Effects of Magnetic Fields on Gas Dynamics and Star Formation in Nuclear Rings

Abstract

Nuclear rings at the centers of barred galaxies are known to be strongly magnetized. To explore the effects of magnetic fields on star formation in these rings and nuclear gas flows, we run magnetohydrodynamic simulations in which there is a temporally constant magnetized inflow to the ring, representing a bar-driven inflow. The mass inflow rate is 1 M _⊙ yr ^−1 , and we explore models with a range of field strength in the inflow. We adopt the TIGRESS framework developed by Kim & Ostriker to handle radiative heating and cooling, star formation, and resulting supernova (SN) feedback. We find that magnetic fields are efficiently amplified in the ring due to rotational shear and SN feedback. Within a few 100 Myr, the turbulent component B _trb in the ring saturates at ∼35 μ G (in rough equipartition with the turbulent kinetic energy density), while the regular component B _reg exceeds 50 μ G. Expanding superbubbles created by clustered SN explosions vertically drag predominantly toroidal fields from near the midplane to produce poloidal fields in high-altitude regions. The growth of magnetic fields greatly suppresses star formation at late times. Simultaneously, strong magnetic tension in the ring drives radially inward accretion flows from the ring to form a circumnuclear disk in the central region; this feature is absent in the unmagnetized model.

Keywords

• Star formation
• Galaxy circumnuclear disk
• Barred spiral galaxies
• Stellar feedback
• Interstellar medium
• Magnetohydrodynamics