We develop a new model within which the radius-dependent transition of the subhalo inner spins with respect to the cosmic web and the variation of the transition threshold radius ($r_{\rm th}$) with subhalo mass ($M_{\rm vir}$), smoothing scale ($r_{f}$), and redshift ($z$) can be coherently explained. The key tenet of this model is that the competition between the pressure effect of the inner mass and the compression effect of the local tidal field determines which principal direction of the tidal field the inner spins are aligned with. If the former predominates, then only the tidal torques turn on, resulting in the alignments of the inner spins with the intermediate principal axes of the tidal field. Otherwise, the subhalo spins acquire a tendency to be aligned with the shortest axes of the subhalo shapes, which is in the major principal directions of the tidal field. Quantifying the two effects in terms of the densities, we make a purely analytical prediction for $r_{\rm th}(M_{\rm vir}, z, r_{f})$. Testing this model against the numerical results from a high-resolution dark matter only N-body simulation in the redshift range of $0\le z\le 3$ on the galactic mass scale of $11.8\le \log[M_{\rm vir}/(h^{-1}M_{\odot})]\le 12.6$ for two different cases of $r_{f}/(h^{-1}{\rm Mpc})=0.5$ and $1$, we find excellent agreements of the model predictions with the numerical results. It is also shown that this model naturally predicts the alignments between the inner spins of the present subhalos with the principal axes of the high-$z$ tidal field at the progenitors' locations.
Symfind: Addressing the Fragility of Subhalo Finders and Revealing the Durability of Subhalos
SLAC National Accelerator Laboratory（SLAC国家加速器实验室）；Department of Physics, Stanford University（斯坦福大学物理系）；Carnegie Observatories（卡内基观测站）；Department of Astronomy, University of Maryland, College Park（马里兰大学帕克分校天文学系）
The BUFFALO Survey : The Subhalo Mass Function for Abell 2744 with Strong+Weak Gravitational Lensing
Durham University（杜伦大学）；University of KwaZulu-Natal（夸祖鲁-纳塔尔大学）；STAR Institute（STAR研究所）；University of Hertfordshire（赫特福德大学）；Carnegie Observatories（卡内基天文台）
Filament-Arm Node Systems (FANS): A new probe of the winding and chirality of the cosmic web
Center for Cosmology and Computational Astrophysics, Institute for Advanced Study in Physics, Zhejiang University（浙江大学高等物理研究院宇宙学与计算天体物理学中心）；Institute of Astronomy, School of Physics, Zhejiang University（浙江大学物理学院天文学研究所）
