Distribution of star-forming complexes and the structure of our Galaxy

Abstract

The determination of the external galaxies morphology is generally based on their appearance on optical images. At these wavelengths young stellar population and their associated H ii regions, which can be grouped into star-forming complexes, appear preferentially located along spiral arms. Hence, it is naturally to use the same tracers to delineate the arms of our own Galaxy. But, where for external galaxies the distribution of star-forming complexes along the spiral arms is generally evident from direct imaging, for our Galaxy the spiral arms are strung out along the line of sight, leading to the superposition and mixing of information from the different complexes in the spiral arms making it difficult to distinguish them. Thus to access to the spatial distribution of young objects, hence to the large scale structure of our Galaxy, it is required first to identify and collect star-forming complexes (molecular clouds – H ii regions – OB stars) and then to determine their distance. In this framework I review the observational results and difficulties concerning the distribution of star-forming complexes and the determination of the structure of our Galaxy.