Probing fragmentation with ALMA continuum and spectral line observations of the dense clumps in the l=224° region

We report observations, performed with the Atacama Large Millimeter/submillimeter Array (ALMA), of 1 mm dust continuum emission and molecular line emission in (CO)-C-13(2-1) and (CO)-O-18(2-1), towards a sample of starless and protostellar clumps selected from a region, towards the l = 224 degrees field, of the Herschel Infrared GALactic Plane Survey (Hi-GAL). Using the ALMA images and a source extraction algorithm we have analysed the small-scale (similar to 1000 AU) structure of the clumps and their population of cores (or fragments). We find in general multiple cores in each Hi-GAL clump, both in the continuum and spectral lines, but we do not find a dominant fragmentation mode and the morphologies arc very different among the various sources. Our results suggest that during the transition phase from clump to core, those sources with a higher core formation efficiency are also associated with parent clumps that are more likely to convert a higher fraction of their initial mass into a single or a few cores. We were able to obtain a core mass function, or CoMF, covering masses in the range similar to 2 x 10(-3) to similar to 1 M-circle dot for the (CO)-O-18 cores, and similar to 4 x 10(-2) to similar to 10 M-circle dot for the continuum cores. We find that the CoMF in our sample is much shallower than the higher mass (greater than or similar to 1 M-circle dot) IMF, thus indicating that while approaching the final phase of fragmentation the mass function does not resemble the IMF more closely.