Hubble Space Telescope image of the center
of the newly-confirmed JKCS 041 galaxy cluster, located at a distance of
9.9 billion light years. The galaxies located in the cluster are
circled. Blue circles show the few galaxies that continue to form new
stars, while yellow circles show those that have already entered
quiescence. A larger version is available here.
Pasadena, CA - The structures and star populations of
massive galaxies appear to change as they age, but much about how these
galaxies formed and evolved remains mysterious. Many of the oldest and
most massive galaxies reside in clusters, enormous structures where
numerous galaxies are found concentrated together. Galaxy clusters in
the early universe are thought to be key to understanding the lifecycles
of old galaxies, but to date astronomers have located only a handful of
these rare, distant structures.
New research from a team led by Carnegie’s Andrew Newman has
confirmed the presence of an unusually distant galaxy cluster, JKCS 041.
It is published by The Astrophysical Journal.
“Our observations make this galaxy cluster one of the best-studied structures from the early universe,” Newman said.
Although the team began studying JKCS 041 in 2006, it has taken years
of observing with many of the world’s most powerful telescopes to
finally confirm its distance. The team used the Hubble Space Telescope
to capture sharp images of the distant cluster and split the starlight
from the galaxies into its constituent colors, a technique known as
spectroscopy. They found 19 galaxies at precisely the same great
distance of 9.9 billion light years, the tell-tale sign of an early
galaxy cluster.
A previous study using the Chandra X-ray Observatory discovered X-ray emissions in the location of JKCS 041.
“These X-rays likely originate from hot gas in JKCS 041, which has
been heated to a temperature of about 80 million degrees by the gravity
of the massive cluster,” said team member Stefano Andreon of the
Osservatorio Astronomico di Brera, who led a companion paper published
by Astronomy & Astrophysics.
Today the largest and oldest galaxies are found in clusters, but
there is a mystery about when and why these giant galaxies stopped
forming new stars and became dormant, or quiescent. Peering back to a
time when the galaxies in JKCS 041 were only 1 billion years old---or 10
percent of their present age---the team found that most had already
entered their quiescent phase.
“Because JKCS 041 is the most-distant known cluster of its size, it
gives us a unique opportunity to study these old galaxies in detail and
better understand their origins,” Newman said.
Once massive galaxies enter their quiescent phase, they continue
expanding in overall size. This is thought to occur as galaxies collide
with one another and evolve into a new, larger galaxy. Early clusters
are suspected to be prime locations for these collisions, but to the
team’s surprise they found that the galaxies in JKCS 041 were growing at
nearly the same rate as non-cluster galaxies.
The international team included Newman, Andreon, Ginevra Trinchieri
of the Osservatorio Astronomico di Brera, Richard Ellis of Caltech,
Tommaso Treu of the University of California at Santa Barbara, and Anand
Raichoor of the Observatorie di Paris.
This work was based on observations made with the NASA/ESA Hubble
Space Telescope, obtained at the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS 5-26555. These observations are
associated with program number GO-12927, which was supported under NASA
contract NAS 5-26555. The work was also supported by the agreement
ASI-INAF I/009/10/0 and the Osservatorio Astronomico di Brera.
The Astrophysical Journal paper is available here.
The Astronomy & Astrophysics sister paper is available here.
Source: Carnagie Institution Science
