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“Population Census” of Galaxies Buried in Dust

| Science

A research team led by Bunyo Hatsukade, a postdoc researcher, and Kouji Ohta, a professor, both from the Graduate School of Science, Kyoto University, revealed that approximately 80% of the unidentifiable millimeter wave signals from the universe is actually emitted from galaxies, based on the observations with ALMA (Atacama Large Millimeter/submillimeter Array). ALMA’s high resolving power and sensitivity enables us to pinpoint the locations of those galaxies rich in fine solid particles (dust).

With the ALMA telescope, the research team observed the “Subaru/XMM-Newton Deep Survey Field” in the direction of the constellation Cetus, and succeeded in identifying 15 extremely faint galaxies which had been previously unknown. In addition, they also successfully measured the number density of galaxies with 10 times less luminosity than ones previously observed with the conventional millimeter instruments. Their densities well match the prediction by theories of galaxy formation. Therefore, the researchers consider that they managed to capture more like “normal” galaxies, which had been impossible to detect up to now, than extremely bright “submillimeter-luminous galaxies”. Using ALMA and the Subaru Telescope, the research team is now seeking to uncover the overall picture of galaxy formation and evolution while conducting observations of much darker galaxies.

Artist’s illustration of the observed field.
Artist’s illustration of the observed field. In each close-up view, left is the illustration of the optical (blue) and conventional millimeter/submillimeter (red) image and right is the optical and ALMA image.
Existing millimeter/submillimeter telescopes could not identify the sources of the emission due to their low resolution, however, ALMA pinpoints the galaxies which emit the emission. These objects were not detected in the optical observations, which indicate that they are heavily embedded in dust.

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