On the dependence of galaxy morphologies on galaxy mergers

TL;DR

This study examines how galaxy mergers influence galaxy morphology, comparing different modeling approaches and observational data to understand spheroid formation and the limitations posed by current uncertainties.

Contribution

It introduces new prescriptions for merger-driven bulge formation based on hydrodynamical simulations and compares these with standard models and observations.

Findings

New merger prescriptions reduce bulge formation efficiency.

Uncertainties in observational data limit model constraints.

Main discrepancy lies in the distribution of galaxy types by stellar mass.

Abstract

The distribution of galaxy morphological types is a key test for models of galaxy formation and evolution, providing strong constraints on the relative contribution of different physical processes responsible for the growth of the spheroidal components. In this paper, we make use of a suite of semi-analytic models to study the efficiency of galaxy mergers in disrupting galaxy discs and building galaxy bulges. In particular, we compare standard prescriptions usually adopted in semi-analytic models, with new prescriptions proposed by Kannan et al., based on results from high-resolution hydrodynamical simulations, and we show that these new implementations reduce the efficiency of bulge formation through mergers. In addition, we compare our model results with a variety of observational measurements of the fraction of spheroid-dominated galaxies as a function of stellar and halo mass, showing that the present uncertainties in the data represent an important limitation to our understanding of spheroid formation. Our results indicate that the main tension between theoretical models and observations does not stem from the survival of purely disc structures (i.e. bulgeless galaxies), rather from the distribution of galaxies of different morphological types, as a function of their stellar mass.