National Astronomical Observatory of Japan

Deciphering Compact Galaxies in the Young Universe

| Science

A group of researchers using the Suprime-Cam instrument on the Subaru Telescope has discovered about 80 young galaxies that existed in the early universe about 1.2 billion years after the Big Bang. The team, with members from Ehime University, Nagoya University, Tohoku University, Space Telescope Science Institute (STScI) in the U.S., and California Institute of Technology, then made detailed analyses of imaging data of these galaxies taken by the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. At least 54 of the galaxies are spatially resolved in the ACS images. Among them, 8 galaxies show double-component structures and the remaining 46 seem to have elongated structures. Through a further investigations using a computer simulation, the group found that the observed elongated structures can be reproduced if two or more galaxies reside in close proximity to each other.

These results strongly suggest that 1.2 billion years after the Big Bang, galactic clumps in the young universe grow to become large galaxies through mergers, which then causes active star formation to take place. This research was conducted as part of the treasury program of Hubble Space Telescope (HST), "Cosmic Evolution Survey (COSMOS)". The powerful survey capability of the Subaru Telescope provided the essential database of the candidate objects in the early universe for this research project.

An example of galaxy that shows a double-component structure in the HST/ACS image.
An example of galaxy that shows a double-component structure in the HST/ACS image. North is up and east is left. Each panel has a size of 4" x 4", which corresponds to 85 kly x 85 kly at the distance of 12.6 billion light-years. The thumbnails of the HST/ACS I band (effective wavelength = 814 nm), the Subaru Telescope/Suprime-Cam NB711 and i'- and z'-bands are shown from left to right. Note that the NB711 image, which captures the Lyman-alpha line emitted by neutral hydrogen, shows spatially extended gas which is ionized by ultraviolet (UV) radiation from many massive stars. On the other hand, other band images prove the UV radiation from massive stars themselves. Original size (98KB)

For details, see Press Release: Deciphering Compact Galaxies in the Young Universe.