Abstract
Abstract Three-dimensional (3D) magnetic field information on molecular clouds and cores is important for revealing their kinematical stability (magnetic support) against gravity, which is fundamental for studying the initial conditions of star formation. In the present study, the 3D magnetic field structure of the dense starless core FeSt 1-457 is determined based on the near-infrared polarimetric observations of the dichroic polarization of background stars and simple 3D modeling. With an obtained angle of line-of-sight magnetic inclination axis of and previously determined plane-of-sky magnetic field strength of 23.8 ± 12.1 , the total magnetic field strength for FeSt 1-457 is derived to be 33.7 ± 18.0 . The critical mass of FeSt 1-457, evaluated using both magnetic and thermal/turbulent support is , which is identical to the observed core mass, . We thus conclude that the stability of FeSt 1-457 is in a condition close to the critical state. Without infalling gas motion and no associated young stars, the core is regarded to be in the earliest stage of star formation, i.e., the stage just before the onset of dynamical collapse following the attainment of a supercritical condition. These properties could make FeSt 1-457 one of the best starless cores for future studies of the initial conditions of star formation.
Highlights
Three-dimensional (3D) information on astronomical objects is essential for discussing their morphology, diversity, origin, and evolution, as well as for determining their physical parameters
For dense molecular clouds and their cores, it is important to know the inclination angle of the magnetic field direction toward the line of sight to investigate their magnetic support against self-gravity through the measurements of the mass-to-magnetic flux ratio, compared with the critical value suggested by theory
The value of the mass-to-magnetic flux ratio determines the stability of the core, and if the total magnetic field strength can be accurately determined using 3D magnetic field information, i.e., line-of-sight field inclination angle, the stability as well as evolutionary status of the core can be discussed
Summary
Three-dimensional (3D) information on astronomical objects is essential for discussing their morphology, diversity, origin, and evolution, as well as for determining their physical parameters. For dense molecular clouds and their cores, it is important to know the inclination angle of the magnetic field direction (magnetic axis) toward the line of sight to investigate their magnetic support against self-gravity through the measurements of the mass-to-magnetic flux ratio, compared with the critical value suggested by theory The line-of-sight inclination angle of the magnetic field has not been extensively measured, and the ratios of the observational mass-to-flux ratios to the theoretical critical value, l = (M F)obs (M F)critical , have been determined mostly based on statistical considerations 1333 IRAS 4A (Girart et al 2006) was compared with theoretical models of the collapse of the magnetized cloud (Gonçalves et al 2008), resulting in a determination of the 3D magnetic structure around the protostar as well as the line-ofsight magnetic inclination angle qinc of 0°–30° or 25°–55°. The model maps obtained at each inclination angle can be compared with the observations
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