Is HESS J1912+101 Associated with an Old Supernova Remnant?

HESS J1912+101 is a shell-like TeV source that has no clear counterpart in multiwavelength. Using CO and H I data, we reveal that V _LSR ∼ +60 km s^-1 molecular clouds (MCs), together with shocked molecular gas and high-velocity neutral atomic shells, are concentrated toward HESS J1912+101. The prominent wing profiles up to V _LSR ∼ +80 km s^-1 seen in ¹²CO (J = 1-0 and J = 3-2) data, as well as the high-velocity expanding H I shells up to V _LSR ∼ +100 km s^-1, exhibit striking redshifted-broadening relative to the quiescent gas. These features provide compelling evidences for large-scale perturbation in the region. We argue that the shocked MCs and the high-velocity H I shells may originate from an old supernova remnant (SNR). The distance to the SNR is estimated to be ∼4.1 kpc based on the H I self-absorption method, which leads to a physical radius of 29.0 pc for the ∼(0.7-2.0) × 10⁵ years old remnant with an expansion velocity of ≳40 km s^-1. The +60 km s^-1 MCs and the disturbed gas are indeed found to coincide with the bright TeV emission, supporting the physical association between them. Naturally, the shell-like TeV emission comes from the decay of neutral pions produced by interactions between the accelerated hadrons from the SNR and the surrounding high-density molecular gas.