The Kinematic Map of the Ionized Gas of the Supergiant Shell LMC SGS 2

A complete kinematic map of much of the supergiant shell LMC SGS 2 has been established by scanning Fabry-Pérot observations at Hα wavelength. We present velocity determinations for this large-diameter supergiant shell. We confirm some motions already observed by other authors in previous local interferometric and spectrographic observations. However, our results give a better insight into the whole kinematics of this supergiant shell because of our complete spatial coverage of the two-dimensional velocities. We find that no global expansion pattern is present in this supergiant shell. On the contrary, we find line-splitting of the velocity profile even outside the filamentary boundaries of LMC SGS 2. Indeed, we detect faint Hα diffuse emission as far as ~6' outside the long filaments of the boundary of the supershell, with several velocity components. We also find that the outermost northern filament displays two velocity components (also contradicting a simple radial expansion of the shell), while the filamentary boundary to the east occasionally has a faint secondary velocity component. Inside the supergiant shell, the diffuse emission at the center of LMC SGS 2 is the most coherent, while some interior filaments display two velocity components. The velocity pattern found agrees more with two gas layers seen projected along the same line of sight, with local expansions of small wind bubbles formed by stellar associations inside to LMC SGS 2.

Based on observations done at La Silla (ESO), Chile.