Protostellar Outflows at the EarliesT Stages (POETS)

IX. Magnetohydrodynamic disk winds traced by SO and SO₂ in luminous protostars

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius (CA), Italy
⁴ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁵ Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
⁶ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
⁷ Universidad Nacional Autónoma de México, Instituto de Radioastronomía y Astrofísica, Antigua Carretera a Pátzcuaro 8701, Ex-Hda. San José de la Huerta, 58089 Morelia, Michoacán, Mexico
⁸ Department of Physics and Astronomy, McMaster University, 1280 Main St. W, Hamilton, ON L8S 4K1, Canada
⁹ Institut de Ciències de l’Espai (ICE), CSIC, Campus UAB, Carrer de Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain
¹⁰ Institut d’Estudis Espacials de Catalunya (IEEC), 08860 Castelldefels, Barcelona, Spain
¹¹ Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
¹² Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, CT2 7NH, UK
¹³ Universidad Autónoma de Chile, Nucleo Astroquimica y Astrofisica, Avda Pedro de Valdivia 425, Providencia, Santiago de Chile, Chile

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 25 March 2026
Accepted: 30 May 2026

Abstract

Context. Magnetohydrodynamic (MHD) disk winds (DWs) can be responsible for removing angular momentum from the accretion disks of protostars, for driving mass accretion and disk evolution and dispersal, and, ultimately, for setting the conditions for planet formation.

Aims. We want to investigate two massive young stellar objects (YSOs), IRAS 21078+5211 and G035.02+0.35, where evidence for MHD DWs has been previously obtained at scales of 10–100 au through measurements of the 22 GHz water maser velocity distribution within the Protostellar Outflows at the EarliesT Stages survey. The different mass, 5.6±2 M_⊙ and ≈20 M_⊙, of the two YSOs allows us to investigate the dependence of MHD DWs on the YSO environment, too.

Methods. We employed IRAM Northern Extended Millimeter Array and archival Atacama Large Millimeter Array observations of IRAS 21078+5211 and G035.02+0.35, respectively, to study the gas kinematics and physical conditions of the corresponding protostellar winds on scales of 100–1000 au using the same molecular tracers.

Results. In IRAS 21078+5211, the emissions of several molecules, particularly SO, SO₂, CH₃CN, and CH₃OH, are distributed along the axis of the previously identified radio jet, and present a local standard of rest velocity (V_LSR) gradient transversal to the jet axis. Position-velocity (PV) plots of the SO lines show patterns consistent with Keplerian rotation. The SO₂ emission comes from high-velocity gas flowing close to the jet axis, while CH₃CN and CH₃OH present a larger radial extension than the S-bearing species. In G035.02+0.35, the same molecules are instead distributed along the (sky-projected) major axis of the rotating disk reported previously, and their V_LSR gradients consistently trace the disk rotation. The corresponding PV plots present Keplerian profiles. SO is the only molecular species whose emission extends well outside the disk. Our analysis shows that, in both YSOs, the spatial and velocity distributions of SO are consistent with a rotating wind magneto-centrifugally launched from the YSO disk. The comparison with models of molecule formation and excitation in shocks indicates that the different radial extension of the molecular species observed in the protostellar wind of IRAS 21078+5211, as well as the lack of molecules, except SO, in the G035.02+0.35’s wind, can be well explained in terms of a radially extended MHD DW, rather than a compact X-wind.

Conclusions. This study provides compelling evidence that the SO and SO₂ emissions can be used to trace MHD DWs in luminous YSOs at scales of 100–1000 au, and confirms the results derived with water masers at scales of 10–100 au.