High redshift JWST predictions from IllustrisTNG: III. Infrared luminosity functions, obscured star formation and dust temperature of high-redshift galaxies

Kavli Affiliate: Mark Vogelsberger

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| Summary:

We post-process galaxies in the IllustrisTNG simulations with SKIRT radiative
transfer calculations to make predictions for the rest-frame near-infrared
(NIR) and far-infrared (FIR) properties of galaxies at $zgeq 4$. The
rest-frame $K$- and $z$-band galaxy luminosity functions from TNG are overall
consistent with observations, despite a $sim 0.5,mathrm{dex}$
underprediction at $z=4$ for $M_{rm K}lesssim -25$ and $M_{rm z}lesssim
-24$. Predictions for the JWST MIRI observed galaxy luminosity functions and
number counts are given. Based on theoretical estimations, we show that the
next-generation survey conducted by JWST can detect 500 (30) galaxies in F1000W
in a survey area of $500,{rm arcmin}^{2}$ at $z=6$ ($z=8$). As opposed to the
consistency in the UV, optical and NIR, we find that TNG, combined with our
dust modelling choices, significantly underpredicts the abundance of most
dust-obscured and thus most luminous FIR galaxies. As a result, the obscured
cosmic star formation rate density (SFRD) and the SFRD contributed by
optical/NIR dark objects are underpredicted. The discrepancies discovered here
could provide new constraints on the sub-grid feedback models, or the dust
contents, of simulations. Meanwhile, although the TNG predicted dust
temperature and its relations with IR luminosity and redshift are qualitatively
consistent with observations, the peak dust temperature of $zgeq 6$ galaxies
are overestimated by about $20,{rm K}$. This could be related to the limited
mass resolution of our simulations to fully resolve the porosity of the
interstellar medium (or specifically its dust content) at these redshifts.

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