The Superclouds of the Local Milky Way

Abstract: Recent 3D dust maps of the local Milky Way are revolutionizing our understanding of the Sun's Galactic neighborhood, bringing much-needed insight into the large-scale organization of the interstellar medium. Focusing on the largest scales in $\textit{Gaia}$-based 3D dust maps, we find a pattern of seven highly elongated, mostly parallel structures in the local $5\,\mathrm{kpc}^2$, five of which were previously unknown. These structures show pitch angles of $33.5 \pm 4.0 ^\circ$, and masses ranging from $10^5$ to $10^6$ $M_\odot$. We refer to these structures as superclouds. Nearly all known star-forming regions in the solar neighborhood lie within the superclouds, primarily along their central axes, supporting the idea that they are precursors to giant molecular clouds. All but one of the seven superclouds show an underlying undulation, indicating that this is not a property unique to the Radcliffe wave. We find that while the superclouds have line masses that vary by about a factor of four, their volume densities vary by about 10$\%$ only. This suggests that superclouds self-regulate their physical sizes and internal structure to maintain pressure equilibrium with their environment. These findings establish a new framework for understanding how large-scale Galactic structures shape the conditions for star formation in the solar vicinity, and likely in galaxies like the Milky Way.