Investigation of Chemical Differentiation among the NGC2264 Cluster-Forming Clumps

Abstract

We have carried out mapping observations of molecular emission lines of HC${}_3$N and CH${}_3$OH toward two massive cluster-forming clumps, NGC2264-C and NGC2264-D, using the Nobeyama 45-m radio telescope. We derive an $I$(HC${}_3$N)/$I$(CH${}_3$OH) integrated intensity ratio map, showing a higher value at clumps including 2MASS point sources at the northern part of NGC2264-D. Possible interpretations of the $I$(HC${}_3$N)/$I$(CH${}_3$OH) ratio are discussed. We have also observed molecular emission lines from CCS and N${}_2$H${}^{+}$ toward five positions in each clump. We investigate the $N$(N${}_2$H${}^{+}$)/$N$(CCS) and $N$(N${}_2$H${}^{+}$)/$N$(HC${}_3$N) column density ratios among the ten positions in order to test whether they can be used as chemical evolutionary indicators in these clumps. The $N$(N${}_2$H${}^{+}$)/$N$(CCS) ratio shows a very high value toward a bright embedded IR source (IRS1), whereas the $N$(N${}_2$H${}^{+}$)/$N$(HC${}_3$N) ratio at IRS1 is comparable with those at the other positions. These results suggest that UV radiation affects the chemistry around IRS1. We find that there are positive correlations between these column density ratios and the excitation temperatures of N${}_2$H${}^{+}$, which implies the chemical evolution of clumps. These chemical evolutionary indicators likely reflect the combination of evolution along the filamentary structure and evolution of each clump.

5 figures, 9 tables, and 3 figures in appendix, 19 pages, Accepted by the Monthly Notices of the Royal Astronomical Society

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