H I Jet G40—15 from a Rotating Cloud in the 4-kpc Molecular Ring: Magnetized Outflow and Formation of a Dense Star Cluster

A giant H I spur centered on (l, b) = (40◦,−15◦), (G40−15) emanates from G30−00 toward negative high latitude. The spur is known as the Smith cloud and as a high-velocity cloud HVC 40−15+100, while we call it H I jet G40−15. The radial velocity ranges from 80 to 120kms−1 with the center velocity at ∼ 100kms−1. Both the kinematical and positional coordinates are coincident with those of the tangential point of the 4-kpc molecular ring of the Galaxy. We interpret this spur as being a magnetized H I jet emanating from the 4-kpc molecular ring of the galactic disk. The kinematical distance is estimated to be 6.9 kpc from the Sun, and the jet’s top (G50−26) is −3.4kpc high from the galactic plane. The whole extent is 4.4 kpc in length and 300 pc in width. The total H I mass is ∼ 3× 105M , and the energy to lift the mass from the galactic plane is ∼ 1052 erg. We propose an acceleration mechanism of such an extremely high-altitude coherent H I structure by a twisting magnetic jet associated with a collapsing molecular cloud in the galactic disk. We suggest a scenario for the formation of a dense star cluster, such as a globular cluster, from a collapsing cloud core with a twisting magnetic outflow.