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Wheels Of Fire. Iv: Star Formation And The Neutral Ism In The Ring Galaxy Am0644-741, James L. Higdon, Sarah J.U. Higdon

Department of Physics and Astronomy Faculty Publications

We combine data from the Australia Telescope National Facility and Swedish ESO Submillimeter Telescope to investigate the neutral interstellar medium (ISM) in AM0644-741, a large and robustly star-forming ring galaxy. The galaxy's ISM is concentrated in the 42 kpc diameter starburst ring, but appears dominated by atomic gas, with a global molecular fraction (f mol) of only 0.062 ± 0.005. Apart from the starburst peak, the gas ring appears stable against the growth of gravitational instabilities (Q gas = 3-11). Including the stellar component lowers Q overall, but not enough to make Q < 1 everywhere. High star formation efficiencies (SFEs) follow from the ring's low H2 content. AM0644-741's star formation law is highly peculiar: H I obeys a Schmidt law while H2 is uncorrelated with star formation rate density. Photodissociation models yield low volume densities in the ring, especially in the starburst quadrant (n 2 cm–3), implying a …