Flatiron Institute, Simons Foundation
The diverse history of counterrotating galaxies
Current and upcoming IFU and HI surveys will provide us with a wealth of kinematic information that could give clues to the evolutionary and environmental history of individual galaxies. Extreme kinematics like counter-rotation of gas or stars is particularly interesting as this can provide additional dynamical or evolutionary constraints. There is however no statistical prediction of the occurrence, properties and possible origin of counter-rotating galaxies within the concordance cosmological framework. I will present a study of these issues using the Illustris cosmological simulation. We predict the general occurrence and properties of counter-rotating galaxies over a large range in stellar mass. Additionally, we focus in detail on the evolutionary history of 5 disky sub-L* galaxies that show extremely clear gas disk-stellar disk counterrotation. These specific galaxies are selected as analogues to an observational sample of counter-rotating dwarf galaxies carried on with Keck. I will summarize the several mechanisms identified as origin of counter-rotation in low mass galaxies, and discuss possible links between counter-rotation and a galaxy’s evolutionary history.