| Ever since their discovery, submillimetre galaxies (SMGs) have been regarded as some of the most fascinating, but also controversial objects in the early Universe. Their potentially fundamental role in cosmic evolution - as prominent contributors to the global stellar mass growth - has been widely debated while a number of important aspects of their nature remained speculative. The lack of high-resolution imaging of large samples of SMGs at their discovery wavelength made multi-wavelength associations difficult, generally unreliable and often even impossible, with unpredictable consequences to the inferred number statistics and redshift distribution of this galaxy population. Already in Cycle 0 ALMA's capabilities paved the way for a detailed 870um (band 7) continuum view of the flux-limited sample of 126 SMGs in the Extended Chandra Deep Field South. I will discuss how only 10 hours of ALMA integration time boost our understanding of SMGs with respect to their source number counts and counterpart association but also to (serendipitously) reveal starbursts and insights into cooling processes in the interstellar medium in the very early Universe. During this talk, I will also briefly refer to ongoing and upcoming efforts in ALMA's Cycle 1 to investigate the SMG population, particularly its most distant constituents at redshifts of z>4.
This image shows a selection of the galaxies as seen in the sharp new observations by ALMA (in red). The ALMA observations, at submillimetre wavelengths, are overlaid on an infrared view of the region as seen by the IRAC camera on the Spitzer Space Telescope (coloured blue).