Energy evolution in the progenitor of galaxy shells: a semi-analytical model

TL;DR

This paper presents a semi-analytical model to understand how energy and angular momentum evolve in the progenitor dwarf galaxy of stellar shells, crucial for predicting shell structures in elliptical galaxies.

Contribution

The model incorporates the effects of self-gravity on energy and angular momentum changes during infall, improving shell formation predictions.

Findings

Self-gravity significantly broadens the initial energy distribution.

Energy changes are crucial for shell morphology.

Accurate disruption energy range predicts observable shells.

Abstract

The stellar shells surrounding an elliptical galaxy, as remnants of a dwarf galaxy disrupted during merging, reveal the distribution of energy and angular momentum of the progenitor dwarf galaxy. We develop a semi-analytical model to describe the changes of energy $\Delta E_i$ and angular momentum $\Delta Lz_i$ for particles during the first infall. We show that these changes, induced by the self-gravity of the progenitor, are important in broadening the initial energy distribution of the Plummer or Hernquist progenitor model. Consequently, these changes are crucial in shaping the shells. In the free fall stage following the disintegration of the progenitor potential, particles are no longer bound by self-gravity but move within the gravitational potential of the target galaxy. We investigate the relationship between the radial period and the energy of particles undergoing radial motion. We show that an accurate model of the energy range of the dwarf galaxy at disruption is essential to predict the number of observable shells.