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Register a new userThe Formation and Evolution of Intracluster Light
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Using N-body simulations, we have modeled the production and evolution of diffuse, low surface brightness intracluster light (ICL) in three simulated galaxy clusters. Using an observational definition of ICL to be luminosity at a surface brightness mu_V>26.5 mag/sq.arcsec, we have found that the fraction of cluster luminosity contained in ICL generally increases as clusters evolve, although there are large deviations from this trend over short timescales, including sustained periods of decreasing ICL luminosity. Most ICL luminosity increases come in short, discrete events which are highly correlated with group accretion events within the cluster. In evolved clusters we find that ~10-15% of the clusters luminosity is at ICL surface brightness. The morphological structure of the ICL changes with time, evolving from a complex of filaments and small-scale, relatively high surface brightness features early in a clusters history, to a more diffuse and amorphous cluster-scale ICL envelope at later times. Finally, we also see a correlation between the evolution of ICL at different surface brightnesses, including a time delay between the evolution of faint and extremely faint surface brightness features which is traced to the differing dynamical timescales in the group and cluster environment.
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We present some early results from our deep imaging survey of galaxy clusters intended to detect and study intracluster light (ICL). From our observations to date, we find that ICL is common in galaxy clusters, and that substructure in the ICL also appears to be common as well. We also discuss some initial comparisons of our imaging results to high-resolution numerical simulations of galaxy clusters, and give avenues for future research.
The largest stellar halos in the universe are found in massive galaxy clusters, where interactions and mergers of galaxies, along with the cluster tidal field, all act to strip stars from their host galaxies and feed the diffuse intracluster light (ICL) and extended halos of brightest cluster galaxies (BCGs). Studies of the nearby Virgo Cluster reveal a variety of accretion signatures imprinted in the morphology and stellar populations of its ICL. While simulations suggest the ICL should grow with time, attempts to track this evolution across clusters spanning a range of mass and redshift have proved difficult due to a variety of observational and definitional issues. Meanwhile, studies of nearby galaxy groups reveal the earliest stages of ICL formation: the extremely diffuse tidal streams formed during interactions in the group environment.
We first present the results of numerical simulations on formation processes and physical properties of old globular clusters (GCs) located within clusters of galaxies (``intracluster GCs) and in between clusters of galaxies (``intercluster GCs). Our high-resolution cosmological simulations with models of GC formation at high redshifts ($z>6$) show that about 30 % of all GCs in a rich cluster can be ragarded as intracluster GCs that can freely drift being trapped by gravitational potential of the cluster rather than by the cluster member galaxies. The radial surface density profiles of the simulated intracluster GCs are highly likely to be flatter than those of GCs within cluster member galaxies. We also find that about 1% of all GCs formed before $z>6$ are not located within any virialized halos and can be regarded as ``intercluster (or ``intergalactic) GCs. We discuss the dependences of physical properties of intracluster and intercluster GCs on the initial density profiles of GCs within low-mass dark matter halos at high redshifts ($z>6$).
We examine the outskirts of galaxy clusters in the C-EAGLE simulations to quantify the `edges of the stellar and dark matter distribution. The radius of the steepest slope in the dark matter, commonly used as a proxy for the splashback radius, is located at ~r_200m; the strength and location of this feature depends on the recent mass accretion rate, in good agreement with previous work. Interestingly, the stellar distribution (or intracluster light, ICL) also has a well-defined edge, which is directly related to the splashback radius of the halo. Thus, detecting the edge of the ICL can provide an independent measure of the physical boundary of the halo, and the recent mass accretion rate. We show that these caustics can also be seen in the projected density profiles, but care must be taken to account for the influence of substructures and other non-diffuse material, which can bias and/or weaken the signal of the steepest slope. This is particularly important for the stellar material, which has a higher fraction bound in subhaloes than the dark matter. Finally, we show that the `stellar splashback feature is located beyond current observational constraints on the ICL, but these large projected distances (>> 1 Mpc) and low surface brightnesses (mu >> 32 mag/arcsec^2) can be reached with upcoming observational facilities such as the Vera C. Rubin Observatory, the Nancy Grace Roman Space Telescope, and Euclid.
Observations of 170 local ($zlesssim0.08$) galaxy clusters in the northern hemisphere have been obtained with the Wendelstein Telescope Wide Field Imager (WWFI). We correct for systematic effects such as point-spread function broadening, foreground star contamination, relative bias offsets, and charge persistence. Background inhomogeneities induced by scattered light are reduced down to $Delta {rm SB} > 31~g$ mag arcsec$^{-2}$ by large dithering and subtraction of night-sky flats. Residual background inhomogeneities brighter than ${rm SB}_{sigma}< 27.6~g$ mag arcsec$^{-2}$ caused by galactic cirrus are detected in front of 23% of the clusters. However, the large field of view allows discrimination between accretion signatures and galactic cirrus. We detect accretion signatures in the form of tidal streams in 22%, shells in 9.4%, and multiple nuclei in 47% of the Brightest Cluster Galaxies (BCGs) and find two BCGs in 7% of the clusters. We measure semimajor-axis surface brightness profiles of the BCGs and their surrounding Intracluster Light (ICL) down to a limiting surface brightness of ${rm SB} = 30~g$ mag arcsec$^{-2}$. The spatial resolution in the inner regions is increased by combining the WWFI light profiles with those that we measured from archival textit{Hubble Space Telescope} images or deconvolved WWFI images. We find that 71% of the BCG+ICL systems have surface brightness (SB) profiles that are well described by a single Sersic (SS) function, whereas 29% require a double Sersic (DS) function to obtain a good fit. We find that BCGs have scaling relations that differ markedly from those of normal ellipticals, likely due to their indistinguishable embedding in the ICL.
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