Dust temperature is an important property of the interstellar medium ( ISM ) of galaxies .
It is required when converting ( sub ) millimeter broadband flux to total infrared luminosity ( L _ { IR } ) , and hence star formation rate , in high- z galaxies .
However , different definitions of dust temperatures have been used in the literature , leading to different physical interpretations of how ISM conditions change with , e.g . , redshift and star formation rate .
In this paper , we analyze the dust temperatures of massive ( M _ { star } > 10 ^ { 10 } M _ { \odot } ) z = 2 - 6 galaxies with the help of high-resolution cosmological simulations from the Feedback in Realistic Environments ( FIRE ) project .
At z \sim 2 , our simulations successfully predict dust temperatures in good agreement with observations .
We find that dust temperatures based on the peak emission wavelength increase with redshift , in line with the higher star formation activity at higher redshift , and are strongly correlated with the specific star formation rate .
In contrast , the mass-weighted dust temperature does not strongly evolve with redshift over z = 2 - 6 at fixed IR luminosity but is tightly correlated with L _ { IR } at fixed z .
The mass-weighted temperature is important for accurately estimating the total dust mass .
We also analyze an ‘ equivalent ’ dust temperature for converting ( sub ) millimeter flux density to total IR luminosity , and provide a fitting formula as a function of redshift and dust-to-gas ratio .
We find that galaxies of higher equivalent ( or higher peak ) dust temperature ( ‘ warmer dust ’ ) do not necessarily have higher mass-weighted temperatures .
A ‘ two-phase ’ picture for interstellar dust can explain the different scaling relations of the various dust temperatures .