Investigating the role of magnetic fields in star formation using molecular line profiles

Determining the importance of magnetic fields in star-forming environments is hampered by the difficulty of accurately measuring both field strength and gas properties in molecular clouds. We post-process three-dimensional non-ideal magnetohydrodynamic simulations of pre-stellar cores with a time-dependent chemical network, and use radiative transfer modelling to calculate self-consistent molecular line profiles. Varying the initial mass-to-flux ratio from subcritical to supercritical results in significant changes to both the intensity and shape of several observationally important molecular lines. We identify the peak intensity ratio of N 2 H ⁺ to CS lines, and the CS J = 2–1 blue-to-red peak intensity ratio, as promising diagnostics of the initial mass-to-flux ratio, with N 2 H ⁺ /CS values of >0.6 (<0.2) and CS blue/red values of <3 (>5) indicating subcritical (supercritical) collapse. These criteria suggest that, despite presently being magnetically supercritical, L1498 formed from subcritical initial conditions.