2024/11/27 by Chanoul Seo, Seo, Chanoul, Suk-Jin Yoon +7
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #History and Developments in Astronomy #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2411.18040
openalex publication_date 2024/11/27 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The majority of satellite galaxies around the Milky Way (MW) show disk-like distributions (the disk of satellites; DoS), which is a small-scale problem of the ΛCDM cosmology. The conventional definition of the MW-like DoS is a satellite system with a minor-to-major axis ratio (c/a) lower than the MW's c/a value of 0.181. Here we question the validity of the c/a-based DoS rarity assessment and propose an alternative approach. How satellites are placed around a galaxy is dictated mainly by two factors: the distributions of satellites' orbital poles and distances from the host. Based on this premise, we construct the `satellite distribution generator' code and generate 105 `spatially and kinematically analogous systems (SKASs)' sharing these two factors. The SKAS can disclose the intrinsic, underlying c/a probability distribution function (PDF), from which a present-day c/a value is fortuitously determined. We find that the c/a PDF of the MW DoS defined by 11 classical satellites is quite broad (σc/a∼0.105), implying that a simple present-day c/a value, combined with its highly time-variable nature, cannot fully represent the degree of flatness. Moreover, based on the intrinsic c/a PDF, we re-evaluate the rarity of the MW DoS by comparing it with IllustrisTNG50-1 host-satellite systems and find that even with the new measure, the MW DoS remains rare (0.00∼3.40%). We show that the reason behind the rareness is that both orbital poles and distances of the 11 MW satellites are far more plane-friendly than those of simulated host-satellite systems, challenging the current structure and galaxy formation model.