Calibration of the total infrared luminosity of nearby galaxies from
  Spitzer and Herschel bands
  We present new empirical calibrations to estimate resolved and integrated
total infrared luminosities from Spitzer and Herschel bands used as
monochromatic or combined tracers. We base our calibrations on resolved
elements of nearby galaxies (3 to 30 Mpc) observed with Herschel. We perform a
resolved SED modelling of these objects using the Draine and Li (2007) dust
models and investigate the influence of the addition of SPIRE measurements in
the estimation of LTIR. We find that using data up to 250 um leads to local
LTIR values consistent with those obtained with a complete coverage (up to 500
um) within 10 per cent for most of our resolved elements. We then study the
distribution of energy in the resolved SEDs of our galaxies. The bulk of energy
(30-50 per cent) is contained in the (70-160 um) band. The (24-70 um) fraction
decreases with increasing metallicity. The (160-1100 um) submillimeter band can
account for up to 25 per cent of the LTIR in metal-rich galaxies. We
investigate the correlation between TIR surface brightnesses/luminosities and
monochromatic Spitzer and Herschel surface brightnesses/luminosities. The three
PACS bands can be used as reliable monochromatic estimators of the LTIR, the
100 um band being the most reliable monochromatic tracer. There is also a
strong correlation between the SPIRE 250um and LTIR, although with more scatter
than for the PACS relations. We also study the ability of our monochromatic
relations to reproduce integrated LTIR of nearby galaxies as well as LTIR of
z=1-3 sources. Finally, we provide calibration coefficients that can be used to
derive TIR surface brightnesses/luminosities from a combination of Spitzer and
Herschel surface brightnesses/fluxes and analyse the associated uncertainties.
