An international team of astronomers, including Dr. Harald Ebeling of the University of Hawaii at Manoa Institute for Astronomy, has used the Hubble Space Telescope to map the mass within a galaxy cluster, originally discovered with Maunakea telescopes, more precisely than ever before.
Clusters of galaxies are the most massive
objects in the universe, comprising hundreds to thousands of galaxies
and also enormous amounts of invisible dark matter. They grow through
collisions in which smaller clusters merge into ever more massive
systems, a process that can temporarily lead to highly complex mass
distributions.
Ebeling specializes in finding the rarest,
most extreme clusters that are the most rewarding targets for detailed
studies of the formation and evolution of cosmic structure. One of the
clusters discovered by Ebeling’s team in the course of the Massive
Cluster Survey (MACS), which used several telescopes on Maunakea, goes
by the unpoetic name of MACSJ0416.1-2403.
It was found to be so massive that the
cluster was selected for extremely deep observations with the Hubble
Space Telescope as part of the Frontier Fields program. The resulting Hubble data show the galaxy distribution within the cluster in stunning detail (Figure 1).
The new, ultra-deep observations also reveal a multitude of distorted
images of galaxies that are in fact far behind the cluster, bent and
often appearing multiple times within the Hubble image of MACSJ0416 due
to an effect called gravitational lensing, in which the mass of a
foreground object magnifies and distorts more distant objects.
Gravitational lensing by mass concentrations
in space comes in two varieties: so-called “strong lensing,” which
creates the highly elongated, almost linear images of distant background
galaxies visible near the center of the cluster (as predicted by
Einstein’s theory of relativity), and “weak lensing,” pioneered by IfA’s
Nick Kaiser in the 1990s, which causes much less perceptible, faint,
statistical distortions of hundreds of background galaxies viewed at
larger distances from the cluster core.
The spectacular images collected of MACSJ0416
during the Frontier Fields program were recently analyzed by members of
the team led by Mathilde Jauzac (Durham University, UK. and
Astrophysics & Cosmology Research Unit, South Africa). They used
both strong- and weak-lensing techniques to infer the cluster mass
distribution that creates the many lensing features identified in these
data.
Their meticulous search for even the faintest
gravitationally lensed images was unprecedentedly successful, resulting
in the identification of four times as many lensed background galaxies
as were previously known in this system. The result is a mass map of
MACSJ0416 that is more precise than any ever derived for any galaxy
cluster, showing the highly elongated distribution of dark matter in
this merging cluster in great detail and over an enormous range of
scales (Figure 2).
The study also established MACSJ0416 as a huge cluster indeed, with a
measured mass of 160 trillion times the mass of the sun.
“Our analysis of the Frontier Fields data
demonstrates impressively how detailed studies of the extremely massive
clusters found by MACS can advance our understanding not only of the
complexity of cluster formation but in fact of the distant universe
behind these powerful gravitational lenses,” explains Ebeling.
Further investigations of MACSJ0416 are underway, combining the Frontier Fields images with deep X-ray observations of the hot gas within the cluster and with spectroscopic redshifts of the cluster galaxies, measured by Ebeling as part of the follow-up work conducted by the MACS team using Maunakea facilities. Primary goal: to deduce the merger history of this extreme cluster by establishing its three-dimensional geometry and the trajectories of the clusters involved in the collision.
The results of the study will be published in
Monthly Notices of the Royal Astronomical Society in July 2014.
Additional information can be found in this press release by the
European Space Agency: http://www.spacetelescope.org/news/heic1416/.
Dr. Harald Ebeling
ebeling@ifa.hawaii.edu
Dr. Roy Gal
+1 808-956-6235
cell: +1 301-728-8637
rgal@ifa.hawaii.edu
Ms. Louise Good
Media Contact
+1 808-956-9403
good@ifa.hawaii.edu
Source: Institute for Astronomy - Universityof Hawaii
