Galaxy Clusters MACS J0416.1-2403 and MACS J0717.5+3745 (Hubble, Chandra, and JVLA)
Credit: NASA, ESA, CXC, NRAO/AUI/NSF, STScI, R. van Weeren (Harvard-Smithsonian Center for Astrophysics), and G. Ogrean (Stanford University). Acknowledgment: NASA, ESA, J. Lotz (STScI), and the HFF team
Introduction: To learn more about galaxy clusters, including how they grow via
collisions, astronomers have used some of the world's most powerful
telescopes, looking at different types of light. They have focused long
observations with these telescopes on a half-dozen galaxy clusters. The
name for the galaxy cluster project is the "Frontier Fields." Two of these
Frontier Fields galaxy clusters, MACS J0416.1-2403 (abbreviated MACS
J0416) in the right panel and MACS J0717.5+3745 (MACS J0717 for short) in
the left panel, are featured here in a pair of multiwavelength images.
Located about 4.3 billion light-years from Earth, MACS J0416 is a pair of
colliding galaxy clusters that will eventually combine to form an even
bigger cluster. MACS J0717, one of the most complex and distorted galaxy
clusters known, is the site of a collision between four clusters. It is
located about 5.4 billion light-years away from Earth. These new images
of MACS J0416 and MACS J0717 contain data from three different
telescopes: NASA's Chandra X-ray Observatory (diffuse emission in blue),
Hubble Space Telescope (red, green, and blue), and the National Science
Foundation's Karl G. Jansky Very Large Array (diffuse emission in pink).
Where the X-ray and radio emission overlap the image appears purple.
Astronomers also used data from the Giant Metrewave Radio Telescope in
India in studying the properties of MACS J0416.
About image: Galaxy clusters are enormous collections of hundreds or even
thousands of galaxies and vast reservoirs of hot gas embedded in
massive clouds of dark matter, invisible material that does not emit or
absorb light, but can be detected through its gravitational effects.
These cosmic giants are not merely novelties of size or girth — rather
they represent pathways to understanding how our entire universe
evolved in the past and where it may be heading in the future.
To learn more about clusters, including how they grow via collisions,
astronomers have used some of the world's most powerful telescopes,
looking at different types of light. They have focused long observations
with these telescopes on a half-dozen galaxy clusters. The name for
the galaxy cluster project is the "Frontier Fields."
Two of these Frontier Fields galaxy clusters, MACS J0416.1-2403
(abbreviated MACS J0416) on the right panel and MACS J0717.5+3745 (MACS
J0717 for short) on the left panel, are featured here in a pair of
multiwavelength images.
Located about 4.3 billion light-years from Earth, MACS J0416 is a
pair of colliding galaxy clusters that will eventually combine to form
an even bigger cluster. MACS J0717, one of the most complex and
distorted galaxy clusters known, is the site of a collision between
four clusters. It is located about 5.4 billion light-years away from
Earth.
These new images of MACS J0416 and MACS J0717 contain data from
three different telescopes: NASA's Chandra X-ray Observatory (diffuse
emission in blue), Hubble Space Telescope (red, green, and blue), and
the National Science Foundation's Karl G. Jansky Very Large Array
(diffuse emission in pink). Where the X-ray and radio emission overlap
the image appears purple. Astronomers also used data from the Giant
Metrewave Radio Telescope in India in studying the properties of MACS
J0416.
The Chandra data show gas in the merging clusters with temperatures
of millions of degrees. The Hubble data show galaxies in the clusters
and other, more distant, galaxies lying behind the clusters. Some of
these background galaxies are highly distorted because of gravitational
lensing, the bending of light by massive objects. This effect can also
magnify the light from these objects, enabling astronomers to study
background galaxies that would otherwise be too faint to detect.
Finally, the structures in the radio data trace enormous shock waves
and turbulence. The shocks are similar to sonic booms, generated by the
mergers of the clusters.
New results from multiwavelength studies of MACS J0416 and MACS J0717, described in two separate papers, are included below.
MACS J0416
An open question for astronomers about MACS J0416 has been: Are we
seeing a collision in these clusters that is about to happen or one that
has already taken place? Until recently, scientists have been unable
to distinguish between these two explanations. Now, the combined data
from these various telescopes are providing new answers.
In MACS J0416 the dark matter (which leaves its gravitational imprint
in the optical data) and the hot gas (detected by Chandra) line up
well with each other. This suggests that the clusters have been caught
before colliding. If the clusters were being observed after colliding
the dark matter and hot gas should separate from each other, as seen in
the famous colliding cluster system known as the Bullet Cluster.
The cluster in the upper left contains a compact core of hot gas,
most easily seen in a specially processed image, and also shows
evidence of a nearby cavity, or hole in the X-ray-emitting gas. The
presence of these structures also suggests that a major collision has
not occurred recently, otherwise these features would likely have been
disrupted. Finally, the lack of sharp structures in the radio image
provides more evidence that a collision has not yet occurred.
In the cluster located in the lower right, the observers have noted a
sharp change in density on the southern edge of the cluster. This
change in density is most likely caused by a collision between this
cluster and a massive structure located further to the lower right.
MACS J0717
In Jansky Very Large Array images of this cluster, seven
gravitationally lensed sources are observed, all point sources or
sources that are barely larger than points. This makes MACS J0717 the
cluster with the highest number of known lensed radio sources. Two of
these lensed sources are also detected in the Chandra image. The
authors are only aware of two other lensed X-ray sources behind a
galaxy cluster.
All of the lensed radio sources are galaxies located between 7.8
billion and 10.4 billion light-years away from Earth. The brightness of
the galaxies at radio wavelengths shows that they contain stars
forming at high rates. Without the amplification by lensing, some of
these radio sources would be too faint to detect with typical radio
observations. The two lensed X-ray sources detected in the Chandra
images are likely active galactic nuclei (AGN) at the center of
galaxies. AGN are compact, luminous sources powered by gas heated to
millions of degrees as it falls toward supermassive black holes. These
two X-ray sources would have been detected without lensing, but would
have been two or three times fainter.
The large arcs of radio emission in MACS J0717 are very different
from those in MACS J0416 because of shock waves arising from the
multiple collisions occurring in the former object. The X-ray emission
in MACS J0717 has more clumps because there are four clusters violently
colliding.
Georgiana Ogrean, who was at the Harvard-Smithsonian Center for
Astrophysics while leading the work on MACS J0416, is currently at
Stanford University. The paper describing these results was published in
the October 20, 2015, issue of The Astrophysical Journal and is
available online. The research on MACS J0717 was led by Reinout van
Weeren from the Harvard-Smithsonian Center for Astrophysics and was
published in the February 1, 2016, issue of The Astrophysical Journal,
which is available online.
For more information about these new images, visit: http://chandra.si.edu/photo/2016/frontier/index.html
For additional information, contact:
Megan Watzke
Chandra X-ray Center, Cambridge, Massachusetts
617-496-7998
mwatzke@cfa.harvard.edu
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu
Source: HubbeSite
