Shape and kinematics of elliptical galaxies: evolution due to merging at z < 1.5

TL;DR

This study uses hydrodynamic simulations to analyze how elliptical galaxies evolve in shape and kinematics from redshift 1.5 to 0, primarily due to dry mergers that make them rounder and more dispersion-supported.

Contribution

It provides a detailed simulation-based analysis of elliptical galaxy evolution, highlighting the role of dry mergers in changing their shape and kinematic support over time.

Findings

Elliptical galaxies become rounder and more dispersion-supported at z=0.

Major dry mergers are the primary driver of shape and kinematic evolution.

Some mergers involve high angular momentum, increasing rotational support.

Abstract

Aims:In this study we investigate the evolution of shape and kinematics of elliptical galaxies in a cosmological framework. Methods: We use a set of hydrodynamic, self-consistent simulations operating in the context of a concordance cosmological model where relaxed elliptical-like objects (ELOs) were identified at redshifts z=0, z=0.5, z=1 and z=1.5. Results: The population of elliptical systems analysed here present a systematic change through time, i.e. evolution, by becoming rounder in general at z=0 and, at the same time more velocity dispersion supported. This is found to be primarily due to major dry mergers where only a modest amount of angular momentum is involved into the merger event. Despite the general trend, in a significant amount of cases the merger event involves a higher specific angular momentum, which in general causes the system to acquire a higher rotational support and/or a more oblate shape. These evolutionary patterns are still present when we study our systems in projection, mimicking real observations, and thus they should become apparent in future observations.