Effects of hot halo gas on the star formation and mass transfer during distant galaxy-galaxy encounters

TL;DR

This study uses simulations to show that hot halo gas significantly influences star formation and mass transfer during distant galaxy encounters, affecting gas dynamics and accretion processes.

Contribution

It demonstrates the hydrodynamic effects of hot halo gas on star formation and mass transfer during galaxy encounters, a novel insight into galaxy interaction dynamics.

Findings

Hot halo gas induces shock formation and star formation near the galaxy closest approach.

Presence of hot gas halos alters the cold gas bridge development and star accretion.

Hot halo gas can ionize and hinder cold gas transfer between galaxies.

Abstract

We use $N$-body/smoothed particle hydrodynamics simulations of encounters between an early-type galaxy (ETG) and a late-type galaxy (LTG) to study the effects of hot halo gas on the evolution for a case with the mass ratio of the ETG to LTG of 2:1 and the closest approach distance of $\sim$100 kpc. We find that the dynamics of the cold disk gas in the tidal bridge and the amount of the newly formed stars depend strongly on the existence of a gas halo. In the run of interacting galaxies not having a hot gas halo, the gas and stars accreted into the ETG do not include newly formed stars. However, in the run using the ETG with a gas halo and the LTG without a gas halo, a shock forms along the disk gas tidal bridge and induces star formation near the closest approach. The shock front is parallel to a channel along which the cold gas flows toward the center of the ETG. As a result, the ETG can accrete star-forming cold gas and newly born stars at and near its center. When both galaxies have hot gas halos, a shock is formed between the two gas halos somewhat before the closest approach. The shock hinders the growth of the cold gas bridge to the ETG and also ionizes it. Only some of the disk stars transfer through the stellar bridge. We conclude that the hot halo gas can give significant hydrodynamic effects during distant encounters.