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G. R. Petitpas, C. D. Wilson (McMaster University)
It is known that bars in galaxies are a good way of transporting disk material inwards towards the nucleus where it may fuel starburst or AGN activity. Models show that the material can only be transported in to the Inner Lindblad Resonance (ILR), where it may get trapped, forming a nuclear ring or `twin-peaked' galaxy. To overcome this, Shlosman, Frank, & Begelman (1989) proposed a mechanism where a secondary bar may form inside the ILR radius, allowing material to be transported further inward.
This paper presents high resolution CO J=1-0 observations of barred galaxies containing NIR isophote twists, thought to be the signature of the secondary bar inside the ILR radius. We show that the CO distribution does not always exhibit the double-barred morphology as predicted by simulations of these systems. This result suggests that in some systems the NIR isophote twists are the result of a triaxial stellar bulge (as predicted by Kormendy 1979) and that in general NIR images are not a reliable way of detecting double-barred systems.
We will also discuss the results of a CO J=2-1 survey of all galaxies containing NIR isophote twists visible from the northern hemisphere that suggests that these galaxies may be underluminous in CO (at least at the lower J transitions). This is contrary to computer simulations of these galaxies which suggests that they need to be gas rich in order to maintain the observed morphology. We also present preliminary multi-line CO data taken at the JCMT which suggest that the `true' double-barred galaxies (as indicated by the CO maps) tend to contain warmer gas in the nucleus. This could explain the missing CO J=2-1 emission if the gas is warm enough that most of the CO emission in emitted at the higher J transitions.
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The author(s) of this abstract have provided an email address for comments about the abstract: petitpa@physics.mcmaster.ca