An international team of astronomers has discovered a structure that is expected to develop into a galaxy supercluster or "protocluster" during the most active epoch of the Universe 10 billions years ago. This protocluster is forming stars at a high rate that cannot be easily accounted for by current models. Its fate will be to evolve into a complex system similar to the Virgo Supercluster, a massive structure in the local Universe of which our Galaxy is a member. The protocluster was first identified as one of the brightest sub-millimeter sources in the sky by the Planck satellite. Subsequent observations with ground and space-based telescopes have revealed its members and corroborated its protocluster designation. The Subaru Telescope played an important role in this study by identifying a concentration of young, massive galaxies actively forming stars in this protocluster region. Further studies of these bright sub-millimeter sources first identified by the Planck satellite, and subsequently revealed by the Herschel satellite, are in progress. The goal of this project is to better understand the assembly of massive structures such as protoclusters, the mechanisms driving their prodigious star formation rates, and the interplay between the dense environment and the rapid evolution of the galaxies that inhabit it.
Figure: Sky region showing the PHz G237 protocluster and the identified galaxy members. The left panel shows a multi-band image (11 arcmin x 11 arcmin) combining the Herschel sub-millimeter image at 350 micron in red (star formation tracer), the Spitzer image at 3.6 micron in green (stellar mass tracer), and the XMM-Newton X-ray image in blue (tracer of accreting supermassive black holes). The region observed with the Subaru Telescope is delimited by a yellow dashed rectangle. Galaxy members identified through observations with the Subaru Telescope are shown as yellow diamonds, and the galaxies identified spectroscopically are shown as light blue circles. The right panel shows a zoom in the central 2.7 arcmin x 1.9 arcmin region of the protocluster (red: 2.14 micron, green: 2.07 micron, blue: 1.25 micron). (Credit: ESA/Herschel and XMM-Newton; NASA/Spitzer; NAOJ/Subaru Telescope; Large Binocular Telescope; ESO/VISTA; Polletta et al. 2021; Koyama et al. 2021)
More details are available in the press release by the Large Binocular Telescope Observatory.
These results were published in Monthly Notices of the Royal Astronomical Society on March 1, 2021 (Koyama et al. "A Planck-selected dusty protocluster at z=2.16 associated with a strong over-density of massive Hα emitting galaxies,") and in Astronomy and Astrophysics on October 26, 2021 (Polletta et al. "Spectroscopic observations of PHz G237.01+42.50: a galaxy protocluster at z=2.16 in the Cosmos field").
The Subaru Telescope is a large optical-infrared telescope operated by the National Astronomical Observatory of Japan, National Institutes of Natural Sciences with the support of the MEXT Project to Promote Large Scientific Frontiers. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawai`i.
Guidelines for Use