Kinematic patterns of the enriched gas phase in the Local Group {\sc Hestia} simulations

TL;DR

This study uses high-resolution simulations to analyze the kinematic patterns of gas in the Local Group, revealing a velocity dipole consistent with observations and highlighting differences among ionic species.

Contribution

It provides the first detailed simulation-based analysis of ionic gas kinematics in the Local Group, matching observed velocity patterns and exploring ion-specific behaviors.

Findings

Detection of a velocity dipole in gas outside the Milky Way halo.

Higher oxygen ions trace hot gas and show clearer dipole patterns.

Inner regions of the Local Group exhibit higher pressures.

Abstract

Observations of intergalactic absorbers in the Local Group suggest the existence of a velocity dipole in the general barycentre--antibarycentre direction which can be interpreted as evidence of a general flow of material towards the group's centre of mass. In this work, we study the kinematics of gas in the Local Group using one of the high-resolution realisations of the {\sc Hestia} simulations with a particular focus on the evidence left by different ionic species. Our simulation includes the correct cosmography for a region similar to the Local Group and a relative radial velocity between the candidate Milky Way and Andromeda galaxies consistent with the observed one. We examine the distribution and kinematics of six ionic species (H\,{\sc i}, C\,{\sc iv}, Si\,{\sc iii}, O\,{\sc vi}, O\,{\sc vii} and O\,{\sc viii}) and their imprints on synthetic sky maps constructed from the reference frames commonly used by observers. Our results indicate the presence of such a dipole for gas outside the Milky Way halo, favouring a paradigm in which the Milky Way is moving against the gas in the direction of the barycentre, while moving away from it in the opposite direction. This pattern is clearer for the higher oxygen ions, which preferentially trace hot gas. On the other hand, we observe a slight asymmetry in the pressure profiles in both directions, indicating higher pressures in the inner regions of the Local Group.