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D.J. Hanish, G.R. Meurer (Johns Hopkins University), H.C. Ferguson (Space Telescope Science Institute), M.A. Zwaan (European Southern Observatory), T.M. Heckman (Johns Hopkins University), SINGG Team
We have used H\alpha data from SINGG (the Survey for Ionization in Neutral Gas Galaxies) to measure the star formation rate density of local universe to be log(SFRD(0) [Msolar yr-1 Mpc-3]) = -1.77 + log(h70). The volume-averaged H\alpha equivalent width of our sample is found to be EW(H\alpha) = 29 Å, indicating that star formation in the SINGG galaxies is occurring at about one fourth of its past average rate. This confirms that star formation has drastically decreased in gas-rich galaxies since z ~1.5. We break down the H\alpha and R band luminosity densities in terms of the properties of the sample galaxies, including HI mass, stellar luminosity, dynamical mass, and surface brightness. A comparison of the dynamical masses of our galaxies with their stellar and HI masses shows significant evidence of downsizing: the most massive galaxies have a larger fraction of their mass locked up into stars than HI, while the opposite is true for less massive galaxies.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.