4 Conclusion

Whatever the direction of the line of sight a diffuse local component is widely observed from Galactic longitude 301$^\circ$ to 323$^\circ$. Linked to the local arm, this component is associated with the Coalsack and other dark clouds in the vicinity, and also to the OB Sco-Cen association which is at the origin of this negative interstellar medium velocity component ($-10 < V_{\rm lsr} < 0$ km $\rm s^{-1}$) between l = 295$^\circ$ and 341$^\circ$  (Crawford 1991). We thus choose a distance of 170 pc for this component.

Except for this diffuse component and the distant sources with positive velocities, the H$\alpha$ emission produced by discrete and diffuse sources shows a rather intricate kinematic behaviour. Indeed, the velocity components exhibit a large range of variation difficult to interpret in terms of independent groups, particularly toward areas where the regions are likely exhibiting large internal motions, e.g. at l = 305$^\circ$. In some zones (e.g. at l = 320$^\circ$) a study with wider observing fields would be necessary to conclude.

We have tried to distinguish the different complexes met along the various lines of sight using the multiwavelength information. Some groups have velocities allowing no kinematic distance determination due to circular rotation departures.

In order to interpret the studied area in terms of the spiral structure we need to connect it with the adjacent zones observed in the H$\alpha$ Survey. This study is in progress.

Acknowledgements

The authors are most grateful to J. Caplan for English translation.