Now Reading: The Discovery Of 25 um Interstellar Methanol
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The Discovery Of 25 um Interstellar Methanol
25.3 µm map of the NGC 7538 region from SOFIA/Faint Object infraRed Camera (FORCAST; Herter et al. 2013) archival data (Cycle 1 Program 0034, PI A. G. G. M. Tielens). Our target and brightest source, IRS 1, is at the centre with offset 0′′, 0′′ corresponding to α(J2000) = 23:13:45.37, δ(J2000) = +61:28:10.5. The positions of IRS 1 and the dimmer sources (IRS 2, IRS 3, IRS 1E, and IRS 1SE) are given by Sandell et al. (2020). In solid green is the 8.7′′×3.2′′ EXES slit from this work’s 23.9 µm setting (Table A1), and in dashed blue the 14′′ and 18′′ JCMT beams (van der Tak et al. 2000; Bisschop et al. 2007) whose CH3OH results we will use for a comparison (Section 5.1). au scale uses a distance of 2.65 kpc (Moscadelli et al. 2009). Note the logarithmic scale for the flux, which exaggerates the brightness of the non-IRS 1 sources. — astro-ph.GA
We present the first astrophysical detection of methanol (CH3OH) in the torsional band near 25 um.
Using high resolution mid-infrared (MIR) spectroscopy, we identified over seventy gas-phase CH3OH absorption lines between 20 and 28 um 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 x 10^17 cm-2, comparable to sub-mm measurements. Complementary analysis of acetylene (C2H2) absorption lines is also included.
Both CH3OH and C2H2 reveal an unresolved second velocity component. These MIR absorption lines likely probe the molecular material in two edge-on disks, supporting the scenario that NGC 7538 IRS 1 consists of multiple protostars.
We provide an updated line list for the torsional band of CH3OH, which was generated from lab work and model calculations. This discovery and the updated line list will enable the search for CH3OH in JWST/MIRI spectra.
Sarah L. Nickerson, Naseem Rangwala, Keeyoon Sung, Xinchuan Huang, Edward J. Montiel, Curtis DeWitt, Valentin J. M. Le Gouellec, Sean W. J. Colgan, Jason Dittmann, Jose Pablo Fonfría, Graham M. Harper, Kathleen E. Kraemer, Jialu Li, Conor A. Nixon, Maisie Frances Rashman, Clara Sousa-Silva, Alexander G. G. M. Tielens, William D. Vacca
Comments: Accepted for publication in The Astrophysical Journal Letters (ApJL); 21 pages, 6 Figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2508.00059 [astro-ph.GA] (or arXiv:2508.00059v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2508.00059
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Submission history
From: Sarah Nickerson
[v1] Thu, 31 Jul 2025 18:00:02 UTC (362 KB)
https://arxiv.org/abs/2508.00059
Astrobiology, astrochemistry,
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