Astronomers explore the properties of a dark hyperluminous quasar

Astronomers from the European University of Cyprus and the University of Hawaii have studied a recently discovered hyperluminous quasar known as COS-87259. Results of the study, published October 14 in the Monthly Notices of the Royal Astronomical Societyshed light on the properties of this quasar.

Quasars, or quasi-stellar objects (QSO), are active galactic nuclei (AGN) of very high luminosity, therefore cores of active galaxies, powered by supermassive black holes (SMBH), emitting electromagnetic radiation observable by radio, infrared, visible, ultraviolet. and X-ray wavelengths.

They are among the brightest and most distant objects in the known universe and serve as fundamental tools for many studies in astrophysics and cosmology.

Discovered at the end of 2022, COS-87259 is a hyperluminous quasar with a redshift of 6.85. The AGN is heavily obscured and has a bolometric luminosity of approximately 50 trillion solar luminosities. Such high brightness suggests that this object is powered by an SMBH with a mass of around 1.6 billion solar masses.

In total, the galaxy is estimated to have a stellar mass of around 170 billion solar masses and its star formation rate (SFR) has been calculated at a level of 1,300 solar masses per year.

In order to obtain more information about the properties of COS-87259, a team of astronomers led by Charalambia Varnava of the European University of Cyprus used its Bayesian Spectral Energy Distribution (SED) fitting code recently developed SMART (Spectral Energy Distributions Markov chain Analysis with Radiative Transfer Models).

“Our method allows us to explore the impact of four different AGN torus models and therefore to constrain the properties of the obscuring torus, but also to quantify the uncertainties on the AGN fraction, the mass of the black hole and the SFR of the galaxy adjusted,” the researchers explained.

The Varnava team found that the CYGNUS AGN torus model, with tapered disk geometry, provides the best fit to the COS-87259 SED. CYGNUS is the Cypriot model for galaxies and their NUclear Spectra collection of radiative transfer models.

This model predicts an AGN fraction for the galaxy greater than 85% and an SFR greater than 1,980 solar masses per year. Additionally, the predicted AGN bolometric luminosity was calculated at a level of 100 trillion solar luminosities, suggesting a black hole mass of approximately 3.2 billion solar masses. So, all of these values ​​are higher than previously thought.

According to the paper’s authors, the results imply that the torus of obscured quasars like COS-87259 has a large coverage factor and that these objects may be at least as numerous as unobscured quasars. They added that it would be very interesting to estimate the spatial density of such objects in larger fields with good infrared coverage, which will be studied by spacecraft like ESA’s Euclid or NASA’s Roman Space Telescope. .

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