Nov. 15, 2012
J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov
Rob Gutro
Goddard Space Flight Center, Greenbelt, Md.
301-286-4044
robert.j.gutro@nasa.gov
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu
villard@stsci.edu
RELEASE: 12-397
NASA'S GREAT OBSERVATORIES FIND CANDIDATE FOR MOST DISTANT GALAXY
WASHINGTON -- By combining the power of NASA's Hubble and Spitzer
space telescopes and one of nature's own natural "zoom lenses" in
space, astronomers have set a new record for finding the most distant
galaxy seen in the universe.
The farthest galaxy appears as a diminutive blob that is only a tiny
fraction of the size of our Milky Way galaxy. But it offers a peek
back into a time when the universe was 3 percent of its present age
of 13.7 billion years. The newly discovered galaxy, named
MACS0647-JD, was observed 420 million years after the big bang, the
theorized beginning of the universe. Its light has traveled 13.3
billion years to reach Earth.
This find is the latest discovery from a program that uses natural
zoom lenses to reveal distant galaxies in the early universe. The
Cluster Lensing And Supernova Survey with Hubble (CLASH), an
international group led by Marc Postman of the Space Telescope
Science Institute in Baltimore, Md., is using massive galaxy clusters
as cosmic telescopes to magnify distant galaxies behind them. This
effect is called gravitational lensing.
Along the way, 8 billion years into its journey, light from
MACS0647-JD took a detour along multiple paths around the massive
galaxy cluster MACS J0647+7015. Without the cluster's magnification
powers, astronomers would not have seen this remote galaxy. Because
of gravitational lensing, the CLASH research team was able to observe
three magnified images of MACS0647-JD with the Hubble telescope. The
cluster's gravity boosted the light from the faraway galaxy, making
the images appear about eight, seven, and two times brighter than
they otherwise would that enabled astronomers to detect the galaxy
more efficiently and with greater confidence.
"This cluster does what no manmade telescope can do," said Postman.
"Without the magnification, it would require a Herculean effort to
observe this galaxy."
MACS0647-JD is so small it may be in the first steps of forming a
larger galaxy. An analysis shows the galaxy is less than 600
light-years wide. Based on observations of somewhat closer galaxies,
astronomers estimate that a typical galaxy of a similar age should be
about 2,000 light-years wide. For comparison, the Large Magellanic
Cloud, a dwarf galaxy companion to the Milky Way, is 14,000
light-years wide. Our Milky Way is 150,000 light-years across.
"This object may be one of many building blocks of a galaxy," said the
study's lead author, Dan Coe of the Space Telescope Science
Institute. "Over the next 13 billion years, it may have dozens,
hundreds, or even thousands of merging events with other galaxies and
galaxy fragments."
The galaxy was observed with 17 filters, spanning near-ultraviolet to
near-infrared wavelengths, using Hubble's Wide Field Camera 3 (WFC3)
and Advanced Camera for Surveys (ACS). Coe, a CLASH team member,
discovered the galaxy in February while poring over a catalogue of
thousands of gravitationally lensed objects found in Hubble
observations of 17 clusters in the CLASH survey. But the galaxy
appeared only in the two reddest filters.
"So either MACS0647-JD is a very red object, only shining at red
wavelengths, or it is extremely distant and its light has been
'redshifted' to these wavelengths, or some combination of the two,"
Coe said. "We considered this full range of possibilities."
The CLASH team identified multiple images of eight galaxies lensed by
the galaxy cluster. Their positions allowed the team to produce a map
of the cluster's mass, which is primarily composed of dark matter.
Dark matter is an invisible form of matter that makes up the bulk of
the universe's mass. "It's like a big puzzle," said Coe. "We have to
arrange the mass in the cluster so that it deflects the light of each
galaxy to the positions observed." The team's analysis revealed that
the cluster's mass distribution produced three lensed images of
MACS0647-JD at the positions and relative brightness observed in the
Hubble image.
Coe and his collaborators spent months systematically ruling out these
other alternative explanations for the object's identity, including
red stars, brown dwarfs, and red (old or dusty) galaxies at
intermediate distances from Earth. They concluded that a very distant
galaxy was the correct explanation.
The paper will appear in the Dec. 20 issue of The Astrophysical
Journal.
Redshift is a consequence of the expansion of space over cosmic time.
Astronomers study the distant universe in near-infrared light because
the expansion of space stretches ultraviolet and visible light from
galaxies into infrared wavelengths. Coe estimates MACS0647-JD has a
redshift of 11, the highest yet observed.
Images of the galaxy at longer wavelengths obtained with the Spitzer
Space Telescope played a key role in the analysis. If the object were
intrinsically red, it would appear bright in the Spitzer images.
Instead, the galaxy barely was detected, if at all, indicating its
great distance. The research team plans to use Spitzer to obtain
deeper observations of the galaxy, which should yield confident
detections as well as estimates of the object's age and dust content.
MACS0647-JD galaxy, however, may be too far away for any current
telescope to confirm the distance based on spectroscopy, which
spreads out an object's light into thousands of colors. Nevertheless,
Coe is confident the fledgling galaxy is the new distance champion
based on its unique colors and the research team's extensive
analysis.
"All three of the lensed galaxy images match fairly well and are in
positions you would expect for a galaxy at that remote distance when
you look at the predictions from our best lens models for this
cluster," Coe said.
The new distance champion is the second remote galaxy uncovered in the
CLASH survey, a multi-wavelength census of 25 hefty galaxy clusters
with Hubble's ACS and WFC3. Earlier this year, the CLASH team
announced the discovery of a galaxy that existed when the universe
was 490 million years old, 70 million years later than the new
record-breaking galaxy. So far, the survey has completed observations
for 20 of the 25 clusters.
The team hopes to use Hubble to search for more dwarf galaxies at
these early epochs. If these infant galaxies are numerous, then they
could have provided the energy to burn off the fog of hydrogen that
blanketed the universe, a process called re-ionization. Re-ionization
ultimately made the universe transparent to light.
For images and more information about the study, visit:
http://www.nasa.gov/hubble
and
http://hubblesite.org/news/2012/36
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