Simulating the Production of Intra-Cluster Light

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Simulating the Production of Intra-Cluster Light

• Craig Rudick
• Department of Astronomy
• CERCA - 02/17/05

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Collaborators

• Chris Mihos
• Cameron McBride (now at U. of Pittsburgh)

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Outline

• What is ICL?
• How do we simulate it?
• What can we learn from it?

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Excess Cluster Luminosity

• Intra-Cluster Light is stellar luminosity in
  clusters originating outside the cluster
  galaxies
• All stars are formed in galaxies how do they
  get out?

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Tidal Stripping

• Clusters are massive potential wells
• Cluster galaxies experience large tidal fields
• Stars are ripped right out of the galactic
  potentials

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Really Freaking Faint

• ICL features are typically lt1 of sky brightness.

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Simulating Clusters

• Start with a LCDM, dark matter only cosmological
  N-body simulation
• At z0 identify massive clusters
• Trace cluster particles back to z2
• Populate DM halos with hi-res luminous galaxies
  models using HOD
• Resimulate to z0

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Simulations (cont.)

• Maintains large scale mass structure
• Allows realistic modeling of initial mass
  distribution and accretion
• Cosmic variance of cluster properties
• N-body only no hydro

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Simulated Observations

• Discrete particles are smoothed using an adaptive
  Gaussian smoothing kernel
• Smoothing length proportional to local density
• Apply a global mass-to-light ratio
• No star formation, stellar evolution, surface
  brightness dimming, etc.
• Observing dynamical state of clusters as they
  would appear at z0
• All evolution is due to gravitational dynamics!

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Presented in Technicolor

• 3 clusters
• 1014 solar masses
• From z2 to z0

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Defining ICL

• Previously used definitions
• Theory unbound particles (stars)
• Unobservable in broadband imaging
• Observation excess over r1/4
• Model dependent, not universally applicable
• We define ICL as luminosity fainter than mV of
  26.5 mag/sq. arcsec
• Well-defined observable
• Radius at which ICL has unique morphology

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ICL Luminosity with Time

• The fraction of luminosity at ICL surface
  brightness tends to increases with time
• Increases are very stochastic and non-uniform
• Each cluster has a unique ICL history

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Changes in ICL Luminosity

• Fractional change in luminosity per unit time
• ICL luminosity increases tend to come in short,
  discrete events
• Increases in ICL luminosity are highly correlated
  with group accretion events

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Cluster 1

• Three large galaxy complexes
• The three groups do not merge
• Very little production of ICL

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Cluster 2

• Small group crashes through large central group
  from bottom left to top right
• ICL increase coincides with galaxy exiting center

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Cluster 3

• Massive collapse of groups
• Luminosity shifts to higher surface brightness as
  groups infall
• Huge ICL production after event

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Conclusions

• ICL luminosity tends to increase with dynamical
  time
• ICL luminosity increases are strongly correlated
  with group accretion events
• ICL features are tracers of clusters
  evolutionary history

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You ask, Im a cosmologist why do I care?

• Clusters are extremely important tools in
  observational cosmology
• S-Z effect
• Gravitational lensing
• Large-scale structure and matter density
• FP , T-F, SBF calibrated using cluster galaxies
• Bulk motion cosmic homgeneity