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Yamato Matsuzuki

Publications and source records attributed to Yamato Matsuzuki.

2 recordsLinked to original sources
arXiv2026

Mapping of the Cold Neutral Medium via HI Phase Separation in an Atomic Cloud Undergoing Molecular Cloud Formation

We investigate the atomic-to-molecular gas transition in the molecular cloud formation region HLCG 92-35 using GALFA-H I and NANTEN 12CO(J=1-0) observations. The HI spectra were decomposed into Cold Neutral Medium (CNM), Lukewarm Neutral Medium (LNM), and Warm Neutral Medium (WNM) components with the ROHSA algorithm, and CNM structures were identified using Astrodendro. The derived HI mass ratio is CNM:LNM:WNM = 43:47:10, indicating that a substantial fraction of the gas resides in the intermediate-temperature phase. We identify 1792 CNM clumps with characteristic sizes of ~1-2 pc and average densities of ~ 80 cm^{-3}, broadly consistent with theoretical predictions for CNM structures formed through thermal instability. The CNM mass spectrum exhibits a power-law slope similar to that of CO clumps, suggesting that molecular clouds inherit the hierarchical structure established in the atomic phase. Significant non-thermal linewidths and localized CNM-CO velocity offsets imply that the CNM consists of small-scale cloudlets with distinct kinematic properties. These results provide observational support for a scenario in which small-scale CNM structures produced by thermal instability and turbulent flows represent an early stage of molecular cloud formation.

astro-ph.GA↗
arXiv2026

Search for Seeds of The Cradle of Stars: Study of The Evolution From Atomic to Molecular Hydrogen Clouds with 1000 AU Scale Resolution

The aim of this science case for SKA1-Mid is to elucidate the spatial and velocity structure of the Cold Neutral Medium (CNM) on scales below the Field length, thereby elucidating the physical processes that govern CNM structure formation and its role in the earliest stages of molecular cloud formation. This goal will be achieved through a unique observational combination of several-arcsecond angular resolution, high velocity resolution, and unprecedented surface-brightness sensitivity. These observations will reveal the characteristic size, morphology, velocity structure, and internal dynamics of CNM clumps, and will directly connect such structures to the earliest phases of the atomic to molecular transition. Full-polarization observations with SKA1-Mid will also enable emission-based Zeeman measurements of the CNM, allowing the magnetic field strength to be mapped and opening a new window on the role of magnetic fields in CNM formation and evolution. In particular, this will make it possible to determine whether magnetic fields primarily inhibit fragmentation by supporting the gas against compression, or instead guide anisotropic condensation and promote the development of small-scale CNM structure through thermal instability. In combination with interferometric spatial filtering and high spectral resolution, SKA1-Mid will selectively trace the CNM and robustly identify individual clumps in both position and velocity space. These capabilities will provide decisive tests of thermal instability and the two-phase turbulence model, and will establish a new observational foundation for understanding how molecular clouds emerge from the multi-phase atomic interstellar medium.

astro-ph.GA↗