National Astronomical Observatory of Japan

Mapping Galaxy Formation in Dual Mode

| Science

A team of astronomers led by David Sobral (Leiden Observatory and Royal Observatory of Edinburgh) has explored the synergies between the Subaru Telescope and the United Kingdom Infra-Red Telescope (UKIRT) to locate numerous distant galaxies in the ancient universe and investigate their star formation activity. By combining narrow-band filter observations from both the Subaru Telescope and the UKIRT, the team has been able to obtain clean panoramic maps of parts of the distant universe about 9 billion years ago. This dual mode of surveying faint galaxies provides a powerful technique for selecting and studying star-forming galaxies during their formation and evolution.

Figure 1: An example of how the dual narrow-band technique works. UKIRT images (top) are obtained with a narrow- (left) and a broad-band (middle) filter, and, after subtraction, a galaxy with an emission line (right) is identified. Subaru images (bottom) are obtained with different narrow- and broad-band filters, and the same procedure is followed. Galaxies with emission lines in both data sets are automatically confirmed to be galaxies forming stars at a distance of about 9 billion light years away.
Figure 2: Star formation history of the Universe. This shows that star formation activity in the Universe as a whole has been declining over the last 11 billion years. The dual line technique can provide a reliable estimate of star formation activity 9 billion years ago. It allows this estimate by using the two emission lines for the first time; each emission line is shown separately and reveals good agreement about star formation during the same era.