4 Conclusions

1.

We have mapped the strong star-forming complex N 11 in the J = 1-0 $~{\rm ^{12}CO}$ line. Additional data were obtained in the J = 2-1 $~{\rm ^{12}CO}$ line, and in the corresponding transitions of $~{\rm ^{13}CO}$.

2.

A total of 29 individual clouds could be identified. As the N 11 area was not completely mapped and not fully sampled, the actual number of clouds is probably higher. The clouds are distributed in a ring or shell surrounding the OB association LH 9, and in a ridge extending to the northeast which appears to be associated with the supergiant shell SGS 1.

3.

With an 11 pc linear resolution, most of the clouds are barely resolved. With a two times higher resolution, most of the emission is seen to come from again barely resolved structures in these clouds. If the virial theorem is taken for guidance, the individual clouds have masses ranging from 0.5 to 7.5 $\times 10^{4}~M_{\odot}$, with a mean of $2.5 \times 10^{4}~M_{\odot}$.

4.

Unlike the apparently quiescent northeastern ridge, the ring region appears to be an extreme photon-dominated region (PDR). The high overall CO to $~{\rm H_{2}}$ conversion factor Xof this PDR greatly contrasts with the almost "normal'' conversion factors of individual dense CO clouds which more effectively resist the strong UV radiation from the embedded OB associations LH 9, LH 10 and LH 13.

5.

There is very little diffuse CO emission between the clouds, and indeed in the N 11 complex as a whole. Nevertheless, diffuse $~{\rm H_{2}}$ not sampled by CO because of the PDR nature of the complex should be be present in significant amounts. This is particularly true for the ring region.

Acknowledgements

It is a pleasure to thank the operating personnel of the SEST for their support, and Alberto Bolatto for valuable assistance in the reduction stage. M.R. wishes to acknowledge support from FONDECYT through grants Nos. 1990881 and 7990042.