A molecular line study towards massive extended green object clumps in the southern sky: chemical properties

TL;DR

This study investigates the chemical properties of massive star-forming regions in the southern sky using molecular line data, revealing how certain molecules serve as indicators of star formation stages.

Contribution

It provides new insights into the chemical evolution of massive star-forming clumps and proposes molecular abundance ratios as chemical clocks for star formation stages.

Findings

N2H+ and C2H emissions originate from quiescent gas.

Abundance ratios decrease from MYSOs to HII regions.

N2H+ and C2H depletion indicates late-stage star formation.

Abstract

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 HII regions. Our results seem to support that N2H+ and C2H emissions mainly come from the gas inside quiescent clumps. In addition, we also find that the [N2H+]/[H13CO+] and [C2H]/[H13CO+] relative abundance ratios decrease from MYSOs to HII regions. These results suggest depletion of N2H+ and C2H in the late stages of massive-star formation, probably caused by the formation of HII regions inside. N2H+ and C2H might be used as chemical clocks for massive-star formation by comparing with other molecules such as H13CO+ and HC3N.