We report results of molecular line observations carried out toward a massive dense core in the Cyg OB 7 molecular cloud .
The core has an extraordinarily large mass ( \sim 1.1 \times 10 ^ { 4 } M _ { \odot } ) and size ( \sim 2 \times 5 pc ^ { 2 } ) , but there is no massive young star forming therein .
We observed this core in various molecular lines such as C ^ { 18 } O ( J = 1 - 0 ) using the 45m telescope at Nobeyama Radio Observatory .
We find that the core has an elongated morphology consisting of several filaments and core-like structures .
The filaments are massive ( 10 ^ { 2 } -10 ^ { 3 } M _ { \odot } ) , and they are apparently colliding against each other .
Some candidates of YSOs are distributed around their intersection , suggesting that the collisions of the filaments may have influenced on their formation .
To understand the formation and evolution of such colliding filaments , we performed numerical simulations using the adaptive mesh refinement ( AMR ) technique adopting the observed core parameters ( e.g. , the mass and size ) as the initial conditions .
Results indicate that the filaments are formed as seen in other earlier simulations for small cores in literature , but we could not reproduce the collisions of the filaments simply by assuming the large initial mass and size .
We find that the collisions of the filaments occur only when there is a large velocity gradient in the initial core in a sense to compress it .
We suggest that the observed core was actually compressed by an external effect , e.g. , shocks of nearby supernova remnants including HB21 which has been suggested to be interacting with the Cyg OB 7 molecular cloud .