Calibration of the total infrared luminosity of nearby galaxies from Spitzer and Herschel bands

Abstract

When combined with infrared observations with the Spitzer telescope (3 to 160 mu m), the Herschel Space Observatory now fully samples the thermal dust emission up to 500 mu m and enables us to better estimate the total infrared-submm energy budget (L-TIR) of nearby galaxies. 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 spectral energy distribution (SED) modelling of these objects using the Draine & Li dust models and investigate the influence of the addition of Spectral and Photometric Imaging Receiver (SPIRE) measurements in the estimation of L-TIR. We find that using data up to 250 mu m leads to local L-TIR values consistent with those obtained with a complete coverage (up to 500 mu m) 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 mu m] band. The [24-70 mu m] fraction decreases with increasing metallicity. The [160-1100 mu m] submillimetre band can account for up to 25 per cent of the L-TIR in metal-rich galaxies. We investigate the correlation between the total infrared (TIR) surface brightnesses/luminosities and monochromatic Spitzer and Herschel surface brightnesses/luminosities. The three Photodetector Array Camera and Spectrometer (PACS) bands can be used as reliable monochromatic estimators of the L-TIR, the 100 mu m band being the most reliable monochromatic tracer. There is also a strong correlation between the SPIRE 250 mu m and L-TIR, although with more scatter than for the PACS relations. We also study the ability of our monochromatic relations to reproduce integrated L-TIR of nearby galaxies as well as L-TIR of z similar to 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.