APEX observations of supernova remnants - I. Non-stationary MHD-shocks in W44

Abstract

Aims. The interaction of supernova remnants (SNRs) with molecular clouds gives rise to strong molecular emission in the far-IR and sub-mm wavelength regimes. The application of MHD shock models in the interpretation of this line emission can yield valuable information on the energetic and chemical impact of supernova remnants. Methods. New mapping observations with the APEX telescope in CO (3-2), (4-3), (6-5), (7-6) and 13CO (3-2) towards two regions in the supernova remnant W44 are presented. Integrated intensities are extracted on five different positions, corresponding to local maxima of CO emission. The integrated intensities are compared to the outputs of a grid of models, which combine an MHD shock code with a radiative transfer module based on the large velocity gradient approximation. Results. All extracted spectra show ambient and line-of-sight components as well as blue- and red-shifted wings indicating the presence of shocked gas. Basing the shock model fits only on the highest-lying transitions that unambiguously trace the shock-heated gas, we find that the observed CO line emission is compatible with non-stationary shocks and a pre-shock density of 10^4 cm-3. The ages of the modelled shocks scatter between values of \sim1000 and \sim3000 years. The shock velocities in W44F are found to lie between 20 and 25 km/s, while in W44E fast shocks (30-35 km/s) as well as slower shocks (\sim20 km/s) are compatible with the observed spectral line energy diagrams. The pre-shock magnetic field strength components perpendicular to the line of sight in both regions have values between 100 and 200 \muG. Our best-fitting models allow us to predict the full ladder of CO transitions, the shocked gas mass in one beam as well as the momentum- and energy injection.

20 pages, 13 figures, 13 tables, accepted for publication in Astronomy and Astrophysics

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• Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
• Spitzer spectral line mapping of supernova remnants: I. Basic data and principal component analysis
• The low frequency radio emission and spectrum of the extended SNR W44: new VLA observations at 74 and 324 MHz
• APECS - The Atacama Pathfinder Experiment Control System
• Shocks in dense clouds. IV. Effects of grain-grain processing on molecular line emission

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• Discovery of a Wind-Blown Bubble Associated with the Supernova Remnant G346.6-0.2: A Hint for the Origin of Recombining Plasma
• Discovery of Broad Molecular lines and of Shocked Molecular Hydrogen from the Supernova Remnant G357.7+0.3: HHSMT, APEX, Spitzer and SOFIA Observations
• Submillimeter observations of molecular gas interacting with the supernova remnant W28
• The shocked gas of the BHR71 outflow observed by Herschel: indirect evidence for an atomic jet
• Shocked Molecular Hydrogen and Broad CO lines from the Interacting Supernova Remnant HB 3
• Supernova Shocks in Molecular Clouds: Shocks Driven into Dense Cores in IC 443 and 3C 391
• Revealing the drag instability in one-fluid nonideal MHD simulations of a 1D isothermal C-shock