  We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
of the CO ($J$=2--1) line emission from the protoplanetary disk around T-Tauri
star SU Aurigae (hereafter SU Aur). Previous observations in optical and near
infrared wavelengths find a unique structure in SU Aur. One of the highlights
of the observational results is that an extended tail-like structure is
associated with the disk, indicating mass transfer from or into the disk. Here
we report the discovery of the counterpart of the tail-like structure in CO gas
extending more than 1000 au long. Based on geometric and kinematic
perspectives, both of the disk and the tail-like structure components
physically connect to each other. Several theoretical studies predicted the
observed tail-like structure via the following possible scenarios, 1) a gaseous
stream from the molecular cloud remnant, 2) collision with a (sub)stellar
intruder or a gaseous blob from the ambient cloud, and 3) ejection of a
planetary or brown dwarf mass object due to gravitational instability via
multi-body gravitational interaction. Since the tail-like structures associated
with the SU Aur disk is a new example following RW Aurigae, some disks may
experience the internal or external interaction and drastically lose mass
during disk evolution.
