Black Hole Boundary-Layer Atlas: Structural Motifs in Nearby Galaxy Systems

Black Hole Boundary-Layer Atlas: Structural Motifs in Nearby Galaxy Systems presents a comparative observational framework for identifying recurring boundary-layer structure across nearby galaxy groups. The atlas focuses on black-hole-hosting dwarfs as key markers of galactic boundaries and documents a consistent set of motifs across diverse environments, including harmonic pairs, mass-ratio ladders, chain and bridge structures, outer-boundary symmetry, and terminal boundary states. Across systems ranging from sparse associations to richer multi-galaxy environments, these motifs recur with notable regularity, suggesting shared structural organization at galaxy-system edges. The atlas establishes a reproducible method based on estimating black hole masses from observational indicators, normalizing object positions to characteristic group radii, identifying structural motifs through consistent spacing and mass-ratio thresholds, and evaluating debris, stream, and terminal-boundary conditions. This framework is applied uniformly across all systems in the study, allowing direct comparison between galaxy groups with different morphologies, densities, and interaction histories. The work is organized as a system-by-system observational atlas. Early cases such as Centaurus A, IC 342 / Maffei, the Local Group edge, M31, and M81 illustrate how the same motif framework appears in environments with different central-mass configurations, visibility conditions, and dynamical complexity. In each case, the atlas tracks the transition from disturbed interiors to quieter outer regions, emphasizing the structural role of dwarf galaxies that occupy normalized boundary and terminal positions. Rather than proposing a finished theoretical model, this atlas provides a data-driven observational foundation for future work on galaxy boundary architecture, halo structure, and large-scale pattern formation. Its primary contribution is to define a stable comparative vocabulary for recognizing and testing structural regularities in the boundary layers of nearby galaxy systems.