Studying the faint features of galaxy clusters, such as low surface brightness tidal streams surrounding galaxies and the distribution of diuse light inside clusters, will provide a deeper understanding of the evolutionary history of galaxies and clusters. We are particularly interested in studying the spatial correlation between the distributions of intracluster light (ICL) and the cluster substructures, obtained via weak gravitational lensing mass reconstruction and/or galaxy number density. These correlations can shed light on the origin of the ICL and its connection to the evolutionary history of the clusters.
ICL is the light from stars that are bound to the cluster but not to the individual cluster
galaxies. As shown in galaxy cluster simulation studies (Rudick et al. 2006, 2011), the ICL
abundance increases during various dynamical exchanges of galaxies. Thus, the ICL is an effective tool to measure the evolutionary stage of galaxy clusters. And the investigation of the ICL evolution mechanism will allow us understand the galaxy evolution process therein.
Correlating the ICL with weak lensing mass maps will also allows us to probe the relative
distribution of dark and baryonic matter. We expect that the ICL may be an effective tracer
of dark matter, since its dispersion is smoother than galaxy stars. Furthermore, the ICL traces directly the baryonic substructure evolution which could ll the gap in our understanding of cosmological simulations and observations, by constraining the most uncertain parts such as the star formation model and the distribution of the baryonic matter in galaxy clusters. (Arnaboldi & Gerhard 2010). In the context of measuring cluster baryon fraction, the ICL could be linked back to the early universe cosmology.
However, observing the ICL possess a signicant observational challenge due to its faint
nature, with typical brightnesses 100 times dimmer than the sky background. With the deep LSST images, we will be able to measure the ICL with a large, uniform sample of nearby clusters (including groups), and to probe the fraction of the ICL ranging from a few to a half percent of the total cluster/group light. These observational results will provide strong constraints on the current numerical simulations, particularly with respect to hierarchical merging process.
We are currently studying the ICL in clusters both at low redshift (Coma cluster; ) and at
high (z 1:3) using deep optical images from the 8.2m Subaru Telescope (Yoo et al. 2017,
in preparation) and HST telescope (Ko et al. 2017, in preparation), respectively.
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Galaxy Cluster as link between astrophysics and cosmology
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What ICL tells us about galaxy cluster
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