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Oxford University Press, Publications of Astronomical Society of Japan, Supplement_1(73), p. S117-S128, 2018

DOI: 10.1093/pasj/psy120

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An intermediate-velocity H i cloud falling to the galactic disk; Possible evidence for low-metallicity H i gas originating outside the galactic disk

This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Abstract

Abstract We found that an intermediate-velocity cloud (IVC), IVC 86−36, in H i 21 cm emission shows a head–tail distribution toward the Galactic plane with marked parallel filamentary streamers, which is extended over 40° in the sky. The distance of IVC 86−36 is constrained to be less than ∼3 kpc from absorption of a background star as determined from optical spectroscopy. There is a bridge feature in velocity between the IVC and the local interstellar medium with velocity separation of ∼50 km s−1, which may indicate dynamical interaction of the IVC with the disk. If the interaction is correct, the distance estimate d of the IVC ranges from 200 pc to 3 kpc, and the mass of the IVC head is estimated to be $7\times 10^3(d/1\:\mbox{kpc})^2\, M_{⊙ }$. The IVC shares similar properties to the Smith Cloud located at 12 kpc, including the head–tail distribution, streamers, and bridge feature, while the mass of the IVC is less than ∼0.1 of the Smith Cloud. A comparison between the H i and the Planck/IRAS dust emission indicates that the dust emission of IVC 86−36 is not detectable in spite of its H i column density of 2 × 1020 cm−2, indicating a low metallicity for IVC 86−36, reduced by a factor of $\lesssim \!\!0.2$ as compared with the solar neighbor. We conclude that IVC 86−38 is an infalling cloud which likely originated in the low-metallicity environment of the Galactic halo or the Magellanic system.