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“Earliest galaxy” offers surprises

Nov. 4, 2013
Courtesy of University of Massachusetts Amherst
and World Science staff

As­tro­no­mers say they have iden­ti­fied the most dis­tant gal­axy ev­er de­tected, in a sur­vey not even de­signed to find one like it.

Be­cause light takes time to trav­el, the gal­axy is there­fore be­ing seen as it was ear­li­er in the his­to­ry of the uni­verse than any oth­er, they add.

Al­though oth­er Hub­ble-based ob­serva­t­ions have iden­ti­fied many oth­er can­di­dates for early-u­niverse ga­lax­ies, in­clud­ing some that may be even fur­ther, this one is the far­thest and ear­li­est whose dis­tance can be con­firmed with fol­low-up ob­serva­t­ions from the Keck I tel­e­scope, one of the larg­est on earth, the as­tron­o­mers said.

Univers­ity of Mas­sa­chu­setts Am­herst as­tron­o­mer Mau­ro Giav­a­lis­co and col­leagues iden­ti­fied the body as part of a ma­jor sur­vey of the early uni­verse con­ducted using NASA’s Hub­ble Space Tel­e­scope.

The sur­prise find­ing of a young gal­axy from a sur­vey that was not de­signed to find such bright early ga­lax­ies sug­gests that the in­fant uni­verse may har­bor a larg­er num­ber of in­tense star-forming ga­lax­ies than as­tron­o­mers be­lieved pos­si­ble, said the re­search­ers, re­port­ing their work in re­search jour­nal Na­ture

This means some the­o­ries may need re­vi­sion.

“We ex­pected to find a lot more small ob­jects with this sur­vey,” said Giav­a­lis­co. In the same way that throw­ing a brick through a win­dow should pro­duce a huge num­ber of small shards and very few large pieces, he adds, the­o­ry pre­dicts there should be many small ga­lax­ies “but just a few large ones. And our sur­vey was not really de­signed to find these early ga­lax­ies with such a high rate of star forma­t­ion. Howev­er, on the first try we see this very ac­tive ob­ject. So we’re not sure if we’re really, really lucky or if our pre­dic­tive mod­els are slightly of­f.”

The high lu­mi­nos­ity, pow­ered by star forma­t­ion ac­ti­vity, of this new gal­axy “raise a tan­ta­liz­ing ques­tion about wheth­er we’ve got the the­o­ry of gal­axy forma­t­ion cor­rect in its fun­da­men­tal ideas,” the as­tron­o­mer added.

The re­search­ers used two spe­cial cam­er­as on Hub­ble as part of the larg­est in­ves­ti­ga­t­ion of the dis­tant uni­verse ev­er made with the space tel­e­scope.

To iden­ti­fy the gal­axy from among myr­i­ads of oth­er, clos­er faint ga­lax­ies that ob­scure deep im­ages of the sky, they used a tech­nique called the “Lyman-break se­lec­tion” de­vel­oped by Giav­a­lis­co and oth­ers in the 1990s. It ex­ploits the ap­par­ent col­ors of ga­lax­ies as a crude dis­tance in­di­ca­tor. “Col­ors en­code a lot of phys­i­cal pro­cesses at work in them,” he points out, “such as wheth­er they form stars or not and how much dust is in them, be­cause dust dims stel­lar light and makes their col­ors red­der.”

But the tech­nique yields only crude dis­tance es­ti­mates, so as­tron­o­mers need to ac­cu­rately de­ter­mine the dis­tance to pre-selected re­mote ga­lax­ies. To do that, the sci­en­tists needed very sen­si­tive spec­tro­scop­ic, or light-analyzing tel­e­scopes to de­tect a spe­cif­ic fea­ture in the light emit­ted by hy­dro­gen known as the Lyman-alpha emis­sion line. The team used the Keck 10-meter tel­e­scope in Ha­waii, a very pow­er­ful spec­tro­scop­ic in­stru­ment. 

Re­sults yielded a “red­shift param­e­ter,” that is an in­di­ca­tor of dis­tance, of 7.51, by far the most dis­tant gal­axy ev­er recorded. At that time the uni­verse was an es­ti­mat­ed 700 mil­lion years old, com­pared to 13.8 bil­lion years to­day. The uni­verse is be­lieved to have been 8.5 times smaller than to­day, 600 times more dense and ex­pand­ing 8.5 times faster.

The as­tron­o­mers said the find­ings could yield new clues to an early pro­cess called re-ion­iz­a­tion. In it, a fog dropped away from the uni­verse and it went from be­ing dis­tri­bu­tion of cold, elect­rically neu­tral gas with no light sources, to be­ing vis­i­ble across large dis­tances.


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Astronomers say they have identified the most distant galaxy ever detected, in a survey not even designed to find such a thing. Because light takes time to travel, the galaxy is therefore being seen as it was earlier in the history of the universe than any other, they add. University of Massachusetts Amherst astronomer Mauro Giavalisco and colleagues identified the body as part of a major survey of the early universe conducted from the NASA’s Hubble Space Telescope. Although other Hubble-based observations have identified many other candidates for early-universe galaxies, including some that may be even further, this one is the farthest and earliest whose distance can be confirmed with follow-up observations from the Keck I telescope, one of the largest on earth, the astronomers said. The surprise finding of a young galaxy from a survey that was not designed to find such bright early galaxies suggests that the infant universe may harbor a larger number of intense star-forming galaxies than astronomers believed possible, said the researchers, reporting their work in research journal Nature. This means some theories may need revision. “We expected to find a lot more small objects with this survey,” said Giavalisco. In the same way physics predicts that throwing a brick through a window should produce a huge number of small shards and very few large pieces, he adds, theory predicts there should be many small galaxies “but just a few large ones. And our survey was not really designed to find these early galaxies with such a high rate of star formation. However, on the first try we see this very active object. So we’re not sure if we’re really, really lucky or if our predictive models are slightly off.” The high luminosity, powered by star formation activity, of this new galaxy “raise a tantalizing question about whether we’ve got the theory of galaxy formation correct in its fundamental ideas,” the astronomer added. “Predictions about the star formation rate distribution of galaxies are related to the physics of gas accretion onto galaxies and subsequent gas expulsion from them. These mechanisms are not yet fully understood.” The researchers used two special cameras on Hubble as part of the largest investigation of the distant universe ever made with the space telescope. To identify the galaxy from among myriads of other, closer faint galaxies that obscure deep images of the sky, they used a technique called the “Lyman-break selection” developed by Giavalisco and others in the 1990s. It exploits the apparent colors of galaxies as a crude distance indicator. “Colors encode a lot of physical processes at work in them,” he points out, “such as whether they form stars or not and how much dust is in them, because dust dims stellar light and makes their colors redder.” But the technique yields only crude distance estimates, so astronomers need to accurately determine the distance to pre-selected remote galaxies. To do that, the scientists needed very sensitive spectroscopic, or light-analyzing telescopes to detect a specific feature in the light emitted by hydrogen known as the Lyman-alpha emission line. The team used the Keck 10-meter telescope in Hawaii, a very powerful spectroscopic instrument. Results yielded a “redshift parameter,” that is an indicator of distance, of 7.51, by far the most distant galaxy ever recorded. At that time the universe was an estimated 700 million years old, compared to 13.8 billion years today. The universe is believed to have been 8.5 times smaller than today, 600 times more dense and expanding 8.5 times faster. The astronomers said the findings could yield new clues to an early process called re-ionization. In it, a fog dropped away from the universe and it went from being distribution of cold neutral gas with no light sources, to being visible across large distances.