National Astronomical Observatory of Japan

Cosmological Constraints from the First-Year of the Subaru Hyper Suprime-Cam Survey

| Science

The 3-dimensional dark matter map of the Universe. Moving from top to bottom, the observed areas are located farther and farther away, thus show us earlier and earlier epochs of the Universe. The density distribution of the dark matter has evolved with time. In this study, the growth of the fluctuations is measured precisely.

Using the powerful Japanese Subaru Telescope, the Hyper Suprime-Cam (HSC) survey collaboration team has made and analyzed the deepest wide-field map of the three-dimensional distribution of matter in the Universe. This was done by making precise measurements of the lumpiness of matter in the Universe, which constrains the properties of the “dark energy” that dominates the energy density of the Universe.

Although dark matter cannot be seen directly, its gravitational effects, predicted by Albert Einstein’s theory of general relativity, cause stretching and squeezing of the light from distant galaxies as the light travels across the cosmos. These effects can be detected by the Subaru Telescope. They are witness to the growth of cosmic structure and can be used to unlock the mysteries of dark energy. The simplest model for dark energy was introduced by Einstein, termed the “Cosmological Constant.” This model can explain all existing observations, including those of HSC.

With the high-precision HSC data, the team measured the lumpiness. The result is consistent with the value obtained by other studies, which surveyed brighter and thus nearer-by galaxies than did the HSC; the consistency of results at different distances and thus cosmic epochs gives confidence in the robustness of the results.

On the other hand, it has a slightly smaller value for the fluctuations than predicted by the simplest cosmological model. This could be just a statistical fluctuation due to the limited amount of data available, or it might be a sign of the breakdown of the standard model of the Universe, based on General Relativity and the cosmological constant.

The HSC survey is on-going and the new HSC results come from a mere one tenth of the final survey. Upon completion, the survey will put considerably tighter constraints on cosmological parameters, deepening and further testing our understanding of both dark matter and dark energy.

The research paper has now been submitted to the Publications of the Astronomical Society of Japan and will undergo rigorous peer review from the scientific community. (Cosmology from cosmic shear power spectra with Subaru Hyper Suprime-Cam first-year data)

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