Most distant galaxy yet is identified

Posted by Emma Woollacott

Scientists have discovered the most distant - and oldest - galaxy yet, viewing it just 600 million years after the Big Bang.

ESO previously reported a more distant object, but further work failed to find anything, and most astronomers now believe it's not a valid result.        

"Using the ESO Very Large Telescope we have confirmed that a galaxy spotted earlier using Hubble is the most remote object identified so far in the universe," says Matt Lehnert  of the Observatoire de Paris.

"The power of the VLT and its SINFONI spectrograph allows us to actually measure the distance to this very faint galaxy and we find that we are seeing it when the Universe was less than 600 million years old."

These first galaxies are hard to spot. By the time that their light gets to Earth they appear very faint and small, with the light falling mostly in the infrared part of the spectrum because it's  been redshifted by the expansion of the universe. Making it even harder, at this period the universe was largely filled with a hydrogen fog.

But the new Wide Field Camera 3 on the NASA/ESA Hubble Space Telescope discovered several candidate early galaxies in 2009. Lehnert's team observed one of these, UDFy-38135539, for 16 hours, and found that they'd clearly detected the glow from hydrogen at a redshift of 8.6, making this galaxy the most distant object ever confirmed by spectroscopy.

One of the more surprising observations is that the glow from UDFy-38135539 seems not to be strong enough on its own to clear the hydrogen fog.

"There must be other galaxies, probably fainter and less massive nearby companions of UDFy-38135539, which also helped make the space around the galaxy transparent," says Mark Swinbank of Durham University.

"Without this additional help the light from the galaxy, no matter how brilliant, would have been trapped in the surrounding hydrogen fog and we would not have been able to detect it."