Probing the Interstellar Medium of the Superbubble LMC2 in the Large Magellanic Cloud. I. TI II and CA II Absorption Lines

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Abstract

The optical interstellar absorption lines of TiII and Ca II have been observed at high resolution toward seven OB supergiant stars in the Large Magellanic Cloud. The star lines of sight sample the disks and halos of both the Galaxy and the LMC, H I clouds in the LMC, and the filamentary super-structure of ionized gas known as the Superbubble LMC2 near the 30 Doradus nebula. We have measured the velocities, equivalent widths, column densities, and Doppler widths of Ca II and Ti II absorption lines detected over the whole range of velocities from - 30 to +360 km s^-1^ between the Galaxy and the LMC. There is interstellar absorption at velocities measured for the Hα emission-line gas of the superbubble and its surrounding giant H II regions and for the H I gas components toward this region of the LMC. Absorbing gas is also found at intermediate velocities between 150 and 220 km s^-1^, possibly identified with superbubble gas expanding into the LMC halo. The velocities above 150 km s^-1^ can be interpreted as three-dimensional motions of superbubble gas expanding in the surrounding medium in the framework of two existing representations of the large-scale distribution of H I LMC gas. The first picture consists of overlapping H I sheets at separate velocities; the interpretation of velocity components follows our previous kinematical study of the Hα LMC2 filaments. The second picture consists of two main components, the rotating LMC disk (D) and a lower velocity H I component (L); the correlations between Hα, H I, and absorption velocities suggest that LMC2 is expanding into the H I component L; perhaps its origin comes from cloud collisions between the components L and D. The remarkable extended absorption wings found between 150 and 220 km s^-1^ and the high-velocity absorption components at ~300 km s^-1^ are located in front of the H I components L and D; they prove the existence of upward and downward motions within the three-dimensional superbubble. Therefore, LMC2 is an example in which galactic fountains, superwinds, and falling high-velocity clouds participate in the complex dynamics of superbubbles.

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