we developed an alternative simulation technique referred to as the “Galaxy Replacement Technique” (GRT). The GRT focuses on following the buildup of a cluster with a multiresolution cosmological N-body resimulation, derived from the full merger tree of a low-resolution DM-only cosmological simulation of a cluster. As this technique utilizes a resimulation approach, we can choose and control the properties and time evolution of the cluster while still fully considering their cosmological context. This means that we can target various clusters with, for example, particular merger histories or environments, depending on the focus of our study. Moreover, the GRT traces the spatial distribution and evolution of the cluster and its substructures without the inclusion of computationally expensive baryonic physics. This inexpensive calculation enables us to study large statistical samples of clusters with both high mass and high spatial resolution, which is critical for providing predictions on very low surface brightness features. The high spatial resolution allows us to resolve the tidal stripping process accurately, and the high mass resolution allows us to model diffuse features with sufficient star particles. Thus, the GRT is ideal for a statistical study of ICL formation in a cosmological context. More details can be found in Chun et al. 2022.
[Cartoon schematic of the time evolution of a halo that reaches Mpeak at treplace. (a) The halo is composed of the low-resolution DM particles (black filled circles) until treplace. (b) The particles in the virial radius of the halo (green dashed circle) are replaced by a high-resolution DM (gray scale) and stellar disk (blue scale) and then (c) fall into the host halo, where they suffer tidal deformation and stripping.]
[The top left and right panels show DM structures inside the virial radius (Rvir) of the GRT cluster at z = 0 in the base simulation and the GRT simulation, respectively. The bottom left and right panels show the stellar structures in Rvir and 0.5Rvir of the GRT cluster, respectively. The structure of each panel is colored by DM and stellar surface mass density. The color scale for DM and stellar structures is shown next to the right panels.]
[[Structures of the GRT cluster at the epoch of the last major merger. In the central panel, the GRT protocluster is in the upper right and a group-sized halo companion is in the lower left. The left panel indicates the BGG, and the IGL and tidally stripped structure is in the right panel. The top panel indicates a UDG candidate galaxy near the center of the GRT protocluster.]
GRT-cluster Run
We perform the multi-resolution resimulation on six clusters, and follow their evolution until z = 0. The gravitational softening length for the high-resolution DM and stellar particles of ∼100 and ∼10 pc h−1 , respectively. The high-resolution particle mass for DM and star is 5.4 × 106 Me h−1 and 5.4 × 104 Me h−1 , respectively. The softening length and mass of low-resolution DM particles are the same as those of the low-resolution DM-only simulation. The mass of high-resolution DM (or star) particles is ∼200 (or 20,000) times smaller than that of the lowresolution DM particles. Although the presence of lowresolution DM particles could, in principle, artificially affect the evolution of the high-resolution stellar disk, the larger softening used for the low-resolution DM particles largely suppresses the scattering of high-resolution particles. Our measurements of the size evolution of infalling galaxies reveal that the level of artificial heating by low-resolution cluster DM particles is not significant for the studies of the ICL and BCG formation. More details can be found in Chun et al. 2023.
[The stellar distribution maps of the six GRT clusters at z = 0. The upper six panels show all the stellar components colored by stellar surface density. The lower six panels show V-band surface brightness (μV) of the ICL and BCG components, except for the satellites. The inner and outer gray dashed circular lines indicate the 0.1 and 0.5 Rvir of each cluster, respectively. Color bars indicate the surface density and V-band surface brightness.]
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