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Journal Club: Record-breaking galaxy offers insight into early universe

A color image of the newly found, most distant galaxy. From the Hubble Space Telescope and Spitzer telescopes. Image credit:  I. Labbé (Leiden University), NASA/ESA/JPL-Caltech

A color image of the newly found, most distant galaxy. From the Hubble Space Telescope and Spitzer telescopes.
Image credit: I. Labbé (Leiden University), NASA/ESA/JPL-Caltech

A new champion has been crowned in the hunt for the most distant, independently-confirmed galaxy ever observed. Called EGS8p7, the galaxy existed when the universe was a mere 570 million years old, beating the previous frontrunner by almost 100 million years. Its discovery, reported in the August 28 issue of Astrophysical Journal Letters, could give astronomers insight into the formation of the first stars and galaxies in the universe.

Astronomers often spot nearby galaxies using a signature radiation called Lyman alpha emission, produced when newborn stars heat the neutral hydrogen immediately around them. But hydrogen can both emit and absorb Lyman alpha. So the overwhelming amount of hydrogen gas that was around during a mysterious, galaxy and star-forming epoch known as reionization – which started roughly 500 million years after the Big Bang and lasted for another 500 million – absorbed nearly all the Lyman alpha emission from young galaxies, obscuring most objects from this era.

“We didn’t think we’d see Lyman alpha at these crazy distances, but we figured it’s worth a shot,” says astronomer Adi Zitrin of Caltech in Pasadena, California, lead author on the paper.

Because the universe constantly expands, light waves traveling within it get stretched. This process, known as redshifting, causes light from very distant objects to be lengthened toward longer and redder wavelengths. In order to identify EGS8p7, the team combed through Hubble Space Telescope images for extremely red galaxies, indicating that their light had been stretched completely into the infrared portion of the electromagnetic spectrum.

While suggestive of their great distance, the technique only offers an estimate of how old and far away these objects are. In order to independently confirm their findings, the team then turned to the 10-meter ground-based Keck telescopes on Mauna Kea in Hawaii, which stared at EGS8p7 continuously over two nights. This provided enough light from the galaxy to see its faint Lyman alpha emission. By calculating how much the radiation had been redshifted over time, the team was able to confirm the object’s record-breaking distance.

One reason we see this particular galaxy could be that it produced so much ultraviolet radiation during its lifetime as to burn away most of the neutral hydrogen gas in its surroundings. EGS8p7 might also be telling us something interesting about reionization—that it progressed at slightly different rates in different parts in the universe. “While one single detection is not changing our whole picture of course, this [galaxy] may indicate that the reionization process is indeed quite patchy,” says astronomer Pascal Oesch of Yale University in New Haven, Connecticut, another member of the team.

The discovery is “a nice step, because pushing the frontier is always the fun part of astronomy,” says Garth Illingworth, an astronomer at the University of California, Santa Cruz who was not involved in the work. He added that confirming more distant galaxies may prove challenging, because even a slight drop in brightness will make them hard to see with ground-based telescopes. It could take until the launch of the powerful James Webb Space Telescope in 2018 before this current record is broken.

But Zitrin doesn’t rule out the possibility, saying the finding “might open the door” to other objects at this distance. Astronomers hadn’t even been expecting to see Lyman alpha emissions in this galaxy. Now that they know they can, he doesn’t think cosmologists will “have to wait too long until the next one comes along.”

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