Inflow of neutral gas toward the galactic disk [chapter]

I. F. Mirabel
Structure and Dynamics of the Interstellar medium  
I highlight the evidence for inflow of neutral gas toward the disk of the Galaxy. The Milky Way is accreting 0.2-0.5 M /yr of o extragalactic atomic hydrogen at very high velocities. The interaction of infalling clouds with galactic material produces large-scale disturbances in the interstellar medium. Although the injection of energy into the galactic disk by infalling neutral gas is only 1% of the energy from supernovae, the impinging of high velocity neutral gas may be a relatively important
more » ... source of energy in localized regions of the outer Galaxy. In the solar neighborhood the downfall rate of HI at intermediate -8 -1 -2 -1 velocities is 2.72 x 10 z(kpc) M pc yr , which if representative © of the whole galactic disk, is at least 10 times more massive than the estimated accretion rate of extragalactic HI at very high velocities. This implies that most of the neutral gas that is infalling in the solar vicinity has originated in the galactic disk. It is concluded that in the Milky Way galaxy there is a moderate inflow of extragalactic neutral gas on top of a more intensive disk-halo circulation.
doi:10.1007/bfb0114909 fatcat:hpstmfi4ovgp7n3phqqnyf5pfa