Subaru Telescope - 20 May 2010
A z=1.82 Analog of Local Ultra-massive Elliptical GalaxiesAn international team of astronomers led by Dr. Masato Onodera at the Commissariat a l'Energie Atomique in France has used the Subaru Telescope to take infrared spectra of a very distant, unusually bright, and massive elliptical galaxy. This galaxy is 10 billion light-years from Earth and was observed at a time when the Universe was only about one-quarter of its current age. Paradoxically, and in contrast with some previous studies, this galaxy appears to be similar to its cousins in the local Universe. Its size appears to be normal for its mass, and its velocity dispersion (about 300 km per second) is consistent with its large size. This research deepens the puzzle as to how and why some elliptical galaxies seem to reach their full size very early in the evolution of the Universe while other, very compact ones increase in volume a hundredfold over time.
Giant elliptical galaxies are the Universe’s most massive galaxies near to Earth. They have a regular, oval shape and lack the disk typical of spiral galaxies such as our own Milky Way. Using large telescopes, astronomers have identified elliptical galaxies over ten times more massive than the Milky Way and as far away from Earth as 10 billion light years. Observing the light from such distant elliptical galaxies permits the direct study of how they looked shortly after their formation and opens a window to exploring the past of the Universe.
Five years ago, extremely deep images from the Hubble Space Telescope (HST) suggested that distant elliptical galaxies may be twice to five times smaller than nearby, local elliptical galaxies of the same mass. If these findings were accurate, then the densities of the more distant elliptical galaxies are 10 to 100 times higher than that of the local ones. Since then, experts have debated how these very compact galaxies could expand over the intervening 10 billion years so that they matched the size of their local counterparts. Many questioned whether the measurements of the size of the distant elliptical galaxies were accurate. Could some measurement error or bias account for their apparently small size?
- Astrophysical Journal Letters (20 May 2010), vol.715, L6, doi: 10.1088/2041-8205/715/1/L6