Galaxies SIG Seminar

Simulations Meet Space Telescopes to Understand AGN at Cosmic Dawn

Speaker

Sabrina Berger (University of Melbourne)

Abstract

For the first time, JWST lets us directly see the stellar light from galaxies hosting luminous quasars at z > 6. Early stellar mass estimates often suggest black hole to stellar mass ratios far higher than those observed locally, but quasar emission can contribute more than 95% of the observed light and dramatically amplify measurement uncertainties. To address this, I developed a Bayesian framework that uses forward-modeled mock observations from hydrodynamic simulations to quantify observational biases in high-z quasar host stellar mass estimates. I find that host masses can often be recovered, but with occasional misestimates that may push inferred black hole growth even further from local relations. Lastly, I’ll discuss how high-z quasar hosts function like pseudo-extragalactic exoplanets for HWO, with faint host light buried under a bright quasar and recovery limited by contrast, resolution, and PSF stability. Constraining these biases is central to a unified picture of early black hole and galaxy co-evolution, and HWO’s capabilities in this regime will deliver stronger AGN host constraints and mitigate observational biases that currently limit JWST.

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