A pan-galaxy study of synthetic giant molecular filaments: a turbulence-dominated life cycle

Abstract

Recent surveys of the Galactic plane have revealed dozens of giant molecular filaments (GMFs), with lengths ranging from tens to hundreds of parsecs, yet their origins and life cycles remain debated. In this work, we analyze over 700 GMFs identified from synthetic CO emission maps of a high-resolution magnetohydrodynamic simulation of a Milky Way-like galaxy, whose lengths range from $\sim 10$ pc to $\sim 300$ pc. We find that turbulent shock from galactic shear and stellar feedback are the primary drivers of GMF formation. Magnetized turbulence dominates their internal dynamics, supporting the filaments against global collapse while simultaneously inducing fragmentation into dense clumps. This fragmentation follows the turbulence-driven sausage instability model, rather than pure Jeans instability, and triggers efficient star formation along the filaments. Cloud-cloud collisions are frequent, affecting more than $70\%$ of GMFs, and often disrupt or reshape their morphology. The typical filamentary lifetime is $t_{\text{fil}} \sim 14$ Myr, comparable to the crossing time of giant molecular clouds (GMCs). The molecular gas half-life is $\sim 7$ Myr, similar to that of GMCs, indicating that GMFs are transient but dynamically important structures.

Figures (16)

• Figure 1: Milky Way–like spiral galaxy simulation at $t = 720$ Myr. Upper left: total gas column density map, where $N_\mathrm{H}$ is the total column density of H nuclei. Upper right: molecular hydrogen column density traced by synthetic CO $J = 1 \rightarrow 0$ emission. The cyan contours illustrate the positions of GMFs identified in \ref{['sec:GMF_identify']}. Each map covers $30 \times 30$ kpc with a pixel size of 1 pc. Lower left: mass weighted B field strength map. The green arrows indicate the local magnetic field directions in the x-y plane. Lower right: the mass-weighted mean magnetic field as a function of time in the second stage of this simulation.
• Figure 2: Left panel: Face-on $N_\mathrm{H_2, CO}$ column density map of a $(600~\rm pc)^2$ region in the simulated galaxy. The spines of identified face-on GMFs are shown as red lines. Right panel: Edge-on view of the selected GMF in the grey box in the left panel. Note that the connected filament in the edge-on view consists of two components in the face-on view.
• Figure 3: Box-and-whisker plots showing the distributions of GMF length (top left), width (top right), mass (bottom left), and linear mass (bottom right). Solid lines indicate the median, while dashed lines indicate the mean. Colors and labels in the center identify the data source of each GMF sample.
• Figure 4: Histogram of the ratio between the synthetic GMF linear mass $\mu$ and the virial linear mass $\mu_\mathrm{vir}$. The vertical grey dashed line indicates $\mu/\mu_\mathrm{vir} = 1$.
• Figure 5: Top panel: Ratio between the molecular mass from 3D contours surrounding the CoM of GMF $M_\mathrm{3D}$ and the molecular mass from 2D synthetic observations $M_\mathrm{2D}$. The x-axis shows the value of the number density threshold of different 3D contours. The blue dotted line shows the median value of the ratios from the synthetic edge-on GMF catalog; while the grey band illustrates the 25th to 75th range of the ratios. Bottom panel: ratio between the molecular hydrogen mass above a given $n_\mathrm{H_2,CO}$ threshold and the total molecular hydrogen mass.