  We use Keck/DEIMOS spectroscopy to confirm the cluster membership of 16
ultra-diffuse galaxies (UDGs) in the Coma cluster, bringing the total number of
spectroscopically con- firmed UDGs to 24. We also identify a new cluster
background UDG. In this pilot study of Coma UDGs in velocity phase-space, we
find evidence that most present-day Coma UDGs have a recent infall epoch while
a few may be ancient infalls. These recent infall UDGs have higher absolute
relative line-of-sight velocities, bluer optical colors, and are smaller in
size, unlike the ancient infalls. The kinematics of the spectroscopically
confirmed Coma UDG sample is similar to that of the cluster late-type galaxy
population. Our velocity phase-space analysis suggests that present-day cluster
UDGs have a predominantly accretion origin from the field, acquire velocities
corresponding to the mass of the cluster at accretion as they are accelerated
towards the cluster center, and become redder and bigger as they experience the
various physical processes at work within the cluster.
