An international team of astronomers, including Leiden PhD student Elia Pizzati, has observed several ancient quasars that, surprisingly, appear to be floating alone in the early universe (less than a billion years after the Big Bang). Until now, astronomers, based on models, assumed that quasars are always found in crowded areas with many neighboring galaxies. The research has been published today in The Astrophysical Journal.
Quasars are among the brightest objects in the universe, formed when supermassive black holes at the centers of galaxies consume large amounts of gas. Although the presence of such supermassive black holes so early in the universe's history is astonishing, various models and simulations show that these bright quasars can indeed form in rare, densely populated regions of the young universe. The discovery of these solitary quasars challenges this assumption.
No Man's Land
In this study, led by Anna-Christina Eilers (MIT, USA), astronomers used the James Webb Space Telescope (JWST) to look back more than 13 billion years and study the cosmic surroundings of five known ancient quasars. They found a surprising variety in their environments. While some quasars reside in very dense areas with more than fifty neighboring galaxies as predicted by models, others appear to be floating in empty space with only a few stray galaxies nearby. The big question now is how such objects could form so early in the universe without a significant source of surrounding material to fuel their black holes.
'Some quasars seem to stand in a no man's land,' says lead author Anna-Christina Eilers. 'It's difficult to explain how these quasars could grow so large if they have nothing to feed on.' Further research will determine whether these quasars are truly so isolated or if they are surrounded by dust-enshrouded galaxies that are hidden from view.
Comparing with Models
Elia Pizzati and his colleagues at Leiden, Joseph Hennawi, Joop Schaye, and Matthieu Schaller, worked on interpreting the observations. Pizzati explains, 'To determine whether quasars can live in rare and densely populated environments or not, we need to know what these environments looked like at different cosmic times. In other words, we need to compare our observations of quasars and galaxies with our theoretical models of the spatial distribution of matter in the universe (the cosmic web).'
Such comparisons can be made with cosmological simulations that capture the evolution of this cosmic web throughout the universe's history. Not all simulations are suited for this task: to capture the rarest and densest environments where quasars are thought to live (according to theoretical models), simulations need to cover vast volumes (up to 10 billion light-years) and have sufficient numerical resolution to capture smaller structures where less massive galaxies are expected.
A New Simulation
For this study, a new simulation was used, developed at Leiden Observatory and the University of Durham: FLAMINGO-10k. This simulation contains over a trillion particles, making it one of the largest simulations ever.
Co-author Joseph Hennawi (Leiden Observatory) concludes: 'These results are important as they can teach us how supermassive black holes grew in the early universe and what the relationship is between the growth of supermassive black holes and the emergence of bright quasars. With the unprecedented capabilities of JWST, we can now study early quasars and galaxies in detail unimaginable before.'
Beloning voor hulp aan JWST
The observations are part of the EIGER-survey, a cycle 1 JWST GTO programme that targeted six quasar fields using the NIRCam instrument. GTO stands for Guaranteed Time Observations, which are observations allocated to reward scientists who contributed to the development of key hardware and software components or provided technical and interdisciplinary expertise for the JWST. The observations were carried out between August 2022 and June 2024. The FLAMINGO-10k simulation was performed at the end of 2023 on the COSMA machine in Durham and was intended as a follow-up N-body simulation that complements the existing simulations in the FLAMINGO suite.
This article appeared as a press release on astronomie.nl
Header image: This image, captured by the James Webb Space Telescope, shows a solitary, ancient quasar (circled in red) with fewer neighbouring galaxies (bright blobs) than expected. The observation challenges the prevailing, model-supported theory that quasars are always located in densely populated regions with many neighbouring galaxies. (c) Christina Eilers/EIGER team
Scientific article
EIGER VI. The Correlation Function, Host Halo Mass and Duty Cycle of Luminous Quasars at z ≳ 6. Door: Anna-Christina Eilers, Ruari Mackenzie, Elia Pizzati, Jorryt Matthee, Joseph F. Hennawi, Haowen Zhang, Rongmon Bordoloi, Daichi Kashino, Simon J. Lilly, Rohan P. Naidu, Robert A. Simcoe, Minghao Yue, Carlos S. Frenk, John C. Helly, Matthieu Schaller en Joop Schaye. Geaccepteerd voor publicatie in The Astrophysical Journal. https://doi.org/10.48550/arXiv.2403.07986
