Low and high velocity clouds produced by young stellar clusters

Abstract

Intermediate and high velocity HI clouds rain onto the plane of our Galaxy. They are observed at heights of between 500 and 1500 pc, falling onto the Galactic plane at velocities from 50 to 140 km s${}^{-1}$. To explain the origin of these clouds, we present a galactic fountain model, driven by the wind from a super stellar cluster (SSC). We solve the equations for a steady, radiative de Laval nozzle flow. We consider two effects not considered previously in astrophysical nozzle flow models: cooling functions for different metallicities, and the direct action of the galactic gravitational field on the gas flowing along the nozzle. For an adiabatic nozzle flow, the gravity acting directly on the gas within the nozzle "stalls" the nozzle flow for initial wind velocities lower than the escape velocity from the Galaxy. For the same wind velocity, a radiative nozzle flow stalls at lower altitudes above the galactic plane. We find that SSC winds with velocities of $v_w=500-800$ km s${}^{-1}$ produce nozzles stall at heights of $x_m=1-15$ kpc. The stalled nozzle flow then rains back onto the galactic plane at velocities in the range observed in intermediate and high velocity HI clouds. We study a nozzle flow driven by a wind from a SSC close to the Galactic centre. We find that for velocities within the range expected for a SSC wind, we can produce nozzle flows that stall above the galactic plane. These stalled flows produce cool, infalling clouds with velocities similar to those of intermediate and high velocity HI clouds.

7 pages, 6 figures. A&A, in press

References in corpus (5)

• Stellar populations in the nuclei of late-type spiral galaxies
• Hydrodynamical simulations of Galactic fountains II: evolution of multiple fountains
• Two-Dimensional Hydrodynamic Models of Super Star Clusters with a Positive Star Formation Feedback
• Hydrodynamical simulations of Galactic fountains I: evolution of single fountains
• Gemini Spectroscopy and HST Imaging of the Stellar Cluster Population in Region B of M82

Cited by in corpus (5)

• The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays
• Wild at Heart:-The Particle Astrophysics of the Galactic Centre
• Non-Thermal Insights on Mass and Energy Flows Through the Galactic Centre and into the Fermi Bubbles
• Improved Cosmic-Ray Injection Models and the Galactic Center Gamma-Ray Excess
• A ring-shaped starburst as a galactic wind-generating mechanism: Morphology, emission, and mass ejection