Webb captures a stunning quasar-galaxy merger in the distant universe

An international research group led by the Italian National Institute for Astrophysics (INAF) and composed of 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 a quasar. within the PJ308–21 system and two massive satellite galaxies in the distant universe.

The observations, made in September 2022, revealed unprecedented and stunning detail, providing new insights into the growth of galaxies in the early universe. The results, presented on July 5 during the meeting of the European Astronomical Society (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 studied with NIRSpec when the universe was less than a billion years old (redshift z = 6.2342) , have discovered data of sensational quality: the instrument “captured” the spectrum of the quasar with an uncertainty of less than 1% per pixel.

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

The discovery has enabled 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 the quasar and the surrounding galaxies are highly developed in mass and metal enrichment and continuously growing.

This has profound implications for our understanding of the cosmic history and 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 rapid accretion. already turbulent in the first billion years of cosmic history, aided by the rich galactic environment in which these sources form.”

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

The observations were carried out in integral field spectroscopy mode: 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 by the expansion of the universe. This allows the study of different gas tracers (emission lines) using a 3D approach.

Thanks to this technique, the INAF-led team discovered spatially extended emissions from various elements, which were used to study the properties of the ionizing interstellar medium, including the source and strength of the photoionizing radiation field, metallicity, dust obscuration, density of electrons and the temperature and rate of star formation.

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

Federica Loiacono, astrophysicist, researcher and postdoctoral fellow working at INAF, says: “Thanks to NIRSpec, for the first time we can study in the PJ308-21 system the optical band, rich in valuable diagnostic data for the properties of near-black gas .the hole in the galaxy hosting the quasar and in the surrounding galaxies.

“We can, for example, look at the emission of hydrogen atoms and compare that to the chemical elements produced by stars to determine how metal-rich the gas in galaxies is.

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

She adds, “Thanks to the near- and mid-infrared sensitivity of the James Webb Space Telescope, it was possible to study the spectrum of the quasar and its companion galaxies with unprecedented precision in the distant universe. Only the brilliant ‘view’ provided from JWST, with its unparalleled capabilities, can provide these observations.”

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

This transformative impact of the instruments aboard the James Webb Space Telescope underscores its crucial role in advancing astrophysical research.

“Until a couple of years ago, data on metal enrichment (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 its infancy”, concludes Decarli.