Interstellar Dust as a Regulator of Star Formation: From Ionization Balance to Magnetic Decoupling Across Different Galaxy Types

Interstellar dust plays a fundamental role in regulating the physical and chemical evolution of the interstellar medium (ISM) and star-forming regions across different galaxy types. This study presents a physical framework describing how dust grains influence star formation through a coupled sequence of radiative, chemical, and magnetohydrodynamic processes.

Dust grains efficiently absorb ultraviolet and optical radiation and re-emit the energy in the infrared, modifying the thermal balance of the surrounding gas. Dust surfaces also facilitate recombination by capturing free electrons and ions, decreasing the ionization fraction of the medium. This reduction in ionization weakens the coupling between neutral gas and magnetic fields, enhancing ambipolar diffusion and reducing magnetic support against gravitational collapse.

The associated decrease in gas temperature lowers the Jeans mass, enabling instability at smaller mass scales, while the mass-to-magnetic-flux ratio approaches or exceeds the critical threshold marking the transition to gravitationally dominated collapse.

Comparative analysis of infrared emission from three galaxies of different morphological type—the spiral galaxy NGC 628, the elliptical galaxy NGC 1399, and the irregular galaxy NGC 1427A—supports this sequence, showing that dust-rich systems display structured emission consistent with active star formation, whereas the dust-poor elliptical galaxy shows diffuse emission consistent with suppressed star formation.

This framework demonstrates that interstellar dust acts as an active regulator of star formation rather than a passive component of the interstellar medium.