STARLIGHT AND THE FIRST BLACK HOLES: RESEARCHERS DETECT THE HOST GALAXIES OF QUASARS IN THE EARLY UNIVERSE

STARLIGHT AND THE FIRST BLACK HOLES: RESEARCHERS DETECT THE HOST
GALAXIES OF QUASARS IN THE EARLY UNIVERSE

Maunakea, Hawaiʻi – An international team of scientists, including Chien-Hsiu Lee, staff
astronomer at W. M. Keck Observatory on Maunakea, Hawaiʻi Island, has captured images for
the first time of starlight from two massive galaxies hosting actively growing black holes, or
quasars, from less than a billion years after the Big Bang. The successful detection of these
hosts represents the universe’s earliest epoch to date at which light from stars has been
detected around a quasar.
These black holes have masses close to a billion times that of the Sun, and the ratio of the
black hole mass to host galaxy mass is similar to those seen in the more recent universe.
Initially discovered in a deep survey program of the Subaru Telescope on Maunakea, the two
quasars were then captured by the James Webb Space Telescope (JWST). This powerful
combination of ground-based observations from Subaru Telescope and space-based
observations from JWST has paved a new path to study the distant universe.
The study, 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, is published in today’s online issue of the journal Nature.
“This is the first time we’ve seen host galaxies from such an early age of the universe. It is only
possible thanks to JWST’s deep images, which enable us to model and subtract the light from
the quasar to reveal the host galaxy. We’ve seen quasars from this age previously, but they
were so bright it was impossible to subtract their light to reveal the host galaxy,” says Lee, coauthor of the study.

The zoomed-out image (left), the quasar image (center), and the host galaxy image after
subtracting the quasar light (right) (from left to right). The image scale in light years is indicated
in each panel. Credit: Ding, Onoue, Silverman, et al., JWST NIRCam 3.6 μm image of HSC
J2236+0032
Studying host galaxies and black holes in the early universe allows scientists to watch their
formation and see how they are related to one another. Quasars are luminous while their host
galaxies are faint, which has made it challenging for researchers to detect the dim light of the
galaxy in the glare of the quasar, especially at great distances. Before the JWST, the Hubble
Space Telescope was able to detect host galaxies of luminous quasars when the universe was
just under 3 billion years old, but no younger.
The superb sensitivity and ultra-sharp images of JWST at infrared wavelengths has finally
allowed researchers to push these studies to the time when quasars and galaxies first formed.
Just a few months after JWST started regular operations, the team observed two quasars, HSC
J2236+0032 and HSC J2255+0251, at redshifts 6.40 and 6.34 when the universe was
approximately 860 million years old, both of which were discovered using Subaru Telescope’s
deep survey program. The relatively low luminosities of these quasars made them prime targets
for measuring the properties of their host galaxies.
The 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 galaxies became apparent after carefully
modeling and subtracting glare from the accreting black holes. The stellar signature of the host
galaxy was also seen in a spectrum taken by JWST’s NIRSPEC for J2236+0032, further
supporting the detection of the host galaxy.
Photometric analyses found that these two quasar host galaxies are massive, measuring 130
and 34 billion times the mass of the Sun, respectively. Measuring the speed of the turbulent gas
in the vicinity of the quasars from the NIRSPEC spectra suggests the black holes that power
them are also massive, measuring 1.4 and 0.2 billion times the mass of the Sun. The ratio of the
black hole to host galaxy mass is similar to those of galaxies in the more recent past,
suggesting that the relationship between black holes and their hosts was already in place 860
million years after the Big Bang.

“I’m excited to see powerful ground-based and space-based telescopes working together to
tackle these challenges. Along with the Subaru Telescope, we will also be using Keck
Observatory’s MOSFIRE instrument to identify similar targets that JWST can observe and
enlarge the sample of ancient galaxies hosting quasars in the early universe,” says Lee.
The team of astronomers will continue this study using scheduled Cycle 1 JWST observations,
which will further inform models for the coevolution of black holes and their host galaxies.