2020ApJ...901...31L

To search for the potential chemical dependence on physical conditions, we have carried out the study of chemistry on the nine protostellar clumps of the high-mass star-forming infrared dark cloud G034.43+00.24, with observations of several ∼1 mm lines by the Atacama Pathfinder EXperiment telescope. They include CO/¹³CO/C¹⁸O (2-1), HCO⁺/H¹³CO⁺ (3-2), HCN/H¹³CN (3-2), HNC (3-2), CS/C³⁴S (5-4), SiO (6-5), SO (6-5), p-H₂CO (3-2), and CH₃OH (5-4). All the clumps are simply grouped into two classes: high-luminosity protostellar clumps (MM1-MM4, L_bol> ∼10³L_☉) and low-luminosity protostellar clumps (MM5-MM9, L_bol≪10³L_☉). Our observations indicate that ¹³CO suffers either no or low depletion in the clump environment of G034.43+00.24 as characterized by a nearly constant level of the ¹³CO abundance distribution. For the remaining relatively dense gas tracers, we find that their abundances tend to get enhanced in the high-luminosity protostellar clumps as opposed to the low-luminosity counterparts. We suggest that for most, if not all, of the dense gas tracers the high abundance mainly arises from both the high luminosities and associated outflows of the high-luminosity protostellar clumps while the low abundance could be due to the lack of such active star-forming activities in the low-luminosity protostellar clumps.