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Register a new userHigh redshift JWST predictions from IllustrisTNG: Dust modelling and galaxy luminosity functions
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Mark Vogelsberger
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The James Webb Space Telescop (JWST) promises to revolutionise our understanding of the early Universe, and contrasting its upcoming observations with predictions of the $Lambda$CDM model requires detailed theoretical forecasts. Here, we exploit the large dynamic range of the IllustrisTNG simulation suite, TNG50, TNG100, and TNG300, to derive multi-band galaxy luminosity functions from $z=2$ to $z=10$. We put particular emphasis on the exploration of different dust attenuation models to determine galaxy luminosity functions for the rest-frame ultraviolet (UV), and apparent wide NIRCam bands. Our most detailed dust model is based on continuum Monte Carlo radiative transfer calculations employing observationally calibrated dust properties. This calibration results in constraints on the redshift evolution of the dust attenuation normalisation and dust-to-metal ratios yielding a stronger redshift evolution of the attenuation normalisation compared to most previous theoretical studies. Overall we find good agreement between the rest-frame UV luminosity functions and observational data for all redshifts, also beyond the regimes used for the dust-model calibrations. Furthermore, we also recover the observed high redshift ($z=4-6$) UV luminosity versus stellar mass relation, the H$alpha$ versus star formation rate relation, and the H$alpha$ luminosity function at $z=2$. The bright end ($M_{rm UV}>-19.5$) cumulative galaxy number densities are consistent with observational data. For the F200W NIRCam band, we predict that JWST will detect $sim 80$ ($sim 200$) galaxies with a signal-to-noise ratio of $10$ ($sim 5$) within the NIRCam field of view, $2.2times2.2 ,{rm arcmin}^{2}$, for a total exposure time of $10^5{rm s}$ in the redshift range $z=8 pm 0.5$. These numbers drop to $sim 10$ ($sim 40$) for an exposure time of $10^4{rm s}$.
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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 $sim 0.4,mathrm{dex}$ underprediction at $z=4$ for $M_{rm z}lesssim -24$. Predictions for the JWST MIRI observed galaxy luminosity functions and number counts are given. 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.
We present predictions for high redshift ($z=2-10$) galaxy populations based on the IllustrisTNG simulation suite and a full Monte Carlo dust radiative transfer post-processing. Specifically, we discuss the ${rm H}_{alpha}$ and ${rm H}_{beta}$ + $[rm O ,III]$ luminosity functions up to $z=8$. The predicted ${rm H}_{beta}$ + $[rm O ,III]$ luminosity functions are consistent with present observations at $zlesssim 3$ with $lesssim 0.1,{rm dex}$ differences in luminosities. However, the predicted ${rm H}_{alpha}$ luminosity function is $sim 0.3,{rm dex}$ dimmer than the observed one at $zsimeq 2$. Furthermore, we explore continuum spectral indices, the Balmer break at $4000$AA (D4000) and the UV continuum slope $beta$. The median D4000 versus sSFR relation predicted at $z=2$ is in agreement with the local calibration despite a different distribution pattern of galaxies in this plane. In addition, we reproduce the observed $A_{rm UV}$ versus $beta$ relation and explore its dependence on galaxy stellar mass, providing an explanation for the observed complexity of this relation. We also find a deficiency in heavily attenuated, UV red galaxies in the simulations. Finally, we provide predictions for the dust attenuation curves of galaxies at $z=2-6$ and investigate their dependence on galaxy colors and stellar masses. The attenuation curves are steeper in galaxies at higher redshifts, with bluer colors, or with lower stellar masses. We attribute these predicted trends to dust geometry. Overall, our results are consistent with present observations of high redshift galaxies. Future JWST observations will further test these predictions.
The bright emission from high-redshift quasars completely conceals their host galaxies in the rest-frame ultraviolet/optical, with detection of the hosts in these wavelengths eluding even the Hubble Space Telescope (HST) using detailed point spread function (PSF) modelling techniques. In this study we produce mock images of a sample of z=7 quasars extracted from the BlueTides simulation, and apply Markov Chain Monte Carlo-based PSF modelling to determine the detectability of their host galaxies with the James Webb Space Telescope (JWST). While no statistically significant detections are made with HST, we predict that at the same wavelengths and exposure times JWST NIRCam imaging will detect ~50% of quasar host galaxies. We investigate various observational strategies, and find that NIRCam wide-band imaging in the long-wavelength filters results in the highest fraction of successful quasar host detections, detecting >80% of the hosts of bright quasars in exposure times of 5 ks. Exposure times of ~5 ks are required to detect the majority of host galaxies in the NIRCam wide-band filters, however even 10 ks exposures with MIRI result in <30% successful host detections. We find no significant trends between galaxy properties and their detectability. The PSF modelling can accurately recover the host magnitudes, radii, and spatial distribution of the larger-scale emission, when accounting for the central core being contaminated by residual quasar flux. Care should be made when interpreting the host properties measured using PSF modelling.
We present predictions for the outcome of deep galaxy surveys with the $James$ $Webb$ $Space$ $Telescope$ ($JWST$) obtained from a physical model of galaxy formation in $Lambda$CDM. We use the latest version of the GALFORM model, embedded within a new ($800$ Mpc)$^{3}$ dark matter only simulation with a halo mass resolution of $M_{rm halo}>2times10^{9}$ $h^{-1}$ M$_{odot}$. For computing full UV-to-mm galaxy spectral energy distributions, including the absorption and emission of radiation by dust, we use the spectrophotometric radiative transfer code GRASIL. The model is calibrated to reproduce a broad range of observational data at $zlesssim6$, and we show here that it can also predict evolution of the rest-frame far-UV luminosity function for $7lesssim zlesssim10$ which is in good agreement with observations. We make predictions for the evolution of the luminosity function from $z=16$ to $z=0$ in all broadband filters on the Near InfraRed Camera (NIRCam) and Mid InfraRed Instrument (MIRI) on $JWST$ and present the resulting galaxy number counts and redshift distributions. Our fiducial model predicts that $sim1$ galaxy per field of view will be observable at $zsim11$ for a $10^4$ s exposure with NIRCam. A variant model, which produces a higher redshift of reionization in better agreement with $Planck$ data, predicts number densities of observable galaxies $sim5times$ greater at this redshift. Similar observations with MIRI are predicted not to detect any galaxies at $zgtrsim6$. We also make predictions for the effect of different exposure times on the redshift distributions of galaxies observable with $JWST$, and for the angular sizes of galaxies in $JWST$ bands.
We present galaxy luminosity functions at 3.6, 4.5, 5.8, and 8.0 micron measured by combining photometry from the IRAC Shallow Survey with redshifts from the AGN and Galaxy Evolution Survey of the NOAO Deep Wide-Field Survey Bootes field. The well-defined IRAC samples contain 3800-5800 galaxies for the 3.6-8.0 micron bands with spectroscopic redshifts and z < 0.6. We obtained relatively complete luminosity functions in the local redshift bin of z < 0.2 for all four IRAC channels that are well fit by Schechter functions. We found significant evolution in the luminosity functions for all four IRAC channels that can be fit as an evolution in M* with redshift, Delta M* = Qz. While we measured Q=1.2pm0.4 and 1.1pm0.4 in the 3.6 and 4.5 micron bands consistent with the predictions from a passively evolving population, we obtained Q=1.8pm1.1 in the 8.0 micron band consistent with other evolving star formation rate estimates. We compared our LFs with the predictions of semi-analytical galaxy formation and found the best agreement at 3.6 and 4.5 micron, rough agreement at 8.0 micron, and a large mismatch at 5.8 micron. These models also predicted a comparable Q value to our luminosity functions at 8.0 micron, but predicted smaller values at 3.6 and 4.5 micron. We also measured the luminosity functions separately for early and late-type galaxies. While the luminosity functions of late-type galaxies resemble those for the total population, the luminosity functions of early-type galaxies in the 3.6 and 4.5 micron bands indicate deviations from the passive evolution model, especially from the measured flat luminosity density evolution. Combining our estimates with other measurements in the literature, we found (53pm18)% of the present stellar mass of early-type galaxies has been assembled at z=0.7.
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