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Astron. Astrophys. 325, 961-971 (1997)

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3. Observational data

From the literature we compiled inclination corrected data on H I mass surface density, velocity integrated CO intensity, and H [FORMULA] surface brightness, with the latter being considered proportional to the SFR. The H [FORMULA] line is produced by recombination in H II region ionized by the Lyman-continuum radiation of hot stars, and can thus be considered a most reliable measure of massive star formation (Kennicutt 1983a). If not all stellar photons are absorbed in the H II region gas, this may lead to an underestimation of the SFR (cf. Patel & Wilson 1995a).

The CO brightnesses are converted into H2 mass surface densities by the same factor for all the galaxies: [FORMULA] in accordance with Gordon & Burton (1976), whose data is used in Smith et al. (1978). Usually CO was measured only in a smaller, interior portion of the disk for which H [FORMULA] -data is available. Then we consider only that part of the disk for which both data are available. The mass surface density of all the gas is obtained from that of hydrogen by multiplication of a factor 1.4, to account for a helium fraction of ten per cent (by number). All the data is linearly interpolated onto the grid given by the H [FORMULA] data.

We do not wish to make any further selection of the data which might reflect some underlying prejudice. Hence, we include all points, for which all three data are available. In the following we give the references and notes for individual galaxies. The types are from Sandage & Tammann (1981):

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998