The life cycle of giant molecular clouds in simulated Milky Way-mass galaxies

¹ Institute for Advanced Study, Tsinghua University, Beijing 100084, People’s Republic of China
² Department of Astronomy, Tsinghua University, Beijing 100084, People’s Republic of China
³ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴ Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
⁵ Department of Physics and Astronomy “Augusto Righi”, University of Bologna, Via P. Gobetti 93/2, I-40129 Bologna, Italy
⁶ INAF, Astrophysics and Space Science Observatory Bologna, Via P. Gobetti 93/3, I-40129 Bologna, Italy
⁷ Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA

^⋆ Corresponding author: hliastro@tsinghua.edu.cn

Received: 13 February 2025
Accepted: 31 May 2025

Abstract

Context. Giant molecular clouds (GMCs) are the primary sites of star formation in galaxies. Their evolution, driven by the interplay of gravitational collapse, stellar feedback, and galactic dynamics, is key to understanding local star formation on GMC scales. However, tracking the full life cycle of GMCs across diverse galactic environments remains challenging and requires high-resolution hydrodynamical simulations and robust post-processing analysis.

Aims. We aim to trace the complete life cycle of individual GMCs in high-resolution Milky Way–mass galaxy simulations to determine how different stellar feedback mechanisms and galactic-scale processes govern cloud lifetimes, mass evolution, and local star formation efficiency (SFE).

Methods. We identified GMCs in simulated galaxies and tracked their evolution using cloud evolution trees. Via cloud evolution trees, we quantified the lifetimes and SFE of GMCs. We further applied our diagnostics to a suite of simulations with varying star formation and stellar feedback subgrid models and explored their impact together with galactic environments to the GMC life cycles.

Results. Our analysis reveals that GMCs undergo dynamic evolution, characterized by continuous gas accretion, gravitational collapse, and star formation, followed by disruption due to stellar feedback. The accretion process sustains the gas content throughout most of the GMC life cycles, resulting in a positive correlation between GMC lifetimes and their maximum masses. The GMC lifetimes range from a few to several tens of million years, with two distinct dynamical modes: (1) GMCs near the galactic center experience strong tidal disturbances, prolonging their lifetimes when they remain marginally unbound; (2) those in the outer regions are less affected by tides, remain gravitationally bound, and evolve more rapidly. In all model variations, we observe that GMC-scale SFE correlates with the baryonic surface density of GMCs, consistent with previous studies of isolated GMCs. Additionally, we emphasize the critical role of galactic shear in regulating GMC-scale star formation and refine the correlation between local SFE and surface density by including its effects. These findings demonstrate how stellar feedback and galactic-scale dynamics jointly shape GMC-scale star formation in realistic galactic environments.