The history and future of the Local and Loop I bubbles

D. Breitschwerdt; M. A. de Avillez

doi:doi:10.1051/0004-6361:20064989

Free access

Issue		A&A Volume 452, Number 1, June II 2006


Page(s)		L1 - L5
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20064989

A&A 452, L1-L5 (2006)
DOI: 10.1051/0004-6361:20064989

Letter

The history and future of the Local and Loop I bubbles

D. Breitschwerdt¹ and M. A. de Avillez^{1, 2}

¹ Institut für Astronomie, Universität Wien, Türkenschanzstraße 17, 1180 Wien, Austria
e-mail: breitschwerdt@astro.univie.ac.at
² Department of Mathematics, University of Évora, R. Romão Ramalho 59, 7000 Évora, Portugal
e-mail: mavillez@galaxy.lca.uevora.pt

(Received 9 February 2006 / Accepted 30 March 2006 )

Abstract
Context.The Local and Loop I superbubbles are the closest and best investigated supernova (SN) generated bubbles and serve as test laboratories for observations and theories of the interstellar medium.
Aims.Since the morphology and dynamical evolution of bubbles depend on the ambient density and pressure distributions, a realistic modelling of the galactic environment is crucial for a detailed comparison with observations.
Methods.We have performed 3D high resolution (down to 1.25 pc on a kpc-scale grid) hydrodynamic simulations of the Local Bubble (LB) and the neighbouring Loop I (L1) superbubble in a realistically evolving inhomogeneous background ISM, disturbed already by SN explosions at the Galactic rate for 200 Myr before the LB and L1 are generated. The LB is the result of 19 SNe occurring in a moving group, which passed through the present day local HI cavity.
Results.We can reproduce (i) the OVI column density in absorption within the LB in agreement with COPERNICUS and recent FUSE observations, giving ${N}_{\rm OVI}<2 \times 10^{13} \, {\rm ~cm}^{-2}$ and ${N}_{\rm OVI}<7 \times 10^{12} \, {\rm cm}^{-2}$ , respectively; (ii) the observed sizes of the Local and Loop I superbubbles; (iii) the interaction shell between LB and L1, discovered with ROSAT; (iv) constrain the age of the LB to be $14.5\pm^{0.7}_{0.4}$ Myr; (v) predict the merging of the two bubbles in about 3 Myr, when the interaction shell starts to fragment; (vi) the generation of blobs like the Local Cloud as a consequence of a dynamical instability.
Conclusions.We find that evolving superbubbles strongly deviate from idealised self-similar solutions due to ambient pressure and density gradients, as well as due to turbulent mixing and mass loading. Hence, at later times the hot interior can break through the surrounding shell, which may also help to explain the puzzling energy "deficit" observed in LMC bubbles.

Key words: hydrodynamics -- shock waves -- ISM: general -- ISM: bubbles -- ISM: structure -- ISM: kinematics and dynamics

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