Spectral Energy Distribution ( SED ) fitting in the far-infrared ( FIR ) is greatly limited by a dearth of data and an excess of free parameters - from galaxies ’ dust composition , temperature , mass , orientation , opacity , to heating from Active Galactic Nuclei ( AGN ) .
This paper presents a simple FIR SED fitting technique joining a modified , single dust temperature greybody , representing the reprocessed starburst emission in the whole galaxy , to a mid-infrared powerlaw , which approximates hot-dust emission from AGN heating or clumpy , hot starbursting regions .
This FIR SED can be used to measure infrared luminosities , dust temperatures and dust masses for both local and high- z galaxies with 3 to 10+ FIR photometric measurements .
While the fitting technique does not model emission from polycyclic aromatic hydrocarbons ( PAHs ) in the mid-infrared , the impact of PAH features on integrated FIR properties is negligible when compared to the bulk emission at longer wavelengths .

This fitting method is compared to infrared template SEDs in the literature using photometric data on 65 local luminous and ultraluminous infrared galaxies , ( U ) LIRGs .
Despite relying only on 2–4 free parameters , the coupled greybody/powerlaw SED fitting described here produces better fits to photometric measurements than best-fit literature template SEDs ( with residuals a factor of \sim 2 lower ) .
A mean emissivity index of \beta =1.60 \pm 0.38 and mid-infrared powerlaw slope of \alpha =2.0 \pm 0.5 is measured ; the former agrees with the widely presumed emissivity index of \beta =1.5 and the latter is indicative of an optically-thin dust medium with a shallow radial density profile , \approx r ^ { -1 / 2 } .
Adopting characteristic dust temperature as the inverse wavelength where the SED peaks , dust temperatures \sim 25–45 K are measured for local ( U ) LIRGs , \sim 5–15 K colder than previous estimates using only simple greybodies .
This comparative study highlights the impact of SED fitting assumptions on the measurement of physical properties such as infrared luminosity ( and thereby infrared-based star formation rate ) , dust temperature and dust mass , for both local and high-redshift galaxies .