Observations of Early Black Holes Before and After JWST

Abstract

These notes are from three lectures given at the 54th Saas-Fee Advanced Course of the Swiss Society of Astrophysics and Astronomy in January 2025. This chapter reviews the dramatic evolution in our understanding of supermassive black holes in the first billion years, from ground-based discoveries to recent space-based infrared observations with JWST. Section 1 introduces AGN and quasars to contextualise observations at the highest redshifts. Section 2 reviews the pre-JWST understanding of early quasars, including personal accounts of how key discoveries were made. Section 3 examines how JWST is transforming the field, from black hole mass measurements and host galaxy characterisation to large-scale environmental studies, and identifies emerging directions.

Figures (33)

• Figure 1: ChatGPT's comparison table generated in response to the prompt "What is the difference between AGN and quasars?" The AI correctly identifies luminosity as the primary distinction. Note that the "Distance" entry was accurate before JWST observations but has since been superseded by recent discoveries.
• Figure 2: Practical luminosity boundaries for classifying AGN and quasars. The coloured regions indicate approximate divisions based on the UV absolute magnitude $M_{1450}$ (top axis) and bolometric luminosity (bottom axis), with the conversion between the two axes following runnoe2012. The black curve illustrates the typical luminosity distribution. While these boundaries are somewhat arbitrary, they provide useful guidance for the literature, where classification schemes often vary between studies.
• Figure 3: Maarten Schmidt's original observing log that resulted in the now famous discovery of the first quasar 3C 273 schmidt1963. This photo was taken in 2016 at the Carnegie Observatories' basement vault.
• Figure 4: Schematic spectral energy distribution of an AGN (coloured curves) compared to a starburst galaxy (grey curve). Different physical processes around the supermassive black hole contribute distinct spectral components that cannot be reproduced by stellar populations alone. Figure created with AGNFITTER-RXmartinez-ramirez2024, courtesy of L. Martínez-Ramírez.
• Figure 5: Multi-frequency radio observations of Cygnus A perley1984, showing the classic double-lobed structure with jets extending over 100 kpc from the central black hole. This is one of the brightest radio sources in the sky and the first identified extragalactic jet baade1954. Cygnus A has recently been studied also by JWST ogle2025. Image credits: https://www.nrao.edu/archives/items/show/33386.