Observational Evidence for Rotational Desorption of Complex Molecules by Radiative Torques from Orion BN/KL

Abstract

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 d ≳ 100 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) was 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 that 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/submillimeter decreases with increasing the grain temperature for T d ≳ 71 K . This is consistent with the theoretical prediction using the RAT alignment theory and Radiative Torque Disruption mechanism. Such an anticorrelation between dust polarization and dust temperature supports the rotational disruption as well as rotational desorption mechanism of COMs induced by RATs.