Gas motions and excitation in edge-on barred galaxies

Edge-on barred spiral galaxies show complex gas motions associated with gas flows around the bar.   There are two families of orbits around the bar (one faster and one slower). The edge-on bar is the peanut-shaped structure in the inner ± 20 arcsec of the galaxy.  In the bar region we see both orbit families, leading to a striking  cross or figure-of-eight pattern in the gas rotation curve. The figure shows an example (spectrum due to Martin Bureau).   In the upper image, the spectrograph slit is shown as the green line along the major axis of the galaxy.  The Hα spectrum in the lower image shows the two superimposed rotation components, on the same linear scale along the slit.

The emission line spectra of the gas in each orbit family is very different. This  could be due to different element abundances in the two families (with the inner orbit family significantly enriched in nitrogen), or to different gas excitation (possibly from shocks in gas moving in the inner orbit family).  A set of high resolution spectra from WiFeS is available for the best known example of such an edge-on barred galaxy,  taken to study this difference in the emission line spectra and determine its physical origin.  The goal of the project would be to analyse the spectra and determine the underlying reason for the different spectra of the two orbit families.

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