Herschel observations of the W43 mini-starburst

Aims. To explore the infrared and radio properties of one of the closest Galactic starburst regions. Methods. Images obtained with the Herschel Space Observatory at wavelengths of 70, 160, 250, 350, and 500 mu m using the PACS and SPIRE arrays are analyzed and compared with radio continuum VLA data and 8 mu m images from the Spitzer Space Observatory. The morphology of the far-infrared emission is combined with radial velocity measurements of millimeter and centimeter wavelength transitions to identify features likely to be associated with the W43 complex. Results. The W43 star-forming complex is resolved into a dense cluster of protostars, infrared dark clouds, and ridges of warm dust heated by massive stars. The 4 brightest compact sources with L > 1.5 x 10(4) L-circle dot embedded within the Z-shaped ridge of bright dust emission in W43 remain single at 4 '' (0.1 pc) resolution These objects, likely to be massive protostars or compact clusters in early stages of evolution are embedded in clumps with masses of 103 to 104 M-circle dot, but contribute only 2% to the 3.6x10(6) L-circle dot far-IR luminosity of W43 measured in a 16 by 16 pc box. The total mass of gas derived from the far-IR dust emission inside this region is similar to 10(6) M-circle dot. Cometary dust clouds, compact 6 cm radio sources, and warm dust mark the locations of older populations of massive stars. Energy release has created a cavity blowing-out below the Galactic plane. Compression of molecular gas in the plane by the older H II region near G30.684-0.260 and the bipolar structure of the resulting younger W43 H II region may have triggered the current mini-star burst.