Live Fast, Die Young: GMC lifetimes in the FIRE cosmological simulations of Milky Way-mass galaxies

TL;DR

This study measures the lifetimes of Giant Molecular Clouds in cosmological simulations of Milky Way-like galaxies, revealing typical lifetimes of 5-7 million years and environmental influences on their evolution.

Contribution

First measurement of GMC lifetimes in cosmological simulations at high resolution, linking cloud properties with galactic environment and star formation.

Findings

GMCs have lifetimes of 5-7 Myr, mostly under 20 Myr.

GMC lifetime decreases with higher virial parameter.

GMC lifetime weakly increases with galactocentric radius.

Abstract

We present the first measurement of the lifetimes of Giant Molecular Clouds (GMCs) in cosmological simulations at $z = 0$, using the Latte suite of FIRE-2 simulations of Milky Way-mass galaxies. We track GMCs with total gas mass $\gtrsim 10^5$ M$_\odot$ at high spatial ($\sim1$ pc), mass ($7100$ M$_{\odot}$), and temporal (1 Myr) resolution. Our simulated GMCs are consistent with the distribution of masses for massive GMCs in the Milky Way and nearby galaxies. We find GMC lifetimes of $5-7$ Myr, or 1-2 freefall times, on average, with less than 2$\%$ of clouds living longer than 20 Myr. We find decreasing GMC lifetimes with increasing virial parameter, and weakly increasing GMC lifetimes with galactocentric radius, implying that environment affects the evolutionary cycle of GMCs. However, our GMC lifetimes show no systematic dependence on GMC mass or amount of star formation. These results are broadly consistent with inferences from the literature and provide an initial investigation into ultimately understanding the physical processes that govern GMC lifetimes in a cosmological setting.