Complex Organic Molecules at High Spatial Resolution Toward Orion-KL II: Kinematics

TL;DR

This study uses high-resolution millimeter imaging to analyze how physical conditions influence the distribution of complex organic molecules in Orion-KL, revealing that some molecules are chemically robust while others are sensitive to environmental changes.

Contribution

It provides detailed spatial analysis of molecular distributions in Orion-KL, disentangling chemical processing effects from physical condition influences using high-resolution observations.

Findings

Acetone is chemically robust across varying conditions.

Formic acid is easily destroyed in warm, dense regions.

Physical conditions shape small-scale molecular emission structures.

Abstract

It has recently been suggested that chemical processing can shape the spatial distributions of complex molecules in the Orion-KL region and lead to the nitrogen-oxygen "chemical differentiation" seen in previous observations of this source. Orion-KL is a very dynamic region, and it is therefore also possible that physical conditions can shape the molecular distributions in this source. Only high spatial resolution observations can provide the information needed to disentangle these effects. Here we present millimeter imaging studies of Orion-KL at various beam sizes using the Combined Array for Research in Millimeter-Wave Astronomy (CARMA). We compare molecular images with high spatial resolution images that trace the temperature, continuum column density, and kinematics of the source in order to investigate the effects of physical conditions on molecular distributions. These observations were conducted at \lambda = 3 mm and included transitions of ethyl cyanide [C2H5CN], methyl formate [HCOOCH3], formic acid [HCOOH], acetone [(CH3)2CO], SiO, and methanol [CH3OH]. We find differences in the molecular distributions as a function of each of these factors. These results indicate that acetone may be produced by chemical processing and is robust to large changes in physical conditions, while formic acid is readily destroyed by gas-phase processing in warm and dense regions. We also find that while the spatial distributions of ethyl cyanide and methyl formate are not distinct as is suggested by the concept of "chemical differentiation", local physical conditions shape the small-scale emission structure for these species.