The Role of Magnetic Fields Across Different Scales in the Early Stages of Star Formation

Abstract

We investigate the role of magnetic fields in the early stages of star formation and across a variety of scales. We start by focusing on a nearby molecular cloud Lynds 43 and investigating the magnetic field in relation to the density structure, the outflow of a protostellar object and its role compared to turbulent motions and gravity. We then expand this analysis towards other nearby, low-mass star forming regions. We focus primarily on the magnetic field strength and its orientation to the cores and other density structures, as well as its role compared to turbulent motions and gravity. We then move two orders of magnitude further away to the Central Molecular Zone where we investigate the role of the magnetic field in shaping the large-scale kinematics of the region, specifically how it can help inform an orbital model for the material within the CMZ. We also calculate magnetic field strengths of individual clouds and investigate the overall contribution of the magnetic field and also how it relates to the density structures of the individual clouds.

In L43, we find an evolutionary gradient along the isolated filament that L43 is embedded within, with the most evolved source closest to the Sco OB2 association. One of the protostars drives a CO outflow that has created a cavity in the dust structure to the southeast. We find a magnetic field that appears to be aligned with the cavity walls of the outflow. We also find a magnetic field strength of _160_30 _G in the main starless core and up to _90_40 _G in the more diffuse, extended region. These field strengths give magnetically super- and sub-critical values respectively and both are found to be roughly trans-Alfvenic. When we extend some of this analysis to other nearby low-mass star forming regions, we find that many of the evolved cores are already magnetically super-critical and have field strengths in the range of 30{130 _G. We do not find any preferential alignment of the magnetic fields with either the core orientation or the large-scale magnetic field.

In the CMZ we find that the magnetic field follows a proposed orbital model in the western half, but not as well in the eastern half. The eastern half is significantly more confusing with both gas kinematics and the amount of material there which could be affecting the magnetic _eld we observe. Our proposed orbit is continuous in position-velocity space except for a gap in continuity between roughly Sgr A* and the `Brick,' a known chaotic area where open ends of an orbit may be crossing. We also find that the clouds in the CMZ have large magnetic field strengths, on the order of mG, and a majority are sub-Alfvenic and magnetically sub-critical. This suggests a strong influence of the magnetic field within the molecular clouds of the CMZ.

We finally bring all of the sources together to investigate overall trends based on the magnetic field information. We assume that as clouds start to become gravitationally bound, material can then be dragged across magnetic field lines, hence altering their orientation. We find that there is not a single magnetic field strength versus column density relation that explains differing orientations between small-scale magnetic fields in cores and the large-scale magnetic field around it. In the CMZ, we also find that the magnetic field is preferentially perpendicular to the density structure in a majority of the clouds. Compared to conclusions from nearby star-forming regions, this would suggest that the magnetic field is now at the stage of helping to feed material onto central hubs from which star formation may occur. We also find that different modes of star-formation have distinct magnetic field patterns that are common across a variety of sources.