Superbubbles as the source of dynamical friction: Gas migration, and stellar and dark matter contributions

Abstract

The gas distribution in galaxies is smooth on large scales, but is usually time-dependent and inhomogeneous on smaller scales. The time-dependence originates from processes such as cloud formation, their collisions, and supernovae (SNe) explosions, which also create inhomogeneities. The inhomogeneities in the matter distribution give rise to variations in the local galactic gravitational potential, which can contribute to dynamically coupling the gas disc to the stellar and the dark matter (DM) components of the galaxy. Specifically, multiple SNe occurring in young stellar clusters give rise to superbubbles (SBs), which modify the local acceleration field and alter the energy and momentum of stars or DM particles traversing them, in broad analogy to the dynamical friction caused by a massive object. Our aim is to quantify how the acceleration field from SBs causes dynamical friction and contributes to the secular evolution of galaxies. In order to assess this, we constructed the time-dependent density modifications to the gas distribution that mimics a SB. By evaluating the acceleration field from these density modifications, we were able to see how the momentum or angular momentum of the gas hosting the SBs changes when stars pass through the SB. Combining the effects of all the stars and SBs, we constructed an empirical approximation formula for the momentum loss in homogeneous and isotropic cases. We find that the rate at which the gas disc loses its specific angular momentum via the above process is up to 4% per Gyr, which translates to under one-half of its original value over the lifetime of the disc. For comparison, the mass transfer rate from SBs is about one order of magnitude less than from gas turbulence, and hence the SB contribution should be included to account for the gas migration rate more accurately than 10%. Finally, we studied how the dynamical coupling of the gas disc with the DM halo depends on assumptions on the halo kinematics (e.g. rotation) and found a ∼0.3% variation in the gas disc secular evolution between different DM kinematic models.