Cloud and Star Formation in Spiral Arms

TL;DR

This paper uses simulations to study giant molecular cloud formation in spiral galaxies, highlighting the roles of cloud collisions, gravitational instabilities, and stellar feedback, and examining how spiral arms influence star formation.

Contribution

It provides new insights into the dominant cloud formation mechanisms at different densities and the impact of stellar feedback on cloud properties, challenging previous assumptions about spiral arms triggering star formation.

Findings

Cloud formation by collisions dominates at low surface densities.

Stellar feedback limits cloud mass and affects cloud properties.

Spiral arms gather gas but do not directly trigger star formation.

Abstract

We present the results from simulations of GMC formation in spiral galaxies. First we discuss cloud formation by cloud-cloud collisions, and gravitational instabilities, arguing that the former is prevalent at lower galactic surface densities and the latter at higher. Cloud masses are also limited by stellar feedback, which can be effective before clouds reach their maximum mass. We show other properties of clouds in simulations with different levels of feedback. With a moderate level of feedback, properties such as cloud rotations and virial parameters agree with observations. Without feedback, an unrealistic population of overly bound clouds develops. Spiral arms are not found to trigger star formation, they merely gather gas into more massive GMCs. We discuss in more detail interactions of clouds in the ISM, and argue that these are more complex than early ideas of cloud-cloud collisions. Finally we show ongoing work to determine whether the Milky Way is a flocculent or grand design spiral.