Simulating the Production of Intra-Cluster Light Craig Rudick Department of Astronomy CERCA - 02/17/05

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

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

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

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

Really Freaking Faint ICL features are typically <1% of sky brightness. ICL features are typically <1% of sky brightness.

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 using HOD Populate DM halos with hi-res luminous galaxies models using HOD Resimulate to z=0 Resimulate to z=0

Simulations (cont.) Maintains large scale mass structure Maintains large scale mass structure Allows realistic modeling of initial mass distribution and accretion Allows realistic modeling of initial mass distribution and accretion Cosmic variance of cluster properties Cosmic variance of cluster properties N-body only – no hydro N-body only – no hydro

Simulated Observations Discrete particles are smoothed using an adaptive Gaussian smoothing kernel Discrete particles are smoothed using an adaptive Gaussian smoothing kernel –Smoothing length proportional to local density Apply a global mass-to-light ratio 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 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

Defining ICL Previously used definitions: Previously used definitions: –Theory: unbound particles (stars) Unobservable in broadband imaging Unobservable in broadband imaging –Observation: excess over r 1/4 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

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

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

Cluster 3 Massive collapse of groups Massive collapse of groups –Luminosity shifts to higher surface brightness as groups infall –Huge ICL production after event

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

You ask, “I’m a cosmologist – why do I care?” Clusters are extremely important tools in observational cosmology 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