From cold cores to hot cores in massive IRDCs: An SMA follow-up survey of IRDC cores observed with Herschel.
Howard Smith (CfA), Qizhou Zhang (CfA), Jonathan Foster (BU), Susanna Finn (BU), Patrick Jonsson (CfA), James Jackson (BU), Sergio Molinari (INAF-IFSI), Serena Viti (UCL), Maite Beltran (INAF-Osservatorio di Arcetri) and Ricardo Cesaroni (INAF-Osservatori
Infrared dark clouds (IRDCs) represent the earliest stages in massive star and star cluster formation. Despite the large efforts to establish their global properties, little is known about their internal physical and chemical structure, and evolution. We present the first interferometric (~0.5"−5") survey of the chemical composition of 8 IRDC clumps carried out with the SMA. The cores are classified as Cold (CC), Warm (WC) and Hot (HC), depending on their dust temperature, source complexity, and chemical composition. CC (T~20 K) are not bright in dust continuum and are chemically inactive. WC (T~45 K) are bright but do not show internal structure, with molecular line emission from only H2CO, CH3CN or CH3OH. HC (T>100 K) are bright, complex and chemically very rich. By comparing our SMA results with gas-grain chemical models, we find that the differences in the core chemistry are explained by the selective desorption of molecules from grain mantles, as the temperature increases with core evolution.