The Evolution of Intracluster Light Craig Rudick Department of Astronomy Case Western Reserve University

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

Outline What is ICL? – Thanks Chris! What is ICL? – Thanks Chris! Simulating ICL Simulating ICL Simulated Observations Simulated Observations

Simulating Clusters Start with a  CDM, dark matter only cosmological N-body simulation Start with a  CDM, dark matter only cosmological N-body simulation At z=0 identify massive clusters At z=0 identify massive clusters Trace cluster particles back to z=2 Trace cluster particles back to z=2 Populate DM halos with hi-res luminous galaxies models Populate DM halos with hi-res luminous galaxies models Resimulate to z=0 Resimulate to z=0

Simulated Observations Discrete particles are smoothed using an adaptive Gaussian smoothing kernel Discrete particles are smoothed using an adaptive Gaussian smoothing kernel Apply a global mass-to-light ratio 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 z=0 –All evolution is due to gravitational dynamics!

Presented in Technicolor 3 clusters 3 clusters –~10 14 solar masses –From z=2 to z=0 –Taken from same cosmology

Defining ICL Previously used definitions: Previously used definitions: –Theory: unbound particles (stars) Unobservable in broadband imaging Unobservable in broadband imaging –Observation: excess over galactic profiles Model dependent, not universally applicable Model dependent, not universally applicable We define ICL as luminosity fainter than  V of 26.5 mag/sq. arcsec We define ICL as luminosity fainter than  V of 26.5 mag/sq. arcsec –Well-defined observable –Radius at which ICL has unique morphology –Holmberg Radius

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

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

Cluster 2 Small group crashes through large central group from bottom left to top right Small group crashes through large central group from bottom left to top right –ICL increase coincides with galaxy exiting center

ICL Kinematics ICL kinematics can be traced using PNe velocities ICL kinematics can be traced using PNe velocities Work in progress! Work in progress! Mean Velocity Velocity Dispersion

Conclusions ICL luminosity tends to increase with dynamical time ICL luminosity tends to increase with dynamical time ICL luminosity increases are strongly correlated with group accretion events ICL luminosity increases are strongly correlated with group accretion events ICL features are tracers of cluster’s evolutionary history ICL features are tracers of cluster’s evolutionary history