Simulating the Production of Intra-Cluster Light

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

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

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

“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?

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

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

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

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

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 z=0 • All evolution is due to gravitational dynamics!

Presented in Technicolor • 3 clusters • ~1014 solar masses • From z=2 to z=0

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

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

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

Cluster 1 • 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 • ICL increase coincides with galaxy exiting center

Cluster 3 • 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 increases are strongly correlated with group accretion events • 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 • S-Z effect • Gravitational lensing • Large-scale structure and matter density • FP , T-F, SBF calibrated using cluster galaxies • Bulk motion – cosmic homgeneity

Simulating the Production of Intra-Cluster Light