Letter to the Editor

Modeling the magnetic field in the protostellar source NGC 1333 IRAS 4A

¹ Centro de Astronomia e Astrofísica da Universidade de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal e-mail: goncalve@oal.ul.pt
² INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy e-mail: galli@arcetri.astro.it
³ Institut de Ciències de l'Espai (CSIC–IEEC), Campus UAB–Facultat de Ciències, Torre C5–Parell 2, 08193 Bellaterra, Catalunya, Spain e-mail: girart@ieec.cat

Received: 26 August 2008
Accepted: 25 September 2008

Abstract

Context. Magnetic fields are believed to play a crucial role in the process of star formation.

Aims. We compare high-angular resolution observations of the submillimeter polarized emission of NGC 1333 IRAS 4A, tracing the magnetic field around a low-mass protostar, with models of the collapse of magnetized molecular cloud cores.

Methods. Assuming a uniform dust alignment efficiency, we computed the Stokes parameters and synthetic polarization maps from the model density and magnetic field distribution by integrations along the line-of-sight and convolution with the interferometric response.

Results. The synthetic maps are in good agreement with the data. The best-fitting models were obtained for a protostellar mass of 0.8 , of age 9  10⁴ yr, formed in a cloud with an initial mass-to-flux ratio ~2 times the critical value.

Conclusions. The magnetic field morphology in NGC 1333 IRAS 4A is consistent with the standard theoretical scenario for the formation of solar-type stars, where well-ordered, large-scale, rather than turbulent, magnetic fields control the evolution and collapse of the molecular cloud cores from which stars form.