Letter to the Editor

FAUST

XV. A disc wind mapped by CH₃OH and SiO in the inner 300 au of the NGC 1333 IRAS 4A2 protostar

¹ ESO, Karl Schwarzchild Srt. 2, 85478 Garching bei München, Germany
e-mail: marta.desimone@eso.org
² INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
³ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁴ National Radio Astronomy Observatory, 1003 Lopezville Rd, Socorro, NM 87801, USA
⁵ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin-d’Hères, France
⁶ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, A.P. 3-72 (Xangari), 8701 Morelia, Mexico
⁷ Instituto de Astronomía, Universidad Nacional Autónoma de México, Ciudad Universitaria, A.P. 70-264, Cuidad de México 04510, Mexico
⁸ The Institute of Physical and Chemical Research (RIKEN), 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan
⁹ NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
¹⁰ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 5C2, Canada
¹¹ Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹² Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
¹³ IRAP, Université de Toulouse, CNRS, CNES, UPS, Toulouse, France
¹⁴ Excellence Cluster ORIGINS, Boltzmannstraße 2, 85748 Garching bei Muünchen, Germany
¹⁵ Center for Astrochemical Studies, Max-Planck-Institut für extraterrestrische Physik (MPE), Gießenbachstr. 1, 85741 Garching, Germany
¹⁶ Centre for Frontier Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
¹⁷ Department of Chemistry, University of Virginia, McCormick Road, PO Box 400319 Charlottesville, VA 22904, USA
¹⁸ The University of Texas at Austin, 2515 Speedway, Austin, TS 78712, USA
¹⁹ The Graduate University for Advanced Studies (SOKENDAI), Shonan Village, Hayama, Kanagawa 240-0193, Japan

Received: 12 March 2024
Accepted: 29 April 2024

Abstract

Context. Understanding the connection between outflows, winds, accretion, and discs in the inner protostellar regions is crucial for comprehending star and planet formation processes.

Aims. We aim to we explore the inner 300 au of the protostar IRAS 4A2 as part of the ALMA FAUST Large Program.

Methods. We analysed the kinematical structures of SiO and CH₃OH emission with 50 au resolution.

Results. The emission arises from three zones: (i) a very compact and unresolved region (< 50 au) dominated by the ice sublimation zone, at ±1.5 km s⁻¹ with respect to v_sys, traced by methanol; (ii) an intermediate region (between 50 au and 150 au) traced by both SiO and CH₃OH, between 2 and 6 km s⁻¹ with respect to v_sys, with an inverted velocity gradient (with respect to the large-scale emission), whose origin is not clear; (iii) an extended region (> 150 au) traced by SiO, above 7 km s⁻¹ with respect to v_sys, and dominated by the outflow. In the intermediate region, we estimated a CH₃OH/SiO abundance ratio of about 120–400 and a SiO/H₂ abundance of 10⁻⁸. We explored various possibilities to explain the origin of this region, such as, a rotating disc or inner envelope, a jet on the plane of the sky or precessing, and a wide-angle disc wind.

Conclusions. We propose that CH₃OH and SiO in the inner 100 au probe the base of a wide-angle disc wind. The material accelerated in the wind crosses the plane of the sky, giving rise to the observed inverted velocity gradient, and sputtering the grain mantles and cores releasing CH₃OH and SiO. This is the first detection of a disc-wind candidate in SiO, and the second ever in CH₃OH.