Astronomers have found an exceptionally distant galaxy, ranked among the top 10 most distant objects currently known in space. Light from the recently detected galaxy left the object about 800 million years after the beginning of the universe, when the universe was in its infancy.The galaxy, designated LAEJ095950.99+021219.1, was first spotted in summer 2011. The find is a rare example of a galaxy from that early epoch, and will help astronomers make progress in understanding the process of galaxy formation.
This galaxy is extremely faint and was detected by the light emitted by ionized hydrogen. The object was first identified as a candidate early-universe galaxy using a unique technique that uses special narrow-band filters that allow a small wavelength range of light through.
A special filter fitted to the telescope camera was designed to catch light of narrow wavelength ranges, allowing the astronomers to conduct a very sensitive search in the infrared wavelength range.
"We have been using this technique since 1998 and pushing it to ever-greater distances and sensitivities in our search for the first galaxies at the edge of the universe," says Malhotra, an associate professor in the school. "Young galaxies must be observed at infrared wavelengths and this is not easy to do using ground-based telescopes, since the Earth's atmosphere itself glows and large detectors are hard to make."
To be able to detect these very distant objects which were forming near the beginning of the universe, astronomers look for sources which have very high redshifts. Astronomers refer to an object's distance by a number called its "redshift," which relates to how much its light has stretched to longer, redder wavelengths due to the expansion of the universe.
Objects with larger redshifts are farther away and are seen further back in time. LAEJ095950.99+021219.1 has a redshift of 7. Only a handful of galaxies have confirmed redshifts greater than 7, and none of the others is as faint as LAEJ095950.99+021219.1.
"We have used this search to find hundreds of objects at somewhat smaller distances. We have found several hundred galaxies at redshift 4.5, several at redshift 6.5, and now at redshift 7 we have found one," explains Rhoads. "We've pushed the experiment's design to a redshift of 7 – it's the most distant we can do with well-established, mature technology, and it's about the most distant where people have been finding objects successfully up to now."
"With this search, we've not only found one of the furthest galaxies known, but also the faintest confirmed at that distance," added Malhotra. "Up to now, the redshift 7 galaxies we know about are literally the top one percent of galaxies. What we're doing here is to start examining some of the fainter ones – thing that may better represent the other 99 percent."
Resolving the details of objects that are far away is challenging, which is why images of distant young galaxies such as this one appear small, faint, and blurry.
"As time goes by, these small blobs which are forming stars, they'll dance around each other, merge with each other and form bigger and bigger galaxies. Somewhere halfway through the age of the universe they start looking like the galaxies we see today – and not before. Why, how, when, where that happens is a fairly active area of research," explains Malhotra.
The image at the top of the page is a false color photo of the galaxy LAEJ095950.99+021219.1. In this image, blue corresponds to optical light (wavelength near 500 nm), red to near-infrared light (wavelength near 920 nm), and green to the narrow range of wavelengths admitted by the narrow bandpass filter (around 968 nm). LAEJ095950.99+021219.1 appears as the green source near the center of the image cutout.
The Daily Galaxy via Arizona State University
Image credit: James Rhoads
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