We study the core mass function (CMF) within 32 dense clumps in seven infrared dark clouds (IRDCs) with the Atacama Large Millimeter/submillimeter Array via 1.3mm continuum emission at a resolution of ~1". We have identified 107 cores with the dendrogram algorithm, with a median radius of about 0.02pc. Their masses range from 0.261 to 178M_{sun}. After applying completeness corrections, we fit the combined IRDC CMF with a power law of the form dN/d.logM{propto}M^-{alpha}^ and derive an index of {alpha}~0.86+/-0.11 for M>=0.79M{sun} and {alpha}~0.70+/-0.13 for M>=1.26M{sun}, which is a significantly more top-heavy distribution than the Salpeter stellar initial mass function index of 1.35. We also make a direct comparison of these IRDC clump CMF results to those measured in the more evolved protocluster G286 derived with similar methods, which have {alpha}~1.29+/-0.19 and 1.08+/-0.27 in these mass ranges, respectively. These results provide a hint that, especially for the M>=1.26M{sun}_ range where completeness corrections are modest, the CMF in high pressure, early-stage environments of IRDC clumps may be top-heavy compared to that in the more evolved, global environment of the G286 protoclusters. However, larger samples of cores probing these different environments are needed to better establish the robustness of this potential CMF variation.

Cone search capability for table J/ApJ/862/105/table1 (Estimated physical parameters for 1.3mm continuum cores)