A Tail Structure Associated with a Protoplanetary Disk around SU Aurigae

We present Atacama Large Millimeter/submillimeter Array observations of the CO (J = 2 - 1) line emission from a 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 multibody gravitational interaction. Since the tail-like structures associated with the SU Aur disk are a new example following RW Aurigae, some disks may experience the internal or external interaction and drastically lose mass during disk evolution.