Chemical variation in molecular cloud cores in the Orion A Cloud. III

Abstract

Abstract We carried out mapping observations of N2H+, CCS, cyclic C3H2, H13CO+, HCO+, and HCN lines toward six cores in the Orion A cloud with the Nobeyama 45 m telescope and the KVN (Korean VLBI Network) 21 m telescope. The N2H+ and CCS data were observed with the Nobeyama 45 m and the other lines were observed with the KVN 21 m telescope. We examined the chemical characteristics of the cores and found a tendency for the column density ratio, N(c-C3H2)/N(CCS), to be low in starless regions while it is high in star-forming regions. We also found that N(H13CO+) is enhanced in cluster-forming regions compared with those in isolated star-forming regions. Furthermore, we found that the N(NH3)/N(CCS) and N(NH3)/N(HC3N) ratios are high in star-forming cores and low in starless cores in the Orion A cloud for a wide range of kinetic temperature, Tk = 10 to 60 K. We suggest that the N(NH3)/N(CCS), N(NH3)/N(HC3N), and N(N2H+)/N(CCS) ratios may be indicators of chemical evolution in giant molecular clouds, including warmer regions. From a comparison between cores associated with protostars and cores without protostars through virial analysis, we also suggest that the dissipation of turbulence initiates star formation. Finally, we found that the N(NH3)/N(CCS) ratio increases with the dissipation of turbulence. This may suggest that the chemical evolution can be an indicator of the dynamical evolution of the core.