From Massive Protostars to a Giant H II Region: Submillimeter Imaging of the Galactic Ministarburst 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 H II region. The maps reveal a filamentary structure containing ~50 fragments with masses of 40-4000 M_solar and typical diameters of 0.25 pc. Their large sizes, large nonthermal velocities (Δv~5 km s^-1), and high densities (n_H2~10⁶ 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 H II region has a large impact on the molecular complex. However, it remains unclear whether 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 H II regions. Moreover, the very active star-forming complex W43 may be considered a Galactic ministarburst region that could be used as a miniature model of starburst galaxies.