Mid and Far-Infrared Color-Color Relations within Local Galaxies
  We present an extensive archival analysis of a sample of local galaxies,
combining multi-wavelength data from GALEX, Spitzer and Herschel to investigate
"blue-side" mid-infrared (MIR) and "red-side" far-infrared (FIR) color-color
correlations within the observed infrared spectral energy distributions (IR
SEDs). Our sample largely consists of the KINGFISH galaxies, with the important
addition of a select few including NGC5236 (M83) and NGC4449. With data from
the far-ultraviolet FUV (${\sim}0.15$ $\mu$m) through 500 $\mu$m convolved to
common angular resolution, we measure photometry of $kpc$-scale star-forming
regions 36$"\times$36$"$ in size. Star formation rates (SFRs), stellar masses
and metallicity distributions are derived throughout our sample. Focusing on
the $f_{70}/f_{500}$ "FIR" and $f_{8}/f_{24}$ "MIR" flux density ratios
(colors), we find that a sub-sample of galaxies demonstrate a strong IR
color-color correlation within their star-forming regions, while others
demonstrate uncorrelated colors. This division is driven by two main effects:
1) the local strength of star formation (SF) and 2) the metal content of the
interstellar medium (ISM). Galaxies uniformly dominated by high surface
densities of SF (e.g. NGC5236) demonstrate strong IR color-color correlations,
while galaxies that exhibit lower levels of SF and mixed environments (e.g.
NGC5457) demonstrate weaker or no correlation--explained by the increasing
effect of varying ISM heating and metal content on the IR colors, specifically
in the MIR. We find large dispersion in the SFR-$L_{8}$ (8 $\mu$m luminosity)
relation that is traced by the metallicity distributions, consistent with
extant studies, highlighting its problematic use as a SFR indicator across
diverse systems/samples.
