as Shell A in Fig. 8). A comparison with the optical image clearly shows that these two optical shells are surrounded by molecular material. Thus, the CO emission distribution confirms the presence of PDRs at the interface between the ionized and molecular gases.

A comparison of the distribution of the massive dense cores found by @russ10 with Shell A shows that 65% out of the $\sim$ 70 massive cores are projected onto the CO shell. Velocities of the most massive cores are in the range –2.0 to –4.3 , in agreement with the velocity of Shell A. This indicates that the molecular counterpart of G353.12+0.86 is a region of active star formation that has probably been triggered by the expansion of G353.12+0.86 (see for example @hes05).

The dust column that separates the optical shells can be identified as an elephant trunk pointing towards the centre of G353.12+0.86. The dust cloud coincides in position with a CO cloud having velocities in the range \[$-$12.5,$-$7.5\]  (named cloud B in Fig. 8). However, the existence of molecular gas linked to this dust cloud with velocities  can not be ruled out because of the poor angular resolution of the CO data in comparison with 