Starship Asterisk*

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A research group led by Hiroshima University has revealed a picture of the increasing fraction of massive star-forming galaxies in the distant universe. Massive star-forming galaxies in the distant universe, about 5 billion years ago, trace large-scale structure in the universe. In the nearby universe, about 3 billion years ago, massive star-forming galaxies are not apparent. This change in the way star-forming galaxies trace the matter distribution is consistent with the picture of galaxy evolution established by other independent studies.

Galaxies in the universe trace patterns on very large scales; there are large empty regions (called “voids”) and dense regions where the galaxies exist. This distribution is called the cosmic web. The most massive concentrations of galaxies are clusters. The formation of the cosmic web is governed by the action of gravity on the invisible mysterious “dark matter” that exists throughout the universe. The normal baryonic material one can see falls into the dark matter halos and forms galaxies. The action of gravity over about the 14-billion-year history of the universe makes the halos cluster together. The location of galaxies or clusters in this enormous cosmic web tests our understanding of the way structure forms in the universe.

Increasingly, deeper and more extensive observations with telescopes like the 8-meter Subaru Telescope on Maunakea, Hawaii, provide a clearer picture of the way galaxies evolve within the cosmic web. Of course, one cannot see the dark matter directly. However, one can use the galaxies that are seen to trace the dark matter. It is also possible to use the way the gravity of clusters of galaxies distort more distant background galaxies, weak gravitational lensing, as another tracer.

The Hiroshima group combined these two tracers: galaxies and their weak lensing signal to map the changing role of massive star-forming galaxies as the universe evolves. ...

• Astrophysical Journal 833(2):156 (2016 Dec 20) DOI: 10.3847/1538-4357/833/2/156
  arXiv.org > astro-ph > arXiv:1606.07439 > 23 Jun 2016 (v1), 18 Oct 2016 (v2)