Chemical Variation in Molecular Cloud Cores in the Orion A Cloud

TL;DR

This study investigates the chemical composition of molecular cloud cores in Orion A GMC, revealing the first detection of CCS and its distribution, and analyzing chemical evolution indicators influenced by star formation activity and temperature.

Contribution

First detection of CCS in Orion A GMC and analysis of its distribution and chemical evolution indicators in relation to star formation activity.

Findings

CCS detected in about one-third of cores, widely distributed.

CCS and HC3N intensities are higher in the southern region.

Star formation near Orion KL enhances HC3N emission.

Abstract

We have observed molecular cloud cores in the Orion A giant molecular cloud (GMC) in CCS, HC3N, DNC, and HN13C to study their chemical characteristics. We have detected CCS in the Orion A GMC for the first time. CCS was detected in about a third of the observed cores. The cores detected in CCS are not localized but are widely distributed over the Orion A GMC. The CCS peak intensity of the core tends to be high in the southern region of the Orion A GMC. The HC3N peak intensity of the core also tends to be high in the southern region, while there are HC3N intense cores near Orion KL, which is not seen in CCS. The core associated with Orion KL shows broad HC3N line profile, and star formation activity near Orion KL seems to enhance the HC3N emission. The column density ratio of NH3 to CCS is lower near the middle of the filament, and is higher toward the northern and southern regions along the Orion A GMC filament. This ratio is known to trace the chemical evolution in nearby dark cloud cores, but seems to be affected by core gas temperature in the Orion A GMC: cores with low NH3 to CCS column density ratios tend to have warmer gas temperature. The value of the column density ratio of DNC to HN13C is generally similar to that in dark cloud cores, but becomes lower around Orion KL due to higher gas temperature.