Publication Date:
2015-06-15
Description:
We present a molecular line study towards 31 extended green object (EGO) clumps in the southern sky using data from MALT90 (Millimetre Astronomy Legacy Team 90 GHz). According to previous multiwavelength observations, we divide our sample into two groups: massive young stellar objects (MYSOs) and H ii regions. The most detected lines are N 2 H + ( J = 1 – 0), HCO + ( J = 1 – 0), HNC ( J = 1 – 0), HCN ( J = 1 – 0), HC 3 N ( J = 10 – 9), H 13 CO + ( J = 1 – 0), C 2 H ( N = 1 – 0) and SiO ( J = 2 – 1), indicating that most EGOs are indeed associated with dense clumps and recent outflow activities. The velocity widths of the N 2 H + ( J = 1 – 0), H 13 CO + ( J = 1 – 0), C 2 H ( N = 1 – 0) and HC 3 N ( J = 10 – 9) lines are comparable to each other in MYSOs. However, in H ii regions the velocity widths of the N 2 H + ( J = 1 – 0) and C 2 H ( N = 1 – 0) lines tend to be narrower than those of H 13 CO + ( J = 1 – 0) and HC 3 N ( J = 10 – 9). Our results seem to support that N 2 H + and C 2 H emissions mainly come from the gas inside quiescent clumps. In addition, we also find that the [N 2 H + ]/[H 13 CO + ] and [C 2 H]/[H 13 CO + ] relative abundance ratios decrease from MYSOs to H ii regions. These results suggest depletion of N 2 H + and C 2 H in the late stages of massive-star formation, probably caused by the formation of H ii regions inside. N 2 H + and C 2 H might be used as chemical clocks for massive-star formation by comparing with other molecules such as H 13 CO + and HC 3 N.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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