researchers detect quasar host galaxies in the early universe
(Nanowerk News) New images from the James Webb Space Telescope have revealed, for the first time, the starlight from two massive galaxies housing actively growing black holes – quasars – visible less than a billion years after the Big Bang. A new study in Nature this week found the black hole has a mass close to a billion times that of the Sun, and the mass of its host galaxy is nearly a hundred times that, ratios similar to those found in the more recent universe. The powerful combination of the Subaru Telescope and JWST has opened new avenues for studying the distant universe.
The existence of massive black holes in the distant universe has raised more questions than answers for astrophysicists. How did this black hole get so big when the universe was so young? Even more puzzling, observations in the local universe show a clear connection between the masses of supermassive black holes and the much larger galaxies in which they are located. Galaxies and black holes are completely different sizes, so which came first: the black hole or the galaxy? It’s a “chicken-or-egg” problem on a cosmic scale.
An international research team, led by Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Project Researcher Xuheng Ding and Professor John Silverman, and Peking University Kavli Institute for Astronomy and Astrophysics (PKU-KIAA) Kavli Astrophysics Fellow Masafusa Onoue have began answering this question with the James Webb Space Telescope (JWST), launching in December 2021. Studying the relationship between parent galaxies and black holes in the early universe allows scientists to observe their formation, and see how they are related to each other. .
The study has been published in Natural (“Detection of starlight from a quasar host galaxy at a redshift above 6”).
Quasars are luminous, while their parent galaxies are dim, which makes it difficult for researchers to detect the dim galactic glow in quasar glare, especially at great distances. Before JWST, the Hubble Space Telescope was able to detect host galaxies from luminous quasars when the universe was under 3 billion years old, but not younger.
JWST’s extraordinary sensitivity and extremely sharp images at infrared wavelengths have finally allowed researchers to push this study back to the time when quasars and galaxies first formed. Just months after JWST began regular operations, the team observed two quasars, HSC J2236+0032 and HSC J2255+0251, at redshifts of 6.40 and 6.34 when the universe was about 860 million years old. Both of these quasars were discovered in the Subaru Telescope’s 8.2m depth survey program atop Maunakea in Hawaii. The relatively low luminosity of these quasars makes them a prime target for measurements of the properties of host galaxies, and the successful detection of these hosts represents the earliest epoch to date in which starlight has been detected in a quasar.
Images of the two quasars were taken at infrared wavelengths of 3.56 and 1.50 microns with JWST’s NIRCam instrument, and the host galaxy became clear after carefully modeling and reducing the glare from the accreting black hole. The asterisk of the host galaxy is also visible in the spectrum captured by NIRSPEC JWST for J2236+0032, further supporting the detection of the host galaxy.
Photometric analysis of the host galaxies found that both of these quasar host galaxies are very massive, measuring 130 and 34 billion times the mass of the sun, respectively. Measuring the velocity of the turbulent gas around the quasar from the NIRSPEC spectrum shows that the black hole driving it is also massive, measuring between 1.4 and 0.2 billion times the mass of the Sun. The ratio of the mass of the black hole to the mass of the host galaxy is similar to that of galaxies in the past, indicating that the connection between the black hole and its parent existed 860 million years after the Big Bang.
Ding, Silverman, Onoue and their colleagues will continue this study with larger samples using scheduled JWST Cycle 1 observations, which will further constrain the model for the coevolution of black holes and their host galaxies. The team recently learned that they have been granted additional time for JWST in their next cycle to study the host galaxy J2236+0032 in greater detail.
