# The Origin of Lopsided Satellite Galaxy Distribution in Galaxy Pairs

## TL;DR

This study investigates the origin of lopsided satellite galaxy distributions in galaxy pairs, revealing that such asymmetries weaken over time due to satellite interactions and are mainly caused by recently accreted, dynamically young satellites.

## Contribution

It identifies the evolutionary origin of lopsided satellite distributions in galaxy pairs and links the phenomenon to recent accretion events and satellite interactions.

## Key findings

- Lopsided distribution was stronger in the past and weakens towards present day.
- Interaction with the host pair weakens the lopsided signal over time.
- The current lopsided distribution is primarily driven by recently accreted satellites.

## Abstract

It is well known that satellite galaxies are not isotropically distributed among their host galaxies as suggested by most interpretations of the $\Lambda$CDM model. One type of anisotropy recently detected in the SDSS (and seen when examining the distribution of satellites in the Local Group and in the Centaurus group) is a tendency to be so-called "lopsided". Namely, in pairs of galaxies (like Andromeda and the Milky Way) the satellites are more likely to inhabit the region in between the pair, rather than on opposing sides. Although recent studies found a similar set up when comparing pairs of galaxies in $\Lambda$CDM simulations indicating that such a set up is not inconsistent with $\Lambda$CDM, the origin has yet to be explained. Here we examine the origin of such lopsided setups by first identifying such distributions in pairs of galaxies in numerical cosmological simulations, and then tracking back the orbital trajectories of satellites (which at $z=0$ display the effect). We report two main results: first, the lopsided distribution was stronger in the past and weakens towards $z=0$. Second, the weakening of the signal is due to the interaction of satellite galaxies with the pair. Finally, we show that the $z=0$ signal is driven primarily by satellites that are on first approach, who have yet to experience a "flyby". This suggests that the signal seen in the observations is also dominated by dynamically young accretion events.