut (1997)
Galaxy interaction
lttH
Major merging of MW-type galaxy
gttH
For a cluster with Mcl1014 Msun (NFW), and a
MW-type galaxy
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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.)
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Formation of bars and starbursts in fast galaxy
encounters with vrel1000 km/s.
Stars
New stars
Companion galaxy
(Same Rp35 kpc, Bulge-less spirals, MW-class
disks).
m21
m25
(Bekki 2009)
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Star formation histories during fast encounters
(Vrel 1000 km/s).
SFR
MB/MBMd0.0
Peri-center passage
? Galaxy interaction in clusters of galaxies
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Star formation histories during slow encounters
(Vrel 300 km/s).
SFR
m21.0
MB/MBMd0.4
Peri-center passage
? Galaxy interaction in groups
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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.

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(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).

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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)
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Tidal effects of the Fornax cluster on a
nucleated dwarf with MV-16 mag.
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Orbit-dependent galaxy evolution.
Cluster-centric distance (kpc)
Rs (NFW)
Mcl1014 Msun (NFW)
SFR (Msun/yr)
Starburst
Time
(Bekki 2009)
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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).

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(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
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Galaxy evolution dependent on galaxy
density/kinematics and gas content.
rgal
Trot
fg
Properties of merger remnants dependent on three
parameters.
(2T/W1 i.e., in vrial equilibrium)

• Uniform or King distribution ?
• Trot/T1 or 0.
• Gas mass fraction (fg)0 or 0.5.

(Bekki 2009)
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Multiple mergers and elliptical galaxy formation.
(Bekki 2009)
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Multiple mergers and formation of a binary galaxy
(E-E).
(Bekki 2009 See also Wiren et al. 1996)
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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)
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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)
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Formation of starburst and post-starburst
galaxies.
Post-starburst
Starburst
Star-forming
ULIRG/QSO phase
SFR
(Bekki 2009)
Time
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Implications.

• Binary galaxy formation (e.g., E-E pair) from
  small/compact groups ?
• Origin of EAs with companions (e.g. Goto
  2001 2008) Transition phase of small/compact
  groups ?

(A pair galaxy Hernandez-Toledo et al. 2006)
(SDSS image of EAs Yamauchi et al. 2008)
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(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)
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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) ?

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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 ?
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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)
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Synchronized global starbursts ?
Pmax,mer
The mean Pmax,mer/Pmax,iso5.9
T2 Gyr
Pmax,isoPmax,mer
(Galaxy passage of high-pressure IGM of merging
clusters)
Pmax,iso
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Substructures of galaxies experiencing
high-pressure/density IGM.
Rvir
Galaxy particles
M2/M10.25
(Bekki 2009)
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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 image Of A2125).
(0.5-2 kev Chandra image with radio sources)
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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 ?

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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.

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Spectrophotometric evolution of disks after gas
stripping.
Rapid
Slow
No
No truncation
Rapid truncation
Slow
Spectral evolution e(b)?e(a)?ak?ka? k.
(Shioya et al. 2002, 2004).
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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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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.

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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 ? EAs ? red sequence.

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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 ? EAs ? red sequence.

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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 EAs with
  companions during group evolution.

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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.

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Effects of halo gas stripping on recycling
processes in galaxies.
Animation
Halo gas
Interaction between halo and ejecta
Gas ejection
Disk
Bulge
(rg10-5 cm-3, Mejecta108 Msun, Vejecta1000
km/s)
(Bekki 2009)
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Trapping of starburst ejecta due to halo-ejecta
hydrodynamical interaction (Bekki et al. 2009).
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(III) Cluster/group tides
A less luminous disk in a cluster with
Mcl1014Msun (Bekki 2009)