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Session 65 - ISM in Nearby Galaxies.
Oral session, Tuesday, January 16
Salon del Rey South, Hilton
While large-scale studies suggest that star formation has a weak dependence on density wave activity, detailed studies of individual galaxies (e.g., M51, M33) cast doubt on such conclusions. Do density waves have a significant influence on star formation, as compared to that of global parameters such as the average gas surface density? Flocculent galaxies are important counterexamples to grand design spirals: they exhibit weak, discontinuous spiral structure at optical wavelengths, suggesting the absence of a spiral density wave. A study of flocculent spirals, chosen to cover a range of gas surface densities, therefore offers the best means of isolating the effects of density waves on the formation of gas clouds and stars in spiral galaxies.
I have obtained observations of CO, HI, H\alpha, and near-infrared (NIR) broadband emission in a sample of four nearby flocculent spirals in order to characterize better the kinematics and star formation properties of flocculent galaxies. The NIR broadband data reveal low-level spiral structure in all four galaxies, suggesting the presence of weak density waves, while the CO observations reveal 10^6-10^7M_ødot cloud structures, similar to the Giant Molecular Associations detected in the grand design spiral M51. I will discuss the evidence for weak density waves in flocculent spirals and their relation to star and gas cloud formation, as well as the implications of this work for theories of spiral structure in galaxies.
