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 } \sim + 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 } \sim + 80 { km } { s } ^ { -1 } seen in ^ { 12 } CO ( J =1–0 and J =3–2 ) data , as well as the high-velocity expanding H i shells up to V _ { LSR } \sim + 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 \sim 4.1 kpc based on the H i self-absorption method , which leads to a physical radius of 29.0 pc for the \sim ( 0.7–2.0 ) \times 10 ^ { 5 } years old remnant with an expansion velocity of \mbox { \raisebox { 2.15 pt } { $ > $ } \raisebox { -2.15 pt } { $ \sim$ } } 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 .