Generation of rotationally dominated galaxies by mergers of pressure-supported progenitors

TL;DR

This study uses numerical simulations to show that major mergers of pressure-supported, non-rotating galaxies can produce elliptical-like galaxies with significant rotational support, depending on initial conditions and orbital parameters.

Contribution

It demonstrates that mergers of pressure-supported progenitors can generate rotationally dominated galaxies, highlighting the role of angular momentum transfer and initial galaxy properties.

Findings

Outer regions acquire angular momentum first.

Both baryonic and dark matter components gain angular momentum.

The initial density and orbital angular momentum influence the remnant's rotation.

Abstract

Through the analysis of a set of numerical simulations of major mergers between initially non-rotating, pressure supported progenitor galaxies with a range of central mass concentrations, we have shown that: (1) it is possible to generate elliptical-like galaxies, with v/sigma > 1 outside one effective radius, as a result of the conversion of orbital- into internal-angular momentum; (2) the outer regions acquire part of the angular momentum first; (3) both the baryonic and the dark matter components of the remnant galaxy acquire part of the angular momentum, the relative fractions depend on the initial concentration of the merging galaxies. For this conversion to occur the initial baryonic component must be sufficiently dense and/or the encounter should take place on a orbit with high angular momentum. Systems with these hybrid properties have been recently observed through a combination of stellar absorption lines and planetary nebulae for kinematic studies of early-type galaxies. Our results are in qualitative agreement with such observations and demonstrate that even mergers composed of non-rotating, pressure-supported progenitor galaxies can produce early-type galaxies with significant rotation at large radii.