Early-stage star forming cloud cores in GLIMPSE Extended Green Objects (EGOs) as traced by organic species

TL;DR

This study investigates the chemical composition and physical properties of early-stage massive star forming cores in EGOs by analyzing organic molecules, revealing similarities to hot cores and hot corinos but challenging existing chemical models.

Contribution

It provides detailed measurements of organic species in EGO cloud cores and compares their properties with other star-forming regions, highlighting discrepancies with current chemical models.

Findings

EGO cloud cores have methanol temperatures around 44 K.

Abundances of organic species are correlated across different cloud types.

Chemical models do not fully explain observed abundance ratios.

Abstract

In order to investigate the physical and chemical properties of massive star forming cores in early stages, we analyse the excitation and abundance of four organic species, CH3OH, CH3OCH3, HCOOCH3 and CH3CH2CN, toward 29 Extended Green Object (EGO) cloud cores that were observed by our previous single dish spectral line survey. The EGO cloud cores are found to have similar methanol J_3-J_2 rotation temperatures of ~44 K, a typical linear size of ~0.036 pc, and a typical beam averaged methanol abundance of several 10^(-9) (the beam corrected value could reach several 10^(-7)). The abundances of the latter three species, normalized by that of methanol, are found to be correlated also across a large variety of clouds such as EGO cloud cores, hot corinos, massive hot cores and Galactic Center clouds. The chemical properties of the EGO cloud cores lie between that of hot cores and hot corinos. However, the abundances and abundance ratios of the four species can not be satisfactorily explained by recent chemical models either among the EGO cloud cores or among the various types of cloud cores from literature.