# A New Class of X-Ray Tails of Early-Type Galaxies and Subclusters in Galaxy Clusters - Slingshot Tails vs Ram Pressure Stripped Tails

## TL;DR

This paper introduces a new class of gas tails called slingshot tails in galaxy clusters, which form during subhalo orbital apocenter and can mislead interpretations based on tail direction, challenging traditional ram pressure stripping assumptions.

## Contribution

The paper identifies and characterizes slingshot tails, revealing their formation mechanism, morphology, and how they differ from classic ram pressure stripped tails in galaxy clusters.

## Key findings

- Slingshot tails form at orbital apocenter and can point opposite to the subhalo's motion.
- Traditional RPS interpretations can lead to incorrect conclusions about subhalo dynamics.
- Three literature examples are identified as slingshot tails, not RPS tails.

## Abstract

We show that there is a new class of gas tails - slingshot tails - which form as a subhalo (i.e. a subcluster or early-type cluster galaxy) moves away from the cluster center towards the apocenter of its orbit. These tails can point perpendicular or even opposite to the subhalo direction of motion, not tracing the recent orbital path. Thus, the observed tail direction can be misleading, and we caution against naive conclusions regarding the subhalo's direction of motion based on the tail direction. A head-tail morphology of a galaxy's or subcluster's gaseous atmosphere is usually attributed to ram pressure stripping and the widely applied conclusion is that gas stripped tail traces the most recent orbit. However, during the slingshot tail stage, the subhalo is not being ram pressure stripped (RPS) and the tail is shaped by tidal forces more than just the ram pressure. Thus, applying a classic RPS scenario to a slingshot tail leads not only to an incorrect conclusion regarding the direction of motion, but also to incorrect conclusions in regard to the subhalo velocity, expected locations of shear flows, instabilities and mixing. We describe the genesis and morphology of slingshot tails using data from binary cluster merger simulations, discuss their observable features and how to distinguish them from classic RPS tails. We identify three examples from the literature that are not RPS tails but slingshot tails and discuss other potential candidates.