Hubble Detects Faintest-Ever Early Universe Galaxies
January 8, 2014

AAS 2014: Hubble Used To Locate Faintest-Ever Early Universe Galaxies

redOrbit Staff & Wire Reports - Your Universe Online

Using the Hubble Space Telescope, a team of researchers has discovered the smallest, faintest and most numerous galaxies ever discovered in the remote universe, according to research presented Tuesday at the annual meeting of the American Astronomical Society (AAS) in Washington DC.

The University of California, Riverside-led team – whose research will also appear in the January 10 issue of The Astrophysical Journal – used Hubble to confirm the long-suspected underlying population of galaxies, which produced the majority of new stars during the universe’s early days.

Hubble photographed the 58 young, diminutive galaxies as they appeared over 10 billion years ago, the university explained in a statement. These galaxies are 100 times more numerous than their more massive cousins, as well as 100 times fainter than those detected during previous deep-field surveys of the early universe.

Ordinarily, the galaxies would not have been detectable, but the investigators were able to discover them as part of the Hubble Frontier Fields mission, which uses a natural “zoom lens” in space to magnify the light from distant galaxies located behind it through a phenomenon known as gravitational lensing.

“There's always been a concern that we've only found the brightest of the distant galaxies,” explained lead researcher and assistant professor of physics and astronomy Brian Siana. “The bright galaxies, however, represent the tip of the iceberg.”

“We believe most of the stars forming in the early universe are occurring in galaxies we normally can't see at all. Now we have found those 'unseen' galaxies and we're really confident that we're seeing the rest of the iceberg,” he added.

Siana and his colleagues believe that they have completed the census of galaxies at a time when the universe was approximately 3.4 billion years old. If this newly discovered batch of galaxies is indicative of the entire population during this epoch, they believe that most new stars would have been formed in these miniature galaxies.

Discovering these galaxies helps support suggestions that hot stars in small galaxies produced enough radiation to ionize hydrogen by stripping off electrons in a process known as reionization. Experts believe that this would have occurred roughly 13 billion years ago, no more than one billion years after the formation of the universe.

“Though these galaxies are very faint, their increased numbers means that they account for the majority of star formation during this epoch,” explained graduate student and first author Anahita Alavi. “Although the galaxies in our sample existed a few billion years after reionization, it's presumed that galaxies like these, or possibly some of these galaxies, did play a big role in reionization.”

Siana, Alavi and their colleagues used Hubble's Wide Field Camera 3 instrument to hunt for faint, star-forming galaxies in ultraviolet light, which is said to be a reliable tracer of star birth. These galaxies existed during the universe’s “baby boom” of star formation, which is believed to have peaked between nine and 12 billion years ago.

In related news, NASA officials also announced the discovery of four unusually bright galaxies as they appeared 13 billion years ago, with the brightest one forming stars approximately 50 times faster than our galaxy does today. These galaxies are just five percent the size of the Milky Way, but are believed to contain about one billion stars.

These galaxies were discovered by the Hubble and Spitzer space telescopes, and are said to be 10 to 20 times more luminous than any object previously discovered during this early epoch, the space agency said. Astronomers first detected them using Hubble, and then estimated the total stellar luminosity of the galaxies using Spitzer.

“This is the first time scientists were able to measure an object's mass at such a huge distance,” said Yale University research fellow Pascal Oesch. “It's a fabulous demonstration of the synergy between Hubble and Spitzer.”

“The result bodes well for NASA's James Webb Space Telescope, currently in development,” NASA added. “Scientists anticipate using Webb to look even farther back in time to find young, growing galaxies as they existed only a few hundred million years after the universe began in theorized big bang.”