Abundant Methanol Ice toward a Massive Young Stellar Object in the Central Molecular Zone

Previous radio observations revealed widespread gas-phase methanol (CH₃OH) in the Central Molecular Zone (CMZ) at the Galactic center (GC), but its origin remains unclear. Here, we report the discovery of CH₃OH ice toward a star in the CMZ, based on a Subaru 3.4-4.0 μm spectrum, aided by NASA/IRTF imaging and 2-4 μm spectra. The star lies ∼8000 au away in projection from a massive young stellar object (MYSO). Its observed high CH₃OH ice abundance (17% ± 3% relative to H₂O ice) suggests that the 3.535 μm CH₃OH ice absorption likely arises in the MYSO's extended envelope. However, it is also possible that CH₃OH ice forms with a higher abundance in dense clouds within the CMZ, compared to within the disk. Either way, our result implies that gas-phase CH₃OH in the CMZ can be largely produced by desorption from icy grains. The high solid CH₃OH abundance confirms the prominent 15.4 μm shoulder absorption observed toward GC MYSOs arises from CO₂ ice mixed with CH₃OH.