2026-07-16 九州大学
フィラメント状分子雲に埋め込まれたL1544前恒星コア
＜関連情報＞
- https://www.kyushu-u.ac.jp/ja/researches/view/1521
- https://www.aanda.org/articles/aa/full_html/2026/07/aa58871-26/aa58871-26.html
L1544原始星核へのイオン・中性粒子のドリフト速度の調査 N2 D+および para-NH 2 Dを用いた両極性拡散の検出 Probing the ion-neutral drift velocity toward the L1544 prestellar core Detection of ambipolar diffusion using N2D+ and para-NH2D
Doris Arzoumanian, Silvia Spezzano, Tommaso Grassi, Paola Caselli, Yusuke Tsukamoto, Haruka Fukihara, Yoshiaki Misugi, Felipe Alves, Jaime Pineda, Sigurd Jensen, Elena Redaelli and Alexei Ivlev
Astronomy & Astrophysics Published:10 July 2026
DOI:https://doi.org/10.1051/0004-6361/202658871
Abstract
Context. The dynamical role of the magnetic field in the star formation process is tightly linked to the coupling between matter and the field. This coupling is due to the interaction between ions and neutrals in the partially ionized interstellar medium. When the ionization degree drops in the dense environment of prestellar cores, the magnetic field and matter may decouple, leading to differences in the infalling velocities of ions and neutrals known as ambipolar diffusion.
Aims. The onset of gravitational collapse resulting from ion-neutral decoupling has never been observed. The aim of this work is to search for signatures of ambipolar diffusion within a prestellar core.
Methods. We observed the deuterated N2D+ ion and the neutral para-NH2D species toward the prototypical prestellar core L1544. These two species are ideal tracers of prestellar cores, sampling the same high densities in the core interior. We compared the velocity centroid and linewidth maps of the ion-neutral pair.
Results. We find a mean ion-neutral velocity difference of ∼0.05 km/s toward the core. We interpret the observed ion-neutral velocity difference in L1544 as a signature of ambipolar diffusion by comparing it with predictions from self-consistent calculations of ambipolar resistivity, including dust grain growth. We do not detect a significant ion-neutral linewidth difference that may be attributed to the subsonic infall motions of the gas in L1544 and geometrical effects in the presence of inclination.
Conclusions. These results emphasize the role of dust grain growth at the prestellar core stage in setting the ambipolar resistivity and regulating the dynamical evolution of dense cores toward their collapse into protostars. We propose that measurements of ion-neutral drift velocities provide new constraints on the total magnetic field strength and the dust size distribution within prestellar cores.
