IISER MOHALI

Abstract: The alignment of spinning, non-spherical dust grains with Galactic magnetic fields (B-fields) in the interstellar medium (ISM) provides a unique window into the role of B-fields in star formation. As unpolarized stellar light or dust continuum emission traverses through aligned dust grains, it becomes partially and linearly polarized. This polarization fraction reveals properties of the dust grains, while the polarization angle traces the plane-of-the-sky component of the B-field. Consequently, optical, near-infrared, and sub-millimeter polarimetry have emerged as powerful tools for mapping B-field geometries, from low-density, large-scale diffuse ISM to high-density, small-scale cores. Observations reveal that B-fields play a crucial role in channeling gas flows to form elongated, filamentary molecular clouds. The energy budget of B-fields is often comparable to that of turbulence, with both counteracting gravity to regulate star formation. This interplay contributes to the low observed star formation efficiency and the prolonged lifespan of molecular clouds. However, the relative importance of B-fields, turbulence, and gravity remains poorly understood due to the challenges of constraining B-field morphology and strength compared to the other two agents. To fully understand the role of B-fields, it is critical to analyze the energy budgets of these three agents and their spatial distributions across scales and densities in molecular clouds. While the geometry and influence of B-fields are well understood in the diffuse ISM and low-density portions of the molecular clouds, their role in dense clumps and cores remains elusive. In this seminar, I will present key findings from sensitive sub-millimeter dust polarization observations of two contrasting regions: the low-mass dense cores in Taurus B213 and the high-mass dense clump in Cepheus A—progenitors of Sun-like stars and massive protostellar clusters, respectively. In B213, the energies of magnetic fields (EB), turbulence (ET), and gravity (EG) are comparable, indicating equipartition. However, core-scale gas kinematics reshape the local B-fields, decoupling them from the dynamically important, uniform fields of the parent cloud. In contrast, Cepheus A exhibits a hierarchical energy distribution (EG > EB > ET), where gravity dominates the other two forces. As the primary player, gravity drags B-fields and drives gas flows toward the gravitational potential well. As a secondary player, B-field regulates the flow direction, smoothing gas motion and mitigating instabilities and fragmentation. This interplay results in gravity-driven, magnetically regulated accretion flows that fuel the formation of protostellar clusters at high accretion rates. I will also highlight results from other collaborative projects and outline future research plans related to the role of magnetic fields in star formation processes.