Local interstellar medium kinematics towards the Southern Coalsack and Chamaeleon-Musca dark clouds

We present the results of a spectroscopic programme aiming to investigate the kinematics of the local interstellar medium components towards the Southern Coalsack and Chamaeleon-Musca dark clouds. The analysis is based upon high-resolution (Rapproximate to60000) spectra of the interstellar Na I D absorption lines towards 63 B-type stars (dless than or equal to500 pc) selected to cover these clouds and the connecting area defined by the Galactic coordinates: 308degreesgreater than or equal tolgreater than or equal to294degrees and -22degreesgreater than or equal tobgreater than or equal to5degrees. The radial velocities, column densities, velocity dispersions, colour excess and photometric distances to the stars are used to understand the kinematics and distribution of the interstellar cloud components. The analysis indicates that the interstellar gas is distributed in two extended sheet-like structures permeating the whole area, one at dless than or equal to60 pc and another around 120-150 pc from the Sun. The nearby feature is approaching the local standard of rest with an average radial velocity of -7 km s(-1), has low average column density log N(Na1)approximate to11.2 cm(-2) and velocity dispersion bapproximate to5 km s(-1). The more distant feature has column densities between 12.3less than or equal tolog N(Na1)less than or equal to13.2, average velocity dispersion bapproximate to2.5 km s(-1) and seems associated with the dust sheet observed towards the Coalsack, Musca and Chamaeleon direction. Its velocity is centred around 0 km s(-1), but there is a trend for increasing from -3 km s(-1) near b=1degrees to 3 km s(-1) near b=-18degrees. The nearby low column density feature indicates a general outflow from the Sco-Cen association, in agreement with several independent lines of data in the general searched direction. The dust and gas feature around 120-150 pc seem to be part of an extended large-scale feature of similar kinematic properties, supposedly identified with the interaction zone of the Local and Loop I Bubbles. Assuming that the interface and the ring-like volume of dense neutral matter that would have been formed during the collision of the two bubbles have similar properties, our results suggest that the interaction zone between the bubbles is twisted and folded.