Using the Subaru Telescope and Gemini-North Telescope, a team of
astronomers has revealed that the supercluster CL1604, a distant
supercluster located about 7.3 billion light-years away, is a
large-scale 3-D structure extending over about 160 million light-years
in the north-south direction. This is more than two times more extended
than what was already known. Until now, we saw merely the “tip of the
iceberg” of the supercluster. The wide-field capability of the Subaru
Telescope enabled us to survey the whole of the supercluster and the
Gemini-North Telescope played a critical role in confirming the
structures. This is the outcome of the good synergy of the telescopes of
the Maunakea observatories.
Galaxies are distributed inhomogeneously in the Universe. It is
well-known that nearby galaxies are strongly influenced by their
environment, e.g., whether they are located in dense areas called galaxy
clusters or less dense areas called voids. However, how galaxies form
and evolve along with the growth of the cosmic web structures is one of
the hot topics of astronomy. A wide-field survey of the distant Universe
allows us to witness what actually happened with galaxies in the early
phase of structure formation in the Universe. Among the few
superclusters currently known, one of the best targets for study is the
supercluster CL1604. Based on previous studies, its extent is 80 million
light-years and its era is 7.3 billion years ago.
The uniqueness of the data taken by Hyper Suprime-Cam (HSC) on the
Subaru Telescope is the deep imaging data over a field wide enough to
fully cover the known supercluster and the surrounding area. A team led
by Masao Hayashi and Yusei Koyama from NAOJ estimated the distances of
individual galaxies from the galaxy colors using a technique called
“photometric redshift.” Then, the three dimensional picture of the
large-scale structures appears, which consists of several galaxy
clusters newly discovered in the north-south direction as well as the
structures already known (Figure 1).
Furthermore, the team used the Faint Object Camera and Spectrograph
(FOCAS) on the Subaru Telescope and the Gemini Multi-Object Spectrograph
(GMOS) on Gemini-North to confirm the precise distances of 137 galaxies
associated with the galaxy clusters revealed by HSC (Figure 2). It is
found that the supercluster is a complex large-scale structure not only
over the vast projected area but also along the line-of-sight direction
in 3D. The galaxies spread over the 160 million light-years seem to be
independent due to the vast area, however, the spectroscopic
observations tell us that the galaxies formed simultaneously and then
evolve along with the growth of large-scale structures.
Our Galaxy is a member of Local Group on the outskirts of Virgo
Galaxy Cluster. A team led by an astronomer from the University of
Hawaii recently revealed that the Virgo Cluster is a member of a more
extended enormous large-scale structure named the Laniakea Supercluster.
"The supercluster we discovered 7.3 billion years ago may grow to be a
huge large-scale structure similar to Laniakea where we live" said
Hayashi.
These results were published in Publications of the Astronomical Society of Japan (Hayashi et al., "The whole picture of the large-scale structure of the CL1604 supercluster at z∼0.9"). A preprint is available here.
Links
Source: Subaru Telescope
