H I jet G40-15 from a rotating cloud in the 4-kpc molecular ring: Magnetized outflow and formation of a dense star cluster

摘要

A giant H I spur centered on (l, b) = (40degrees, - 15degrees), (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 120 km s(-1) with the center velocity at similar to 100 km s(-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 similar to 3 x 10(5) M-circle dot, and the energy to lift the mass from the galactic plane is similar to 10(52) 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.