"There are hundreds of lens galaxies that we know about, but almost all of them are relatively nearby, in cosmic terms," said Wong, first author on the team's science paper, which was published in the July 10 issue of The Astrophysical Journal Letters. "To find a lens as far away as this one is a very special discovery because we can learn about the dark-matter content of galaxies in the distant past. By comparing our analysis of this lens galaxy to the more nearby lenses, we can start to understand how that dark-matter content has evolved over time."
Tran and her team were studying star formation in two distant galaxy clusters, including IRC 0218, when they stumbled upon the gravitational lens. In poring over the spectrographic data from Keck, Tran spotted a strong detection of hot hydrogen gas -- a clear signature of star birth -- that appeared to arise from a massive, bright elliptical galaxy. Previous observations had showed that the giant elliptical was an old, sedate galaxy that had stopped making stars a long time ago.
Another puzzling discovery was that the young stars were at a much farther distance than the massive elliptical.
"I was very surprised and very worried," Tran recalled. "I thought we had made a major mistake with our observations."
The astronomer soon realized she hadn't made a mistake when she looked at the Hubble images taken in blue wavelengths, which revealed the glow of fledgling stars. The images, taken by the Advanced Camera for Surveys and the Wide Field Camera 3, revealed a blue, eyebrow-shaped object next to a smeared blue dot around the big elliptical. Tran recognized the unusual features as the distorted, magnified images of a more distant galaxy behind the elliptical, the signature of a gravitational lens.
Another puzzling discovery was that the young stars were at a much farther distance than the massive elliptical.
"I was very surprised and very worried," Tran recalled. "I thought we had made a major mistake with our observations."
The astronomer soon realized she hadn't made a mistake when she looked at the Hubble images taken in blue wavelengths, which revealed the glow of fledgling stars. The images, taken by the Advanced Camera for Surveys and the Wide Field Camera 3, revealed a blue, eyebrow-shaped object next to a smeared blue dot around the big elliptical. Tran recognized the unusual features as the distorted, magnified images of a more distant galaxy behind the elliptical, the signature of a gravitational lens.
