Observing the host galaxies of high-redshift quasars with JWST: predictions from the BlueTides simulation

TL;DR

This study uses simulations to predict JWST's ability to detect high-redshift quasar host galaxies, showing that JWST will significantly outperform HST in this task, especially with specific observational strategies.

Contribution

The paper provides the first detailed predictions of JWST's capability to observe quasar host galaxies at z=7 using mock images from the BlueTides simulation.

Findings

JWST NIRCam can detect ~50% of quasar hosts at z=7.

Wide-band long-wavelength filters optimize host galaxy detection.

Exposure times of ~5 ks are sufficient for most detections.

Abstract

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.