On the Spin Bias of Satellite Galaxies in the Local Group-like Environment

TL;DR

This study uses the Millennium-II simulation to reveal a correlation between the spin parameters of subhalos and the mass ratio of main to submain halos in Local Group-like environments, indicating an intrinsic spin bias.

Contribution

It demonstrates that the spin bias of subhalos correlates with host halo mass ratios and persists across different redshifts, revealing an intrinsic property of LG-like systems.

Findings

Higher main-to-submain mass ratios lead to higher mean subhalo spin parameters.

The spin bias correlation exists at redshifts z=0, 0.5, and 1.

Subhalo spin bias is caused by anisotropic stress in LG-like environments.

Abstract

We utilize the Millennium-II simulation databases to study the spin bias of dark subhalos in the Local Group-like systems which have two prominent satellites with comparable masses. Selecting the group-size halos with total mass similar to that of the Local Group (LG) from the friends-of-friends halo catalog and locating their subhalos from the substructure catalog, we determine the most massive (main) and second to the most massive (submain) ones among the subhalos hosted by each selected halo. When the dimensionless spin parameter (lambda) of each subhalo is derived from its specific angular momentum and circular velocity at virial radius, a signal of correlation is detected between the spin parameters of the subhalos and the main-to-submain mass ratios of their host halos at z=0: The higher main-to-submain mass ratio a host halo has, the higher mean spin parameter its subhalos have. It is also found that the correlations exist even for the subhalo progenitors at z=0.5 and z=1. Our interpretation of this result is that the subhalo spin bias is not a transient effect but an intrinsic property of a LG-like system with higher main-to- submain mass ratio, caused by stronger anisotropic stress in the region. A cosmological implication of our result is also discussed.