The ALMA Survey of 70 $\mu \mathrm{m}$ Dark High-mass Clumps in Early Stages (ASHES). VII: Chemistry of Embedded Dense Cores

Abstract

We present a study of chemistry toward 294 dense cores in 12 molecular clumps using the data obtained from the ALMA Survey of 70 $\mu \mathrm{m}$ dark High-mass clumps in Early Stages (ASHES). We identified 97 protostellar cores and 197 prestellar core candidates based on the detection of outflows and molecular transitions of high upper energy levels ($E_u/k>45$ K). The detection rate of the N${}_2$D${}^{+}$ emission toward the protostellar cores is 38%, which is higher than 9% for the prestellar cores, indicating that N${}_2$D${}^{+}$ does not exclusively trace prestellar cores. The detection rates of the DCO${}^{+}$ emission are 35% for the prestellar cores and 49% for the protostellar cores, which are higher than those of N${}_2$D${}^{+}$, implying that DCO${}^{+}$ appears more frequently than N${}_2$D${}^{+}$ in both prestellar and protostellar cores. Both N${}_2$D${}^{+}$ and DCO${}^{+}$ abundances appear to decrease from the prestellar to protostellar stage. The DCN, C${}_2$D and ${}^{13}$CS emission lines are rarely seen in the dense cores of early evolutionary phases. The detection rate of the H${}_2$CO emission toward dense cores is 52%, three times higher than that of CH${}_3$OH (17%). In addition, the H${}_2$CO detection rate, abundance, line intensities, and line widths increase with the core evolutionary status, suggesting that the H${}_2$CO line emission is sensitive to protostellar activity.

Accepted for Publication in ApJ. 36 pages, 15 figures, 5 tables. Table 5 available at https://github.com/ShanghuoLi/70-um-dark-high-mass-clumps

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