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

Madeline A. Marshall, J. Stuart B. Wyithe, Rogier A. Windhorst, Tiziana Di Matteo, Yueying Ni, Stephen Wilkins, Rupert A. C. Croft, Mira Mechtley

Published 2021-01-04Version 1

The bright emission from high-redshift quasars completely conceals their host galaxies in the rest-frame UV/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 find 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 underestimates the Sersic magnitudes of the host galaxies due to residual flux from the quasar contaminating the central core, which also results in a slight underestimation of the Sersic radii and significant overestimation of the Sersic indices n. Care should be made when interpreting the host properties measured using PSF modelling.