The Evolution of Intracluster Light

1
The Evolution of Intracluster Light

• Craig Rudick
• Department of Astronomy
• Case Western Reserve University

2
Collaborators

• Chris Mihos
• Cameron McBride (now at U. of Pittsburgh)
• Andrew Schechtman-Rook (now at U. of Wisconsin)
• All Images and Figures from Rudick, Mihos,
  Mcbride, 2006, ApJ, 648, 936

3
Outline

• What is ICL? Thanks Chris!
• Simulating ICL
• Simulated Observations

4
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
• Resimulate to z0

5
Simulated Observations

• Discrete particles are smoothed using an adaptive
  Gaussian smoothing kernel
• Apply a global mass-to-light ratio
• M/L 5 (solar units) in V
• 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
• Taken from same cosmology

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Defining ICL

• Previously used definitions
• Theory unbound particles (stars)
• Unobservable in broadband imaging
• Observation excess over galactic profiles
• 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
• Holmberg Radius

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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 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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ICL Kinematics
Velocity Dispersion
Mean Velocity

• ICL kinematics can be traced using PNe velocities
• Work in progress!

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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