Galaxy Zoo: Multi-Mergers and the Millennium Simulation

TL;DR

This study catalogs multi-mergers from Galaxy Zoo data, compares their frequency and properties with Millennium Simulation predictions, and finds good agreement, supporting the models' accuracy in representing galaxy mergers.

Contribution

It provides the first observational catalog of multi-mergers at low redshift and compares their properties with semi-analytical models from the Millennium Simulation.

Findings

Multi-merger fraction is at least 100 times less than binary mergers.

Multi-mergers are associated with elliptical galaxy properties.

Observations agree with Millennium Simulation predictions.

Abstract

We present a catalogue of 39 multiple-mergers found using the mergers catalogue of the Galaxy Zoo project for $z<0.1$ and compare them to corresponding semi-analytical galaxies from the Millennium Simulation. We estimate the (volume-limited) multi-merger fraction of the local Universe using our sample and find it to be at least two orders of magnitude less than binary-mergers - in good agreement with the simulations (especially the Munich group). We then investigate the properties of galaxies in binary- and multi-mergers (morphologies, colours, stellar masses and environment) and compare these results with those predicted by the semi-analytical galaxies. We find that multi-mergers favour galaxies with properties typical of elliptical morphologies and that this is in qualitative agreement with the models. Studies of multi-mergers thus provide an independent (and largely corroborating) test of the Millennium semi-analytical models.