December 17, 2008
A research group led by graduate student Violette Impellizzeri from the Max Planck Institute for Radio Astronomy used the 328 foot (100m) Effelsberg radio telescope to detect water at the greatest distance from Earth so far. The water vapor was discovered in the quasar MG J0414+0534 at redshift 2.64, which corresponds to light travel time of 11.1 billion years, a time when the universe was only a fifth of the age it is today. The water vapor is thought to exist in clouds of dust and gas that feed the super-massive black hole at the center of the distant quasar. The detection was later confirmed by high-resolution interferometric observations with the Expanded Very Large Array (EVLA).
This discovery of water in the early universe was possible due to the chance alignment of a foreground galaxy and the distant quasar MG J0414+0534. The foreground galaxy acts like a cosmic telescope, magnifying and distorting the light from the quasar, and forms four distinct images of the quasar. Without this gravitational-lensing effect, 580 days of continuous observations with the 328 foot (100m) telescope would have been needed instead of the 14 hours used to make this remarkable discovery.
The Effelsberg radio telescope also detected water from MG J0414+0534. The object is within the right redshift interval to stretch the line emission of the water molecule from its original frequency of 22 GHz to 6 GHz and so within the tuning range of the 6 GHz receiver installed at the telescope.
"It is interesting that we found water in the first gravitationally magnified object we observed from the distant universe", said co-author John McKean. "This suggests that water may be much more abundant in the early universe than first thought, and it can be used for further research into super-massive black holes and galaxy evolution at high redshift."
The water emission was seen in the form of a maser, which is beamed radiation similar to a laser, but at microwaves. The signal corresponds to a luminosity of 10,000 times the luminosity of the Sun. Such astrophysical masers are known to originate in regions of hot and dense dust and gas. With the detection of water from MG J0414+0534, it is the first time such a dense gas cloud has been observed in the early universe, and it shows that the conditions for the water molecule to form and survive already existed only 2.5 billion years after the Big Bang.
Water masers have been found in a number of galaxies at closer distances. Typically, they are thought to arise in the hot gas and dust closely orbiting a super-massive black hole at the galaxy's core. This amplified radio emission is more often observed when the orbiting disk is seen nearly edge-on. However, the astronomers say MG J0414+0534 is oriented with the disk almost face-on as seen from Earth. "This may mean that the water molecules in the masers we're seeing are not in the disk, but in the super-fast jets of material being ejected by the gravitational power of the black hole," said John McKean.
For the future, the detection of water in distant galaxies may still be challenging due to the sensitivity limitations of current-day telescopes. Of the nearby galaxies within half a billion light-years from Earth, only about one hundred galaxies show detectable water vapor emission, and almost all of them are relatively nearby. "In 2003, I was already participating in the detection of water mega-maser emission in the galaxy 3C 403," said Christian Henkel, co-author of the study. At that time, it was the most distant galaxy where water had been detected. Later on, this record went to a galaxy with water emission at redshift 0.66, (light travel time of 6 billion years). "Now MG J0414+0534 at redshift 2.64 is by far the most distant galaxy to show water vapor emission," he said.
"Because water masers arise close from the cores of galaxies, our result opens new interesting possibilities for studying super-massive black holes at a time when galaxies were forming," said Violette Impellizzeri. "It will also generate further searches for water in other distant galaxies with the telescopes we have at our disposal today and with the next generation of radio telescopes; we now know water is out there."