ar X iv : a st ro - p h / 04 08 13 4 v 1 6 A ug 2 00 4 H i Distribution and Kinematics of UGCA 86

We present 21-cm H i line and 408 MHz and 1.4 GHz continuum observations of the Magellanic dwarf galaxy UGCA 86, made with the DRAO synthesis telescope. UGCA 86 is detected in the continuum at both frequencies, with 408 MHz flux density S 408 = 120 ± 30 mJy and 1.4 GHz flux density S 1400 = 79 ± 3 mJy. The H i structure of UGCA 86 is complex, with two separate components: a rotating disk and a highly elongated spur that is kinematically disjunct from the disk. The H i disk is centered on the optical galaxy with similar axial ratio and orientation of the major axis. An area of the disk with a peculiar velocity of ∼ 25 km s −1 relative to the regular rotation of the disk is found on the southern side, where most of the star formation is concentrated. The spur is seen along the minor axis of UGCA 86 and overlaps in part with the disk. Towards the – 2 – optical center of UGCA 86, the velocity difference between the spur and the disk is 40 km s −1 , about one third of the rotation velocity of the H i disk at 6 kpc from the center. This implies a large radial component of the orbital velocity of the spur, and therefore a significantly non-circular orbit. The median H i velocity dispersion of the disk is 8.8 km s −1 , similar to other (dwarf) galaxies. The H i velocity dispersion of the spur varies from 10 km s −1 to 30 km s −1. A possible tidal origin of the spur is considered in view of the proximity of the large Scd galaxy IC 342. However, the orientation of the spur along the minor axis and its spatial overlap with the disk suggest that the spur is located far outside the plane of the H i disk. No evidence is found that the outer H i disk is warped, which poses a problem for the interpretation of the spur as a tidal tail induced by IC 342. Detailed modelling of the IC 342/UGCA 86 system will be required before a tidal origin of the spur can be dismissed conclusively. The possibility that the spur is part of the nascent cloud of UGCA 86 or the remains of a small dwarf galaxy is presented as an alternative interpretation.