Mass Loss From Planetary Nebulae in Elliptical Galaxies

TL;DR

This study uses hydrodynamic simulations to explore how planetary nebula ejecta interacts with hot gas in elliptical galaxies, revealing that much of the ejecta remains cooler and may not fully mix into the hot ambient medium.

Contribution

It provides new insights into the thermal evolution of planetary nebula ejecta in elliptical galaxies, highlighting differences from continuous stellar mass loss.

Findings

Approximately half of the ejecta separates from the flow.

Most of the separated ejecta remains below 1E5 K.

A significant fraction of ejecta may not heat up to ambient temperatures.

Abstract

Early-type galaxies possess a dilute hot (2-10E6 K) gas that is probably the thermalized ejecta of the mass loss from evolving stars. We investigate the processes by which the mass loss from orbiting stars interacts with the stationary hot gas for the case of the mass ejected in a planetary nebula event. Numerical hydrodynamic simulations show that at first, the ejecta expands nearly symmetrically, with an upstream bow shock in the hot ambient gas. At later times, the flow past the ejecta creates fluid instabilities that cause about half of the ejecta to separate and the other half to flow more slowly downstream in a narrow wake. When radiative cooling is included, most of the material in the wake (>80%) remains below 1E5 K while the separated ejecta is hotter (1E5-1E6 K). The separated ejecta is still less than one-quarter the temperature of the ambient medium and the only way it will reach the temperature of the ambient medium is through turbulent mixing (after the material has left the grid). These calculations suggest that a significant fraction of the planetary nebula ejecta may not become part of the hot ambient material. This is in contrast to our previous calculations for continuous mass loss from giant stars in which most of the mass loss became hot gas. We speculate that detectable OVI emission may be produced, but more sophisticated calculations will be required to determine the emission spectrum and to better define the fraction of cooled material.