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Astron. Astrophys. 358, 299-309 (2000)

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The kinematical characteristics of the CNM at [FORMULA] and the hypothesis of a local explosive event

W.G.L. Pöppel * and P. Marronetti  **

Instituto Argentino de Radioastronomía, Casilla de Correo 5, 1894 Villa Elisa, B.A., Argentina (wpoppel@iar.unlp.edu.ar; pedro@galileo.ph.utexas.edu)

Received 11 October 1999 / Accepted 25 February 2000


We computed ballistic positions and velocities for test particles, which were ejected a time [FORMULA] ago, from a small volume at a mean altitude [FORMULA] above the galactic plane at a distance r. The results were fitted to the peaks detected in the residual HI-profiles of observations of the cold neutral medium (CNM) derived from HI-atlases in a former paper. At low latitudes, a significant fraction of the observations is fitted, either by the ballistic model or by Olano's (1982) accretion model for an expanding ring of gas. Another large fraction of the observations corresponds to relatively distant objects, which appear to be mainly in galactic differential rotation. At intermediate and high latitudes the fit by the ballistic model appears to be rather satisfactory for the bulk of the observations. The test particles ejected toward northern altitudes larger than about [FORMULA] have no observational counterparts but fit an area on the sky, which roughly encloses the well-known northern HI-hole. We suggest that this could be a signature of the explosive event indicating the ionization and transfer of gas into the lower halo.

The fit is less satisfactory for the CNM in the large Sco-Cen shells and the Ori-Eri bubble. Since these regions were affected by star-formation processes after the assumed explosive event, we included young disturbance centers in the models, producing isotropic radial accelerations on the affected test particles. This improved the fit significantly. A sample of positions on the high-velocity cloud complex M could be fitted by assuming particles ejected at high velocities with altitudes larger than [FORMULA]. We conclude that the assumption of an explosive event with [FORMULA] Myr, [FORMULA] pc and [FORMULA] pc in the direction of galactic longitude [FORMULA], appears to be consistent with the observed kinematics of a large deal of the local CNM.

Key words: ISM: clouds – ISM: kinematics and dynamics – Galaxy: solar neighbourhood

* Member of Carrera del Investigador Científico, CONICET
** now at Center for Relativity, Department of Physics, University of Texas at Austin, Austin, TX 78712, USA

Send offprint requests to: W.G.L. Pöppel

© European Southern Observatory (ESO) 2000

Online publication: June 26, 2000