The 3D Structure and Kinematics of the Local Disk-Halo Interface: Intermediate-velocity Clouds are the Minority of High-altitude Clouds in the Solar Neighborhood
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| Format: | Preprint |
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2026
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| _version_ | 1866913157942870016 |
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| author | O'Neill, Theo J. Saydjari, Andrew K. Zucker, Catherine Koch, Eric W. Benjamin, Robert A. Frank, Philipp Yoshida, Stephanie |
| author_facet | O'Neill, Theo J. Saydjari, Andrew K. Zucker, Catherine Koch, Eric W. Benjamin, Robert A. Frank, Philipp Yoshida, Stephanie |
| contents | Studies of the Milky Way's disk-halo interface have historically identified inflowing and outflowing gas incompatible with disk rotation on the basis of radial velocity, leading to the well-known categories of intermediate-velocity clouds (IVCs) and high-velocity clouds (HVCs). In this work, we leverage recent progress in 3D dust mapping of the Solar Neighborhood to perform the first 3D spatial search for anomalous-velocity clouds at the local disk-halo interface. We identify 1,695 dust clouds within 1.25 kpc of the Sun (with altitudes ranging between z=-646 pc to z=+928 pc) by applying a topological structure finding method to a parsec-resolution 3D dust map. We then evaluate the morphological similarity between these clouds and HI 21 cm emission to measure cloud kinematics, and construct a sample of 519 clouds with high-confidence distances, 3D morphologies, and radial velocities. Among these are several IVCs (embedded within the well-known Intermediate Velocity Arch complex) now identified in 3D for the first time, enabling direct measurement of their distances, sizes, densities, masses, pressures, and dust-to-gas ratios. We observe a pronounced asymmetry in the vertical distribution of all clouds in the Solar Neighborhood, with $(2.9 \pm 0.2) \times$ more clouds in the Northern Galactic hemisphere than the Southern above altitudes at which IVCs are present ($|z| \geq 480$ pc). IVCs make up only 18% of the total number of clouds located at these high altitudes, with the remainder having low velocities -- highlighting the importance of accounting for low-radial-velocity structures when evaluating the local disk-halo interface and modeling feedback-driven Galactic fountain flows. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2605_24342 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The 3D Structure and Kinematics of the Local Disk-Halo Interface: Intermediate-velocity Clouds are the Minority of High-altitude Clouds in the Solar Neighborhood O'Neill, Theo J. Saydjari, Andrew K. Zucker, Catherine Koch, Eric W. Benjamin, Robert A. Frank, Philipp Yoshida, Stephanie Astrophysics of Galaxies Studies of the Milky Way's disk-halo interface have historically identified inflowing and outflowing gas incompatible with disk rotation on the basis of radial velocity, leading to the well-known categories of intermediate-velocity clouds (IVCs) and high-velocity clouds (HVCs). In this work, we leverage recent progress in 3D dust mapping of the Solar Neighborhood to perform the first 3D spatial search for anomalous-velocity clouds at the local disk-halo interface. We identify 1,695 dust clouds within 1.25 kpc of the Sun (with altitudes ranging between z=-646 pc to z=+928 pc) by applying a topological structure finding method to a parsec-resolution 3D dust map. We then evaluate the morphological similarity between these clouds and HI 21 cm emission to measure cloud kinematics, and construct a sample of 519 clouds with high-confidence distances, 3D morphologies, and radial velocities. Among these are several IVCs (embedded within the well-known Intermediate Velocity Arch complex) now identified in 3D for the first time, enabling direct measurement of their distances, sizes, densities, masses, pressures, and dust-to-gas ratios. We observe a pronounced asymmetry in the vertical distribution of all clouds in the Solar Neighborhood, with $(2.9 \pm 0.2) \times$ more clouds in the Northern Galactic hemisphere than the Southern above altitudes at which IVCs are present ($|z| \geq 480$ pc). IVCs make up only 18% of the total number of clouds located at these high altitudes, with the remainder having low velocities -- highlighting the importance of accounting for low-radial-velocity structures when evaluating the local disk-halo interface and modeling feedback-driven Galactic fountain flows. |
| title | The 3D Structure and Kinematics of the Local Disk-Halo Interface: Intermediate-velocity Clouds are the Minority of High-altitude Clouds in the Solar Neighborhood |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2605.24342 |