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From Massive Protostars to a Giant HII Region: Submillimeter Imaging of the Galactic Mini-starburst W43

We have carried out a submillimeter continuum and spectroscopic study of the W43 main complex, a massive star-forming region, which harbors a giant HII region. The maps reveal a filamentary structure containing ~50 fragments with masses 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 ~ 10^6 cm^-3) suggest that they are protoclusters and excellent sites to form massive stars. Follow-up observations are necessary, but we have already identified three protoclusters to be very good candidates for containing very young massive protostars. The starburst cluster, that excites the giant HII region has a large impact on the molecular complex. However, it remains unclear if this first episode of star formation is triggering the formation of new massive stars, through ionization shocks crossing the closeby molecular clouds. W43 is thus an ideal laboratory to investigate massive star formation from the protostellar phase to that of giant HII regions. Moreover, the very active star-forming complex W43 may be considered a Galactic mini-starburst region that could be used as a miniature model of starburst galaxies.