The ALMA-QUARKS survey: – I. Survey description and data reduction

In the Turbulent Core model, massive prestellar cores are suggested as the precursors of massive stars. However, only a handful of these candidates have been discovered so far. We conducted highresolution ALMA observations at Band 3 (∼ 2′′, 6000 au) and Band 6 (∼ 0.3′′, 900 au) targeting the MM1 clump in the filamentary infrared dark cloud (IRDC) G34.43+0.24. Our observations reveal cores MM1-C and E1 as prestellar core candidates with masses of 71 and 20 M⊙ and radii of 2100–4400 au, and they show no obvious sign of active star-formation activities. In particular, MM1-C is a promising massive prestellar core candidate. Within MM1-C, we detected two extremely dense substructures, C1 and C2, as characterized by nH2 ∼ 108−9cm−3. Moreover, evidence of further fragmentation in C2 was also found. We have detected the primordial fragmentation in the earliest stage of massive star formation. We speculate that MM1-C would be the birthplace of a massive multiple system.