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ING science news release
6th April, 2022

New Detection Method for Quasars in the Early Universe

Astronomers from The Netherlands, UK and Germany have developed a new method to find distant quasars (quasi-stellar objects) which better distinguishes them from other objects that look like them. Using machine learning techniques and spectroscopic data taken with the Isaac Newton Telescope (INT), the researchers discovered possibly the highest-redshift quasar ever observed with the INT.

A quasar is an extremely bright active centre of a galaxy, powered by a supermassive black hole that can be up to a billion times heavier than the Sun. Some supermassive black holes in the centres of galaxies are inactive, like the black hole at the centre of the Milky Way, but many are active, surrounded by a swirling disc of superheated gas. The black holes launch jets that reach hundreds of thousands of light-years into intergalactic space. They accelerate charged particles at speeds close to the speed of light, making them among the most powerful particle accelerators in the universe. Gas ejection by jets is essential for regulating mass and star formation in some of the most massive galaxies. Consequently, supermassive black holes play an important role in the formation and evolution of galaxies.

Quasars are therefore ideal objects for studying the evolution of the universe, especially in its earliest stages. One of the biggest challenges facing astronomers is finding these objects. Because they are so far away, quasars are seen as faint red dots in the sky.

Ironically, from Earth these powerhouses at the 'edge' of the universe look very similar to objects like red dwarfs. Red dwarf stars are much smaller than our Sun, and astronomers can only observe them within a few hundred light years. Because there are so many more red dwarf stars than quasars, most samples of promising quasar candidates have traditionally been heavily contaminated with such dwarf stars.

The astronomers implemented the new method on a catalogue of sources from the wide-field sky survey of Pan-STARRS, a set of optical imaging survey telescopes in Hawaii. This was supported by a catalogue of radio sources from LOFAR, ASTRON's low-frequency radio telescope in the Netherlands. Using the combined data, they identified sources that are most likely quasars. To properly identify these objects, they measured the spectra of a small number of candidates with the INT.

This study confirmed that one of the candidates is indeed a very bright quasar, from the time the Universe was less than a billion years old. The discovery of this never-before-seen quasar shows that this technique opens up new ways to discover more quasars in the early Universe, both in existing and future surveys. The researchers expect that hundreds of other quasars could be hidden, as the newly discovered quasar was found in a search of a relatively small area of the sky.

A spectrum of P144+50 taken with the IDS spectrograph on the INT. The characteristic break blueward of the Lyman-alpha spectroscopic line is clearly visible, and unambiguously identifies this object as a high-redshift quasar, with a redshift of z = 5.66 based on its Lyman-alpha emission. The orange line indicates the noise level of the spectrum. Large format: PNG.

Jonah Wagenveld, the lead author of this research, said: "Observing with the INT is one of the most unique experiences I have had as an early-career astronomer. It is impressive to see first-hand the science that can still be done using it."

Aayush Saxena, one of the co-authors, added: "Using machine learning-based methods to select very high redshift quasars is very timely in the era of big-data astronomy, which will be spearheaded by future facilities such as Euclid and the Vera Rubin Observatory. We were very excited to have discovered this previously unknown quasar, which is probably one of the most distant objects ever discovered by the venerable INT."

About the Isaac Newton Telescope

Based on observations made with the Isaac Newton Telescope (INT) operated on the island of La Palma by the Isaac Newton Group of Telescopes (ING) in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias (IAC). The ING is funded by the Science and Technology Facilities Council (STFC-UKRI) of the United Kingdom, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) of the Netherlands, and the IAC in Spain. IAC's contribution to ING is funded by the Spanish Ministry of Science, Innovation and Universities.

Journal article

J. D. Wagenveld, A. Saxena, K. J. Duncan, H. J. A. Röttgering, M. Zhang, 2022, "Revealing new high redshift quasar populations through Gaussian mixture model selection", A&A, 660, A22. Paper: NASA ADS | DOI.

More information

"New detection method for quasars in the early Universe", NOVA press release, 9th February 2022.


Jonah Wagenveld (Max-Planck Institut fur Radioastronomie, Germany)

Javier Méndez (ING PR Officer)

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Last modified: 29 November 2022