From Massive Protostars to a Giant HiiRegion: Submillimeter Imaging of the Galactic Ministarburst W43

We have carried out a submillimeter continuum and spectroscopic study of theW43 main complex, a massive star-forming region, which harbors a giant HIIregion. The maps reveal a filamentary structure containing ~50 fragments withmasses of 40-4000 Msun and typical diameters of 0.25 pc. Their large sizes,large non-thermal velocities (Dv ~ 5 km/s), and high densities (n_H2 ~ 10^6cm^-3) suggest that they are protoclusters and excellent sites to form massivestars. Follow-up observations are necessary, but we have already identifiedthree protoclusters to be very good candidates for containing very youngmassive protostars. The starburst cluster, that excites the giant HII regionhas a large impact on the molecular complex. However, it remains unclear ifthis first episode of star formation is triggering the formation of new massivestars, through ionization shocks crossing the closeby molecular clouds. W43 isthus an ideal laboratory to investigate massive star formation from theprotostellar phase to that of giant HII regions. Moreover, the very activestar-forming complex W43 may be considered a Galactic mini-starburst regionthat could be used as a miniature model of starburst galaxies.Comment: 20 pages, 13 figures, to be published in Astrophysical Journa