The neutral hydrogen sheets and supergiant shells of the Large Magellanic Cloud

Abstract

Profiles of the 21-cm H <scp>I</scp> emission line have been obtained with high signal-to-noise ratios at 0°.5 intervals along three long tracks which intersect supergiant shells of the Large Magellanic Cloud. The half-power beam width was 14.85 arcmin. Along one of the tracks, evidence is found of extensive overlapping sheets of H <scp>I</scp>, 1–3 kpc across, with different radial velocities. Profiles from the centre of the largest supergiant shell LMC4 are broad, and faint components with <f>$\\simeq - 160 \\,\\text{km s} ^{-1}$</f> radial velocity difference with respect to the LMC plane are found over LMC3, 7 and 8. Profiles with ±100 km s–1 wings are present near LMC3, 7 and 8. No evidence has been found that any of the supergiant shells are radially expanding, spherical, structures, although this may be a consequence of the large sampling interval and large HPBW of the telescope. We estimate that the extensive H <scp>I</scp> sheets have a total kinetic energy <f>$\\simeq 4.5 \\times 10^{54}$</f> erg in their motion away from the H <scp>I</scp> in the plane of the LMC. This could be supplied by supernovae and stellar winds over <f>$2 \\times 10^{7} \\text{yr}.$</f> It is interesting that tidal disruption of the LMC by the Galaxy could produce stellar motions similar to those observed in the H <scp>I</scp> sheets, but it is not clear how the sheets could form in this way. The very-high-velocity components in the vicinity of supergiant shells have kinetic energies of <f>$\\simeq 10 ^{52}$</f> erg with respect to the plane of the LMC. This energy is easily provided by a few supernovae or by stellar winds.