Formation of misaligned second-generation discs through fly-by encounters

Observations reveal protoplanetary discs being perturbed by fly-by candidates. We simulate a scenario where an unbound perturber, i.e. a fly-by, undergoes an inclined grazing encounter, capturing material and forming a second-generation protoplanetary disc. We run N-body and three-dimensional hydrodynamical simulations of a parabolic fly-by grazing a particle disc and a gas-rich protoplanetary disc, respectively. In both our N-body and hydrodynamic simulations, we find that the captured, second-generation disc forms at a tilt twice the initial fly-by tilt. This relationship is robust to variations in the fly-by’s tilt, position angle, periastron, and mass. We extend this concept by also simulating the case where the fly-by has a disc of material prior to the encounter but we do not find the same trend. An inclined disc with respect to the primary disc around a misaligned fly-by is tilted by a few degrees, remaining close to its initial disc tilt. Therefore, if a disc is present around the fly-by before the encounter, the disc may not tilt up to twice the perturber tilt depending on the balance between the angular momentum of the circumsecondary disc and captured particles. In the case where the perturber has no initial disc, analysing the orientation of these second-generation discs can give information about the orbital properties of the fly-by encounter.