Protostars at Subsolar Metallicity: First Detection of Large Solid-state Complex Organic Molecules in the Large Magellanic Cloud

The Astrophysical Journal Letters, vol. 992, pp. L30

Abstract

Abstract We present the results of James Webb Space Telescope observations of the protostar ST6 in the Large Magellanic Cloud (LMC) with the Medium Resolution Spectrograph of the Mid-Infrared Instrument (4.9–27.9 μ m). Characterized by one-third to half-solar metallicity and strong UV radiation fields, the environment of the LMC allows us to study the physics and chemistry of star-forming regions under conditions similar to those at earlier cosmological epochs. We detected five icy complex organic molecules (COMs): methanol (CH 3 OH), acetaldehyde (CH 3 CHO), ethanol (CH 3 CH 2 OH), methyl formate (HCOOCH 3 ), and acetic acid (CH 3 COOH). This is the first conclusive detection of CH 3 COOH ice in an astrophysical context, and CH 3 CHO, CH 3 CH 2 OH, and HCOOCH 3 ices are the first secure detections outside the Galaxy and in a low-metallicity environment. We address the presence of glycolaldehyde (HOCH 2 CHO, a precursor of biomolecules), an isomer of HCOOCH 3 and CH 3 COOH, but its detection is inconclusive. ST6’s spectrum is also rich in simple ices: H 2 O, CO 2 , CH 4 , SO 2 , H 2 CO, HCOOH, OCN − , HCOO − , NH 3 , and NH 4 + . We obtain the composition and molecular abundances in the icy dust mantles by fitting the spectrum in the 6.8–8.4 μ m range with a large sample of laboratory ice spectra using the ENIIGMA fitting tool or the local continuum method. We found differences in the simple and COM ice abundances with respect to H 2 O ice between ST6 and Galactic protostars that likely reflect differences in metallicity and UV flux. More laboratory ice spectra of COMs are needed to better reconstruct the observed infrared spectra of protostars.

Authors 14

1. M. Sewiło corresponding

   Goddard Space Flight Center · University of Maryland, College Park

   Affiliation as printed

   Center for Research and Exploration in Space Science and Technology, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

   Department of Astronomy, University of Maryland, College Park, MD 20742, USA

2. W. R. M. Rocha corresponding Aachen Laboratory for Astrophysics, Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, NL 2300 RA Leiden, The Netherlands

3. M. L. van Gelder corresponding Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL 2300 RA Leiden, The Netherlands

4. M. G. Navarro corresponding

   Astronomical Observatory of Rome · National Institute for Astrophysics

   Affiliation as printed

   INAF—Osservatorio Astronomico di Roma, Via di Frascati 33, 00078 Monte Porzio Catone, Italy

5. Steven B. Charnley corresponding

   Goddard Space Flight Center

   Affiliation as printed

   Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

6. M. Jin corresponding

   Goddard Space Flight Center · Catholic University of America

   Affiliation as printed

   Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

   Department of Physics, Catholic University of America, Washington, DC 20064, USA

7. Joana M. Oliveira corresponding

   Keele University

   Affiliation as printed

   Lennard-Jones Laboratories, Keele University, ST5 5BG, UK

8. Jacco Th. van Loon corresponding

   Keele University

   Affiliation as printed

   Lennard-Jones Laboratories, Keele University, ST5 5BG, UK

9. Logan Francis corresponding Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL 2300 RA Leiden, The Netherlands

10. Jennifer J. Wiseman corresponding

    Goddard Space Flight Center

    Affiliation as printed

    Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

11. R. Indebetouw corresponding

    National Radio Astronomy Observatory · University of Virginia

    Affiliation as printed

    Department of Astronomy, University of Virginia, PO Box 400325, Charlottesville, VA 22904, USA

    National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903, USA

12. C.‐H. Rosie Chen corresponding

    Max Planck Institute for Radio Astronomy

    Affiliation as printed

    Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

13. Roya Hamedani Golshan corresponding

    University of Cologne

    Affiliation as printed

    I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937, Köln, Germany

14. D. Qasim corresponding

    Southwest Research Institute

    Affiliation as printed

    Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78238, USA