ALMA moment-0 map of the CO J = 4–3 line of the new source. Credit: Monthly Notices of the Royal Astronomical Society (2025). DOI: 10.1093/mnras/staf1655
An international team of astronomers used Atacama’s Large Millimeter/submillimeter Array (ALMA) to observe a well-known quasar known as Cloverleaf. As part of their observations, they accidentally discovered a new ultra-luminous infrared galaxy. The discovery was reported on September 30 in the Monthly Notices of the Royal Astronomical Society.
With infrared luminosities of over a trillion solar luminosities and star formation rates of between 100 and 1,000 solar masses per year, ultraluminous infrared galaxies (ULIRGs) are the most intense star-forming galaxies in the local universe. Therefore, the discovery of new galaxies of this type could be important for improving the understanding of star formation and evolution.
H1413+117, nicknamed Cloverfield, is a four-lensed quasar with a redshift of about 2.56. Recently, a group of astronomers led by Natsuki H. Hayatsu studied the Cloverfield with ALMA. Surprisingly, these observations revealed the presence of a ULIRG lurking behind the quasar.
“Dusty submillimeter-selected galaxies, without optical counterparts, contribute to a non-negligible fraction of star formation in the early universe. However, such a population is difficult to detect by classical studies based on optics and ultraviolet. We report the chance discovery of such an optically dim galaxy, behind the four-lensed quasar z = 2.56, H1413+117,” the report said. explain the researchers.
The new ULIRG was identified about 6 arcseconds from the Cloverfield quasar, with a redshift of about 3.39. The galaxy has a molecular mass of between 40 and 230 billion solar masses, and the mass of its black hole has been estimated at around 0.1 billion solar masses.
The total X-ray luminosity of the new ULIRG was measured at around 400 tredecillion erg/s, while its total infrared luminosity was found to be at a level of 2.8 trillion solar luminosities. The system is optically dark and appears very obscured.
The study found that the molecular gas in this ULIRG has not yet dynamically stabilized, likely due to a merger of major gas-rich galaxies in its early stages. Therefore, astronomers predict that the galaxy is likely destined to continue as stars, with its rich molecular budget, triggered by the merger process.
The researchers added that it is possible that the studied ULIRG is in the progenitor stage of the hot dust obscured galaxy (DOG) phase, perhaps evolving into the active naked galaxy cores (AGN) phase and then into the elliptical galaxy in the local universe. However, more in-depth studies, focusing on the molecular gas of the galaxy, are necessary in order to draw definitive conclusions on the current evolutionary state of this system.
“To infer the evolutionary stage of such an optically dark galaxy, whether it is a massive starburst, a QSO (quasi-stellar object) or a hot DOG, it is essential to clarify the physical state of the gas, particularly the dense molecular gas that provides the fuel for star formation, and this will be the subject of future follow-up studies,” the paper’s authors conclude.
Written for you by our author Tomasz Nowakowski, edited by Stephanie Baum, and fact-checked and revised by Robert Egan, this article is the result of painstaking human work. We rely on readers like you to keep independent science journalism alive. If this reporting interests you, consider making a donation (especially monthly). You will get a without advertising account as a thank you.
More information:
Natsuki H. Hayatsu et al., Chance discovery of an ultra-luminous optically dark infrared galaxy at z = 3.4, Monthly Notices of the Royal Astronomical Society (2025). DOI: 10.1093/mnras/staf1655. On arXiv: DOI: 10.48550/arxiv.2510.00590
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