HIGH-VELOCITY H-I IN THE SPIRAL GALAXY NGC-5668

The nature and origin of the high-velocity clouds (HVCs) of neutral hy drogen in our Galaxy are not well understood, in part because of the u ncertain distances to the clouds. As a result it is difficult to measu re the mass of neutral hydrogen in the HVCs in the Galaxy, but further insight into the nature of HVCs can be obtained by finding and studyi ng such gas in other galaxies. The Sc-galaxy NGC 5668 was found to hav e high-velocity wings beyond the double-horned 21 cm profile in observ ations performed with the Arecibo 305 m telescope; these wings are the expected signature of HVCs in a disk galaxy, In this paper, Very Larg e Array observations of NGC 5668 are presented that confirm the high-v elocity H I wings detected with the Arecibo telescope, About 60% of th e material in the high-velocity wings is distinct in position-velocity diagrams, located primarily outside the optical disk of the galaxy, a nd may be infalling material comparable to the Magellanic Stream in ou r own Galaxy, The total mass of this kinematically distinct neutral hy drogen is 4 x 10(8) M.. A natural source for the rest of the wing mate rial is halo gas produced by a galactic fountain. Such a fountain woul d be driven by supernovae and energetic stellar winds from massive sta rs in OB associations that would also transfer kinetic energy to the n eutral hydrogen disk. This would result in a larger H I velocity dispe rsion within the optical disk than outside of it, as is suggested by t hese observations. (C) 1996 American Astronomical Society.