Dry mergers and the size evolution of early-type galaxies

TL;DR

This paper investigates the role of dry mergers in the size evolution of early-type galaxies, concluding that they contribute at most 45% of stellar mass assembly and require fine tuning, challenging their significance.

Contribution

It provides a quantitative analysis showing dry mergers are limited in their contribution to galaxy growth and highlights the need for precise conditions for their effectiveness.

Findings

Dry mergers contribute at most 45% of stellar mass in ETGs.

Extreme fine tuning is necessary for dry mergers to explain size evolution.

The local stellar mass-size relation constrains the role of dry mergers.

Abstract

Dry (i.e. dissipationless) merging has been proposed as the main driver of the observed size evolution of early-type galaxies (ETGs). The actual role of this mechanism is questioned by the tightness of the local stellar mass-size relation of ETGs. Combining this observed scaling law with simple merging models, which should bracket cosmologically motivated merging histories, we draw the following conclusions: 1) local massive ETGs can have assembled at most ~45% of their stellar mass via dry mergers; 2) extreme fine tuning is required for this to be the case.