  We present a demographic analysis of integrated star formation and gas
properties for a sample of galaxies representative of the overall population at
z~0. This research was undertaken in order to characterise the nature of star
formation and interstellar medium behaviour in the local universe, and test the
extent to which global star formation rates can be seen as dependent on the
interstellar gas content. Archival 21 cm derived HI data are compiled from the
literature, and are combined with CO (J=1-0) derived H_2 masses to calculate
and characterise the total gas content for a large sample of local galaxies.
The distribution in stellar mass-normalised HI content is found to exhibit the
noted characteristic transition at stellar masses of ~3x10^10 M_sun, turning
off towards low values, but no such transition is observed in the equivalent
distribution of molecular gas. H-alpha based star formation rates and specific
star formation rates are also compiled for a large (1110) sample of local
galaxies. We confirm two transitions as found in previous work: a turnover
towards low SFRs at high luminosities, indicative of the quenching of SF
characteristic of the red sequence; and a broadening of the SF distribution in
low-luminosity dwarf galaxies, again to extremely low SFRs of < 0.001 M_sun/yr.
However, a new finding is that while the upper luminosity transition is
mirrored by the turn over in HI content, suggesting that the low SFRs of the
red sequence result from a lack of available gas supply, the transition towards
a large spread of SFRs in the least luminous dwarf galaxies is not matched by a
prominent increase in scatter in gas content. Possible mass-dependent quenching
mechanisms are discussed, along with speculations that in low mass galaxies,
the H-alpha luminosity may not faithfully trace the SFR.
