Shock Tracers Research Articles

Sulphur-bearing molecules as tracers of shocks in interstellar clouds

We have computed two-fluid MHD models of shocks propagating in molecular clouds of density 104≤ nH≤ 106 cm–3, with speeds of 5 ≤ υs ≤ 40 km s–1. Attention has been paid to the chemistry of sulphur-bearing species, particularly SO, SO2, CS and H2S. We find that the fractional abundance of H2S is enhanced within the shock, whilst those of SO and especially SO2 can be enhanced both within the shock and for large distances (up to 1018 cm) into the post-shock gas. The fractional abundance of CS, on the other hand, remains roughly constant. The relevance of these results to observations of outflows in molecular clouds is mentioned.

Infrared Observations of Interstellar Molecular Hydrogen

Emission from vibrationally excited molecular hydrogen has been detected from a wide range of astronomical targets during the last decade (e.g. Shull and Beckwith 1982). in all cases the H2has been shock excited, and we have grown accustomed to the idea that H2is a useful tracer of interstellar shocks.

Gas dynamics in barred spirals - Gaseous density waves and galactic shocks

Steady-state gasdynamical studies, previously limited to tightly wound normal spiral galaxies, are extended to models of barred spirals with a 5% to 10% perturbing potential. The models show that a strong wave manifestation is an important constituent of the bar structure in many barred spirals and that a density-wave shock wave can form a bar structure as pronounced as the narrow bars often evident in optical photographs of barred spirals. The dark narrow dust lanes often observed along the leading edges of bar structures are identified as tracers of shocks, and it is found that strong shocks along a bar structure during even a small part of a galaxy's lifetime might easily deplete a large enough proportion of the gas to cause a lack of gas in the inner annuli encompassing the bar by the time of the present epoch. It is emphasized that even moderate-amplitude barlike perturbations in the disk can drive large noncircular gas motions, typically 50 to 150 km/s.