tokens: are able to identify galaxies , which have internal and external properties different from dark matter subhalos in several respects. Stellar components tend to be more compact than their dark matter counterparts, and thus better survive the strong background tidal force exerted by their host halo. The background potential, however, is largely governed by the dark matter component. Sometimes, satellite galaxies may even lose their associated dark matter component through tidal disruption as they orbit within the group. In our search for galaxies, we thus start from the stellar distribution, which is then used as a seed to explore the distribution of the other particle species. We first identify the N s nearest star particle neighbors of each star particle and measure local densities using the W 4 smoothed particle hydrodynamics (SPH) density kernel (Monaghan Lattanzio 1985 ). We build a neighborhood network using chains of N n -nearest neighbors at each particle position. This means that all particles have their own neighboring connections. This coordinate-free method suppresses the ambiguities that arise in building the density field, and it reduces the number of parameters required by the galaxy-finding algorithm. Second, we search for the peaks in the stellar mass density field at each particle position. These peaks are local maxima with respect to their own N n neighbors. To alleviate the identification of spurious local peaks due to Poisson noise, we adopt two approaches. One approach is to merge multiple peaks if their distance is less than l merge . The other approach is to set both the minimum number of stars and the minimum stellar mass in the core region. Here, a core region is a volume identified by progressively lowering the density threshold down to the point where the isodensity surface encloses another peak. This is similar to the watershed method. At this point, particles within the isodensity surface are considered to belong to a galaxy candidate centered on the enclosed peak. Third, after extracting core particles related to a density peak, we apply density cuts to group the remaining (noncore) particles utilizing the watershed method. Around each density core, we search for noncore particles whose densities are between the i th and i + 1th density thresholds. We gather those particles to build a “shell” group. By definition, a shell group should surround other density groups. Accordingly, all particles are split into core and shell groups. Finally, to complete the membership decision, we check the tidal boundary of each galaxy candidate, as well as the total energy of particles within the boundary. Even though a particle may be bound to a galaxy, it is not considered a member unless it is within the tidal radius. Figure 6 shows the most massive halo in HR5 identified using the variable FoF approach at z = 0.76. Even with varying particle mass, the derived distributions of dark matter (top left) and gas (bottom left) are
ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model I-Model I-Model I-Model B-Model B-Model I-Model B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O B-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O