We present the first study of GALEX far ultra-violet (FUV) luminosity
functions of individual star-forming regions within a sample of 258 nearby
galaxies spanning a large range in total stellar mass and star formation
properties. We identify ~65,000 star-forming regions (i.e., FUV sources),
measure each galaxy's luminosity function, and characterize the relationships
between the luminosity function slope (alpha) and several global galaxy
properties. A final sample of 82 galaxies with reliable luminosity functions
are used to define these relationships and represent the largest sample of
galaxies with the largest range of galaxy properties used to study the
connection between luminosity function properties and galaxy environment. We
find that alpha correlates with global star formation properties, where
galaxies with higher star formation rates and star formation rate densities
(Sigma_SFR) tend to have flatter luminosity function slopes. In addition, we
find that neither stochastic sampling of the luminosity function in galaxies
with low-number statistics nor the effects of blending due to distance can
fully account for these trends. We hypothesize that the flatter slopes in high
Sigma_SFR galaxies is due to higher gas densities and higher star formation
efficiencies which result in proportionally greater numbers of bright
star-forming regions. Finally, we create a composite luminosity function
composed of star-forming regions from many galaxies and find a break in the
luminosity function at brighter luminosities. However, we find that this break
is an artifact of varying detection limits for galaxies at different distances.Science and Technology Facilities CouncilThis is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw169
