# Orbital distribution of infalling satellite halos across cosmic time

13 Aug 2020  ·  Li Zhao-Zhou, Zhao Dong-Hai, Jing Y. P., Han Jiaxin, Dong Fu-Yu ·

The initial orbits of infalling subhalos largely determine the subsequent evolution of the subhalos and satellite galaxies therein and shed light on the assembly of their hosts. Using a large set of cosmological simulations of various resolutions, we quantify the orbital distribution of subhalos at infall time and its mass and redshift dependence in a large dynamic range... We further provide a unified and accurate model validated across cosmic time, which can serve as the initial condition for semi-analytic models. We find that the infall velocity $v$ follows a universal distribution peaked near the host virial velocity $V_{\mathrm{h}}$ for any subhalo mass or redshift, while the infall orbit is most radially biased when $v\sim V_{\mathrm{h}}$. Moreover, subhalos that have a higher host mass or a higher sub-to-host ratio tend to move along a more radial direction with a relatively smaller angular momentum than their low host mass or low sub-to-host ratio counterparts, though they share the same normalized orbital energy. These relations are nearly independent of the redshift and very likely the cosmology when using the density peak height as the proxy for host halo mass. The above trends are consistent with the scenario where the dynamical environment is relatively colder for more massive structures because their own gravity is more likely to dominate the local potentials. In addition, the external tidal fields seem to affect more the orbit direction rather than the amplitude of the velocity. read more

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Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies