The diverse history of counter-rotating galaxies Tjitske K. Starkenburg1, Laura V. Sales2, Shy Genel1,3, Christina Manzano-King2, Gabriela Canalizo2 1Center for Computational Astrophysics, the Flatiron Institute, 2University of California Riverside, 3Columbia University Introduction Galaxies containing significant counter-rotating components are particularly interesting as it can provide additional dynamical constraints (i.e. polar ring galaxies: Schweizer et al 1983; Athanassoula & Bosma 1985; Sackett & Sparke 1990) and hold clues to evolutionary history and past environment (e.g. Cappellari 2016). However, while isolated simulations have shown that mergers and smooth accretion onto gas-poor galaxies can form galaxies with counterrotating components (Thakar & Ryden 1996, Puerari & Pfenniger 2001, Algorry et al. 2014) the statistical occurrence and completeness of these origins are not clear. Moreover, there is no general prediction of the occurrence and properties of these galaxies within the cosmological framework. This poster is a first step towards a study of these issues using the Illustris cosmological simulation (Vogelsberger et al. 2014; Genel et al. 2014). We focus on the evolutionary history of 1 disky sub-L* galaxy that shows extremely clear gas disk - stellar disk counterrotation. This specific galaxies is selected as an analogue to an observational sample of counterroting dwarf galaxies carried on with Keck. Abstract Galaxies with counter-rotating gas or stars are particularly interesting. Their distinct kinematical components can provide additional dynamical constraints and possible clues to evolutionary history and past environment. These intriguing systems have since long been observed, but have rarely been studied collectively. We present a study of their occurrence, properties, and evolutionary history using the Illustris cosmological simulation. In this poster we focus in detail on the surprising evolutionary history of 1 disky sub-L* galaxy that shows clear gas disk - stellar disk counterrotation. The counter-rotation in this system is due to the system being a splashback satellite that re-accretes material. We thus show that the origin of significant counter-rotation in low mass galaxies can be diverse and unexpected. Figure 1.1: Face-on (top four panels) and edge-on (bottom four panels) of the stellar disk (left) and the gaseous disk (right) defined by the total angular momentum of the stars within 2 stellar half mass radii, where the top and third row show the projected surface density and the second and bottom row show the line-of- sight velocity. The bottom row shows clearly the opposite direction of rotation for the stellar disk and the (inclined) gaseous disk. Section 1: a counterrotating galaxy The galaxy used as an example for this poster shows clear counterrotation. The angle between the total angular momentum of the stars and the gas disks is 131 degrees, and the stellar and gaseous projected surface densities and velocities (face-on and edge-on with respect to the stellar disk) in Figure 1.1 show that the complete gas disk actually is inclined with respect to the stellar disk (by 131 degrees). Even though the stellar disk is very thick, the rotation in the stellar disk is significant. Figure 1.2 shows simple mock observational rotation curves (red: stars; blue: gas), measured assuming a slit that includes all gas and stars along the line-of- sight, with the galaxy perfectly edge-on, within a vertical distance of 1 kpc above and below the plane of the stellar disk. The points and error bars indicate the mean and standard deviation of all material along the line-of-sight. The gas and stellar velocities in this plane are similar in magnitude but exactly opposite in sign. Figure 2.1: Evolution of the angle of the total angular momentum vector of the stars and the gas within the galaxy and the gas in the halo with respect to the total angular momentum vector of the stars at the present day. The direc