Characterizing Ultraviolet and Infrared Observational Properties for
  Galaxies. I. Influences of Dust Attenuation and Stellar Population Age
  The correlation between infrared-to-ultraviolet luminosity ratio and
ultraviolet color, i.e. the IRX-UV relation, was regarded as a prevalent recipe
for correcting extragalactic dust attenuation. Considerable dispersion in this
relation discovered for normal galaxies, however, complicates its usability. In
order to investigate the cause of the dispersion, in this paper, we select five
nearby spiral galaxies, and perform spatially resolved studies on each of the
galaxies, with a combination of ultraviolet and infrared imaging data. We
measure all positions within each galaxy and divide the extracted regions into
young and evolved stellar populations. By means of this approach, we attempt to
discover separate effects of dust attenuation and stellar population age on the
IRX-UV relation for individual galaxies. In this work, in addition to dust
attenuation, stellar population age is interpreted to be another parameter in
the IRX-UV function, and the diversity of star formation histories is suggested
to disperse the age effects. At the same time, strong evidence shows the
necessity of more parameters in the interpretation of observational data, such
as variations in attenuation/extinction law. Fractional contributions of
different components to the integrated luminosities of the galaxies suggest
that the integrated measurements of galaxies which comprise different
populations would weaken the effect of the age parameter on IRX-UV diagrams.
The dependance of the IRX-UV relation on luminosity and radial distance in
galaxies presents weak trends, which offers an implication of selective
effects. The two-dimensional maps of the UV color and the
infrared-to-ultraviolet ratio are displayed and show a disparity in the spatial
distributions between the two parameters in galaxies, which offers a spatial
interpretation of the scatter in the IRX-UV relation.
