Monday

Minor mergers produce faint tidal features, invisible in current surveys. However, future surveys e.g. LSST, EUCLID, JWST etc, will open up a new regime of wide, low surface brightness imaging deep enough to allow these faint tidal features to be studied in large numbers for the first time. While past work has suggested that the bulk of the morphological transformation of galaxies may have taken place as a result of major mergers i.e. near-equal mass mergers, recent observational work has shown that newborn spheroids often do not exhibit the tidal features expected from major mergers. This raises the possibility that other processes may be chiefly responsible for driving the bulk of the morphological transformation over cosmic time, the two obvious candidates being minor mergers and/or smooth accretion.

We use a cosmological simulation (Horizon-AGN) to explore the role of major and minor mergers in driving morphological transformations. We show that, while the morphological mix observed in the local universe cannot be reproduced without also appealing to major mergers, minor mergers contribute significantly to the process of morphological transformation. Additionally, we find that accretion from the environment and very low mass ratio mergers (less than 1:15) also have an important role to play in gradual morphological evolution of lower mass galaxies (i.e. less than 5e10 solar masses) and in spinning up higher mass galaxies.