Bullet Shooting Cloud–Cloud Collision in MIR Bubble N65

Abstract We report that the formation of the twin-bubble system N65 and N65bis may be caused by the cloud–cloud collision (CCC) from the Bullet Nebula. The blueshifted 13 CO gas component (N65a [47, 55] km s −1 ) is associated with the twin-bubble system, while the redshifted 13 CO gas component (N65b [55, 62] km s −1 ) is linked to the Bullet Nebula. The distinct signatures of CCC, such as the bridge feature, the U-shaped cavity, and the complementary distribution with displacement, are found between N65a and N65b. The collision timescale is estimated to be 1.15–2.0 Myr, which is consistent with the dynamical ages of the two H ii regions in N65a (0.73 Myr for N65bis and 1.19 Myr for N65, respectively), indicating their CCC-related origin. A total of 354 young stellar objects (YSOs) are found, which are clustered into eight minimum spanning tree groups. The distribution of M1 (at the post-frontal edge) and M2, M3, M4 (at the pre-frontal edge) suggests that the CCC triggers star formation along the collision path of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>b</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> <mml:mn>35</mml:mn> </mml:math> , with younger YSOs present at the pre-frontal edge. Therefore, the bipolar morphology of the twin-bubble system can be interpreted by the collision of N65a and N65b along <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>b</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> <mml:mn>35</mml:mn> </mml:math> about 2 Myr ago.