The fate of disk galaxies in IllustrisTNG clusters

We study the stellar morphological evolution of disk galaxies within clusters in the TNG50 and TNG100 runs from the IllustrisTNG simulation suite. We select satellites of masses $10^{9.7}<=M_{*,z=0}/M_{sun}<=10^{11.6}$ residing in clusters of total masses $10^{14}<=M_{\text{200c,z=0}}/M_{sun}<10^{14.6}$ at z=0 and study those that were disks at accretion according to a kinematic morphology indicator (the circularity fraction). The galaxies' histories are traced from the time of accretion to $z=0$ and compared to a control sample of central galaxies mass-matched at the time of accretion. Most cluster disks become non-disky by z=0, in stark contrast with the control disks, of which a significant fraction remains disky over the same timescales. The transformation to non-disky morphologies is accompanied by gas removal and star formation quenching for both cluster and control galaxies. However, cluster disks that become non-disky by z=0 have lost dark matter (DM) mass and show little growth or a loss of stellar mass, whereas the corresponding control disks show significant growth in both components. Most cluster satellites change their morphologies on similar timescales regardless of stellar mass, in ~0.5-4 Gyr after accretion. Cluster disks that have had more numerous and closer pericentric passages show the largest change in morphology. Morphological change in both cluster and control disks requires the presence of a gravitational perturbation to drive stellar orbits to non-disky configurations, along with gas removal/heating to prevent replenishment of the disk through continued star-formation. For cluster disks, the perturbation is in the form of impulsive tidal shocking at pericentres and not tidal stripping of the outer disk stellar material, whereas for control disks, a combination of mergers and AGN feedback appears to be the key driving force behind morphological transformations.