TA-Lab Colloquium

(Last update on 7th May 2026)

Next Talk

Date/Room 21 May at 14:00 in ES606
Speaker Izumi Seno (TA-Lab., Nagoya Univ.)
Title Precipitation from the Galactic Halo As a Fuel for Star Formation in the Galactic Disk
Abstract To sustain the Galactic star formation rate over ~10 Gyr, continuous gas accretion from the halo is required. High-Velocity Clouds (HVCs), which is ~10^4 K HI gas condensing from the ~10^6 K hot halo plasma via thermal instability, are considered a key source of this accreting gas. Determining the exact mass accretion rate of these falling HI clouds is crucial for understanding the evolution of the Galaxy. However, an uncertainty of an order of magnitude remains from both observational and theoretical perspectives, partly because previous models overestimated the physical sizes of these clouds. In this presentation, we conduct 2D hydrodynamical simulations to investigate the underlying physics that determines this accretion rate and to quantify the resulting gas accretion. Our simulations, which incorporate the Galactic gravitational potential, radiative cooling, and thermal conduction, reveal that these warm HI clouds form via approximately isochoric cooling followed by compression from the surrounding medium. During this process, the accreting clouds effectively dissipates compressional heating through radiative cooling, maintaining its thermal state and naturally explaining the observed compact sizes. Furthermore, we find a saturated mass accretion rate of ~ 6 solar masses per year onto the Galactic disk. This confirms that halo thermal instability provides a sufficient and steady gas supply to sustain long-term star formation. Finally, we will discuss the steady-state conditions of the Milky Way, a new sound-wave-driven formation scenario for HVC complexes, and connections to future radio and X-ray observations.