Webb captures a stunning merger of quasars and galaxies in the distant universe

An international research group led by the Italian National Institute of Astrophysics (INAF) and involving 34 research institutes and universities worldwide used the Near-Infrared Spectrograph (NIRSpec) on board the James Webb Space Telescope (JWST) to witness the dramatic interaction between the quasar. inside the PJ308–21 system and two massive satellite galaxies in the distant universe.

Observations made in September 2022 revealed unprecedented and awe-inspiring details that provide new insight into the growth of galaxies in the early universe. The results, presented on July 5 during the European Astronomical Society meeting (EAS 2024) in Padua (Italy), will soon be published in Astronomy and astrophysics.

Observations of this quasar (already described by the same authors in another study published last May), one of the first to be studied with NIRSpec when the universe was less than a billion years old (redshift z = 6.2342), revealed data of sensational quality: the instrument “captured ” spectrum of a quasar with an uncertainty of less than 1% per pixel.

The host galaxy PJ308–21 shows high metallicity and photoionization conditions typical of an active galactic nucleus (AGN), while one of the satellite galaxies shows low metallicity (which refers to the abundance of chemical elements heavier than hydrogen and helium) and induced photoionization. by star formation; a higher metallicity characterizes the second satellite galaxy, which is partially photoionized by the quasar.

This discovery allowed astronomers to determine the mass of the supermassive black hole at the center of the system (about 2 billion solar masses). It also confirmed that both the quasar and the surrounding galaxies are highly evolved in mass and metal enrichment and in constant growth.

This has profound implications for our understanding of cosmic history and the chemical evolution of galaxies, highlighting the transformative impact of this research.

Roberto Decarli, a researcher at INAF in Bologna and first author of the paper, explains: “Our study reveals that both the black holes at the center of high-redshift quasars and the galaxies that host them undergo extremely efficient and turbulent growth already in the first billion years cosmic history, aided by the rich galactic environment in which these sources arise.”

The data were acquired in September 2022 as part of Program 1554, one of the nine Italian projects of the first observing cycle of the JWST. Decarli leads this program to observe a merger between a quasar host galaxy (PJ308-21) and two of its satellite galaxies.

The observations were carried out in the mode of integral field spectroscopy: for each image pixel, the spectrum of the entire optical band (in the rest frame of the source) can be observed, shifted towards the infrared region by the expansion of the universe. This allows the study of different gas tracers (emission lines) using a 3D approach.

With this technique, the INAF-led team detected spatially extended emissions from a variety of elements that were used to study the properties of the ionized interstellar medium, including the source and hardness of the photoionizing radiation field, metallicity, dust obscuration, electron density, and the temperature and rate of star formation.

In addition, the researchers marginally detected emission of starlight associated with companion sources.

Federica Loiacono, astrophysicist, researcher and postdoc working at INAF, says: “Thanks to NIRSpec, we can study for the first time in the PJ308-21 system an optical band, rich in valuable diagnostic data on the properties of the near-black gas. holes in the quasar host galaxy and in nearby galaxies.

“For example, we can see the emission of hydrogen atoms and compare it to the chemical elements produced by stars to see how metal-rich the gas in galaxies is.

“The experience of reducing and calibrating this data, one of the first collected with NIRSpec in integral field spectroscopy mode, has provided the Italian community with a strategic advantage in managing similar data from other programs.” Loiacono is the Italian contact person for NIRSpec data reduction in the INAF JWST Support Center.

He adds: “The sensitivity of the James Webb Space Telescope in the near- and mid-infrared has made it possible to study the spectrum of quasars and companion galaxies with unprecedented precision in the distant universe. Only the excellent ‘view’ offered by JWST with its unique capabilities can make these observations possible.”

The work was a real “emotional roller coaster,” Decarli continues, “with the need to develop innovative solutions to overcome the initial difficulties of data reduction.”

This transformative impact of the James Webb Space Telescope’s onboard instruments underscores its essential role in advancing astrophysical research.

“Until a few years ago, metal enrichment data (essential for understanding the chemical evolution of galaxies) were almost beyond our reach, especially at these distances. Now we can map them in detail with just a few hours of observation, even in galaxies observed when the universe was in diapers,” concludes Decarli.