The origin and properties of intracluster stars in a rich cluster
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abstract
We use a multi million particle N-body + SPH simulation to follow the
formation of a rich galaxy cluster in a Lambda+CDM cosmology, with the goal of
understanding the origin and properties of intracluster stars. The simulation
includes gas cooling, star formation, the effects of a uniform UVB and feedback
from supernovae. Halos that host galaxies as faint as M_R = -19.0 are resolved
by this simulation, which includes 85% of the total galaxy luminosity in a rich
cluster. We find that the accumulation of intracluster light (ICL) is an
ongoing process, linked to infall and stripping events. The unbound star
fraction increases with time and is 20% at z = 0, consistent with observations
of galaxy clusters. The surface brightness profile of the cD shows an excess
compared to a de Vaucouleur profile near 200 kpc, which is also consistent with
observations. Both massive and small galaxies contribute substantially to the
formation of the ICL, with stars stripped preferentially from the outer parts
of their stellar distributions. Simulated observations of planetary nebulae
(PNe) show significant substructure in velocity space. Despite this, individual
intracluster PNe might be useful mass tracers if more than 5 fields at a range
of radii have measured line-of-sight velocities, where an accurate mass
calculation depends more on the number of fields than the number of PNe
measured per field. However, the orbits of IC stars are more anisotropic than
those of galaxies or dark matter, which leads to a systematic underestimate of
cluster mass relative to that calculated with galaxies, if not accounted for in
dynamical models. Overall, the properties of ICL formed in a hierarchical
scenario are in good agreement with current observations. (Abridged)
