# Predictions for deep galaxy surveys with JWST from $\Lambda$CDM

## TL;DR

This paper uses a physical galaxy formation model within the $\\Lambda$CDM framework to predict galaxy observations with JWST, including luminosity functions, counts, and sizes across redshifts, validated against existing data.

## Contribution

It provides the first comprehensive predictions for JWST galaxy surveys based on a calibrated, physically motivated galaxy formation model covering high redshifts up to 16.

## Key findings

- Predicts ~1 galaxy per JWST field at z~11 with 10^4 s exposure.
- Higher reionization redshift model predicts 5x more galaxies at z~11.
- MIRI is unlikely to detect galaxies beyond z~6.

## Abstract

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 $M_{\rm halo}>2\times10^{9}$ $h^{-1}$ 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 $z\lesssim6$, and we show here that it can also predict evolution of the rest-frame far-UV luminosity function for $7\lesssim z\lesssim10$ 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 $z\sim11$ 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 $\sim5\times$ greater at this redshift. Similar observations with MIRI are predicted not to detect any galaxies at $z\gtrsim6$. 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.