How frequent do spiral discs reform after mergers?
Our work on "The diversity of assembly histories leading to disc galaxy formation in a LambdaCDM model" has been published (Font et al 2017, PASA).
It is well known that disc galaxies often experience mergers with other galaxies and that these mergers are massive enough to destroy the discs. It is also known that discs can reform sometime afterwards, if there is enough gas to re-fuel star formation. What is less known, however, is how frequent is this process in the cosmological context, in order to explain the ubiquity of spiral discs in the Universe. In this study, we make a statistical analysis of this process using cosmological simulations. What we find is that the majority of present-day disc galaxies have formed after massive mergers and only a small fraction formed quiescently. This reconciles the observed ubiquity of disc galaxies in the real Universe with the high number of disc-destroying mergers predicted in the LCDM model.
This pie-chart shows that more than half of present-day galaxies (54%) have formed after mergers and are discs today. In comparison, only 20% of all galaxies today are disc galaxies that formed quiescently:
