Observational evidence for rotational desorption of Complex Molecules by radiative torques from Orion BN/KL

TL;DR

This study provides observational evidence that radiative torques can cause rotational desorption of complex organic molecules in star-forming regions, explaining their presence at lower temperatures than previously thought.

Contribution

It demonstrates the role of radiative torque-induced rotational desorption in releasing COMs at low temperatures, supported by ALMA observations and polarization data analysis.

Findings

COMs detected at temperatures below 100 K.

Polarization degree decreases with increasing dust temperature.

Observational support for rotational desorption mechanism.

Abstract

Complex Organic Molecules (COMs) are believed to form in the ice mantle of dust grains and are released to the gas by thermal sublimation when grain mantles are heated to temperatures of $T_{\rm d}\gtrsim 100\,\rm K$. However, some COMs are detected in regions with temperatures below 100 K. Recently, a new mechanism of rotational desorption due to centrifugal stress induced by radiative torques (RATs) is proposed by Hoang & Tram 2020 that can desorb COMs at low temperatures. In this paper, we report observational evidence for rotational desorption of COMs toward the nearest massive star-forming region Orion BN/KL. We compare the abundance of three representative COMs which have very high binding energy computed by the rotational desorption mechanism with observations by ALMA, and demonstrate that the rotational desorption mechanism can explain the existence of such COMs. We also analyze the polarization data from SOFIA/HAWC+ and JCMT/SCUBA-2 and find that the polarization degree at far-infrared/submm decreases with increasing the grain temperature for $T_{\rm d}\gtrsim 71\,\rm K$. This is consistent with the theoretical prediction using the Radiative Torque (RAT) alignment theory and Radiative Torque Disruption (RATD) mechanism. Such an anti-correlation between dust polarization and dust temperature supports the rotational disruption as well as rotational desorption mechanism of COMs induced by RATs.