Simulating the Simulating the Production of Intra-Production of Intra-Cluster LightCluster Light

Craig RudickCraig RudickDepartment of AstronomyDepartment of AstronomyCERCA - 02/17/05CERCA - 02/17/05

CollaboratorsCollaborators

Chris MihosChris Mihos Cameron McBride (now at U. of Cameron McBride (now at U. of

Pittsburgh)Pittsburgh)

OutlineOutline

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 Excess” Cluster LuminosityLuminosity Intra-Cluster Light is stellar Intra-Cluster Light is stellar

luminosity in clusters originating luminosity in clusters originating “outside” the cluster galaxies“outside” the cluster galaxies

All stars are formed in galaxies – All stars are formed in galaxies – how do they get out?how do they get out?

Tidal StrippingTidal Stripping

Clusters are massive potential Clusters are massive potential wellswells

Cluster galaxies experience large Cluster galaxies experience large tidal fields tidal fields

Stars are ripped right out of the Stars are ripped right out of the galactic potentialsgalactic potentials

Really Freaking FaintReally Freaking Faint

ICL features are typically <1% of sky ICL features are typically <1% of sky brightness.brightness.

Simulating ClustersSimulating Clusters

Start with a Start with a CDM, dark matter only CDM, dark matter only cosmological N-body simulationcosmological N-body simulation

At z=0 identify massive clustersAt z=0 identify massive clusters Trace cluster particles back to z=2Trace cluster particles back to z=2 Populate DM halos with hi-res Populate DM halos with hi-res

luminous galaxies models using HODluminous galaxies models using HOD Resimulate to z=0Resimulate to z=0

Simulations (cont.)Simulations (cont.)

Maintains large scale mass Maintains large scale mass structurestructure

Allows realistic modeling of initial Allows realistic modeling of initial mass distribution and accretionmass distribution and accretion

Cosmic variance of cluster Cosmic variance of cluster propertiesproperties

N-body only – no hydroN-body only – no hydro

Simulated Simulated ObservationsObservations Discrete particles are smoothed using an Discrete particles are smoothed using an

adaptive Gaussian smoothing kerneladaptive Gaussian smoothing kernel– Smoothing length proportional to local densitySmoothing length proportional to local density

Apply a global mass-to-light ratioApply a global mass-to-light ratio– No star formation, stellar evolution, surface No star formation, stellar evolution, surface

brightness dimming, etc.brightness dimming, etc.– Observing dynamical state of clusters as they Observing dynamical state of clusters as they

would appear at z=0would appear at z=0– All evolution is due to gravitational dynamics!All evolution is due to gravitational dynamics!

Presented in Presented in TechnicolorTechnicolor 3 clusters3 clusters

– ~10~101414 solar solar massesmasses

– From z=2 to From z=2 to z=0z=0

Defining ICLDefining ICL

Previously used definitions:Previously used definitions:– Theory: unbound particles (stars)Theory: unbound particles (stars)

Unobservable in broadband imagingUnobservable in broadband imaging

– Observation: excess over rObservation: excess over r1/41/4 Model dependent, not universally applicableModel dependent, not universally applicable

We define ICL as luminosity fainter than We define ICL as luminosity fainter than VV of 26.5 mag/sq. arcsec of 26.5 mag/sq. arcsec– Well-defined observableWell-defined observable– Radius at which ICL has unique morphologyRadius at which ICL has unique morphology

ICL Luminosity with ICL Luminosity with TimeTime The fraction of The fraction of

luminosity at ICL luminosity at ICL surface surface brightness tends brightness tends to increases with to increases with timetime

Increases are Increases are very stochastic very stochastic and non-uniformand non-uniform

Each cluster has a Each cluster has a unique ICL historyunique ICL history

Changes in ICL Changes in ICL LuminosityLuminosity Fractional change in Fractional change in

luminosity per unit luminosity per unit timetime

ICL luminosity ICL luminosity increases tend to increases tend to come in short, come in short, discrete eventsdiscrete events

Increases in ICL Increases in ICL luminosity are highly luminosity are highly correlated with correlated with group accretion group accretion eventsevents

Cluster 1Cluster 1 Three large galaxy complexesThree large galaxy complexes

– The three groups do not mergeThe three groups do not merge– Very little production of ICLVery little production of ICL

Cluster 2Cluster 2 Small group crashes through Small group crashes through

large central group from large central group from bottom left to top rightbottom left to top right– ICL increase coincides with ICL increase coincides with

galaxy exiting centergalaxy exiting center

Cluster 3Cluster 3

Massive collapse of groupsMassive collapse of groups– Luminosity shifts to higher surface Luminosity shifts to higher surface

brightness as groups infallbrightness as groups infall– Huge ICL production after eventHuge ICL production after event

ConclusionsConclusions

ICL luminosity tends to increase ICL luminosity tends to increase with dynamical timewith dynamical time

ICL luminosity increases are ICL luminosity increases are strongly correlated with group strongly correlated with group accretion eventsaccretion events

ICL features are tracers of ICL features are tracers of cluster’s evolutionary historycluster’s evolutionary history

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

tools in observational cosmologytools in observational cosmology– S-Z effectS-Z effect– Gravitational lensingGravitational lensing– Large-scale structure and matter Large-scale structure and matter

densitydensity– FP , T-F, SBF calibrated using cluster FP , T-F, SBF calibrated using cluster

galaxiesgalaxies– Bulk motion – cosmic homgeneityBulk motion – cosmic homgeneity