Interplay between Stellar Spirals and the ISM in Galactic Disks

TL;DR

This paper presents a new dynamical model of galactic spirals based on high-resolution simulations, showing that gas and stellar spirals are formed by different mechanisms and are non-steady, influencing star formation.

Contribution

It introduces a novel simulation-based framework for understanding the interplay between stellar and gas spirals in galactic disks, emphasizing their non-steady nature and distinct formation processes.

Findings

Gas spirals form through different mechanisms than stellar density waves.

Stellar arms are non-steady, wound, and stretched by galactic shear.

Star clusters form from dense gas within ~30 Myrs, aligned with stellar arms.

Abstract

We propose a new dynamical picture of galactic stellar and gas spirals, based on hydrodynamic simulations in a `live' stellar disk. We focus especially on spiral structures excited in a isolated galactic disk without a stellar bar. Using high-resolution, 3-dimensional N-body/SPH simulations, we found that the spiral features of the gas in galactic disks are formed by essentially different mechanisms from the galactic shock in stellar density waves. The stellar spiral arms and the interstellar matter on average corotate in a galactic potential at any radii. Unlike the stream motions in the galactic shock, the interstellar matter flows into the local potential minima with irregular motions. The flows converge to form dense gas clouds/filaments near the bottom of the stellar spirals, whose global structures resemble dust-lanes seen in late-type spiral galaxies. The stellar arms are non-steady; they are wound and stretched by the galactic shear, and thus local densities of the arm change on a time scale of ~ 100 Myrs, due to bifurcating or merging with other arms. This makes the gas spirals associated with the stellar arms non-steady. The association of dense gas clouds are eventually dissolved into inter-arm regions with non-cirucular motions. Star clusters are formed from the cold, dense gases, whose ages are less than ~30 Myrs, and they are roughly associated with the background stellar arms without a clear spatial offset between gas spiral arms and distribution of young stars.