EPFL Scientists Enhance Precision in Measuring Quasar Host Galaxy Mass using Gravitational Lensing
March 15, 2024
Scientists from the Swiss Federal Institute of Technology in Lausanne (EPFL) have made a groundbreaking discovery that promises to revolutionize our understanding of early universe galaxy evolution and black hole formation. By utilizing the phenomenon of strong gravitational lensing, the researchers have achieved a precision in measuring quasar host galaxy mass that is three times superior to any existing technique.
The findings, recently published in the journal Nature Astronomy, provide deeper insights into the mass of galaxies hosting quasars, shedding light on galaxy formation models and black hole growth. The study’s senior author, EPFL astrophysicist Frédéric Courbin, emphasizes the significance of these precise measurements in the distant Universe, where conventional techniques lack precision and are subject to biases.
The technique of gravitational lensing allows scientists to compute the mass of a lensing object by observing the bending of light from background objects caused by massive objects in the foreground. Quasars, which are luminous manifestations of supermassive black holes, are notoriously challenging to measure due to their vast distances and overwhelming brightness. However, by combining gravitational lensing and quasars, Courbin realized over a decade ago that it was possible to measure the mass of a quasar’s host galaxy.
To identify suitable candidates for gravitational lensing quasars, Courbin and his colleagues turned to the Sloan Digital Sky Survey (SDSS) database. The team observed four candidates, three of which displayed lensing phenomena. Among the candidates, one stood out for its distinctive gravitational lensing rings: SDSS J0919+2720.
Careful analysis of the gravitationally lensed rings in SDSS J0919+2720 enabled the scientists to determine the mass of the two bright objects present. This task, however, would have been impossible without the recent development of a wavelet-based lens modeling technique by co-author Aymeric Galan, currently working at the Technical University of Münich (TUM).
Understanding the formation of supermassive black holes is one of the greatest challenges in astrophysics. Galan highlights that knowing the mass of a black hole and how it compares to its host galaxy allows scientists to validate or discard certain theories of formation. In the local Universe, the most massive galaxies typically host the most massive black holes, hinting at a connection between black hole growth and galaxy evolution. To test this theory, it is crucial to study these interactions both locally and in the distant Universe, as explained by lead author Martin Millon.
Gravitational lensing events are rare, with only one in a thousand galaxies exhibiting the phenomenon. The chances of finding a quasar acting as a gravitational lens are even more minuscule, at one in a million. However, the scientists anticipate that the upcoming ESA-NASA mission Euclid, scheduled for launch this summer, will detect hundreds of these lensing quasars, giving scientists further opportunities to explore the nature of early universe galaxy evolution and black hole formation.
The EPFL researchers’ groundbreaking work opens up a new avenue for obtaining precise and accurate mass estimates in the distant Universe. By pushing the limits of measurement techniques, scientists can unravel the mysteries of our cosmos and gain a deeper understanding of its origins.
Reference: Millon, M., Courbin, F., Galan, A., Sluse, D., Ding, X., Tewes, M., & Djorgovski, S.G. (2023). Strong gravitational lensing by AGNs as a probe of the quasar–host relations in the distant Universe. Nature Astronomy, 10.1038/s41550-023-01982-2