The Discovery of 25 μm Interstellar Methanol

We present the first astrophysical detection of methanol (CH3OH) in the torsional band near 25 μm. Using high resolution mid-infrared (MIR) spectroscopy, we identified over seventy gas-phase CH3OH absorption lines between 20 and 28 μm towards the massive protostar NGC 7538 IRS 1 with SOFIA/EXES. We derive a temperature of 180 K and a total column density of 2 × 1017 cm−2, comparable to sub-mm surveys. These MIR absorption lines likely probe the CH3OH in the disk close to the central star, as confirmed by complementary analysis of C2H2. Furthermore, we report the detection of the same 25 μm CH3OH absorption feature in JWST/MIRI archival data towards a massive protostar, five Class 0 and Class I low mass protostars, and eleven protoplanetary disks. The detection of this CH3OH feature through three stages of protostellar evolution suggests that this molecule has been directly inherited from the icy, natal cloud phase. The access to this CH3OH band will enable further exploration of how complex organic molecules could be inherited from the earliest protostellar disks and survive to the central regions of planet forming disks, where future planets will reside. Indeed, this work has nearly tripled the total number of protoplanetary disks with CH3OH detections. We provide an updated line list for the torsional band of CH3OH, which was generated from lab work and computation.