Galaxy Formation News & Comment!
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Message 16275 of 16275
From: "Todd S. Greene"
Date: Thu Jan 1, 2004 8:29 am
Subject: News Item - Observing galaxy formation several billion years
[posted by Todd Greene]
[full press release below; go to link for pictures; note line-wrapped
My comments: Even while astronomers are literally observing the distant
past, in these examples from around 9 billion and 12 billion
years ago, young earth creationists in their rhetoric pretend that
"evolutionists" (their propagandistic reference to astronomers,
among other scientists) cannot observe a distant past. When pressed
about this false rhetoric, young earth creationists retreat to their
totally unscientific Prankster God argument. So much for "scientific
The "vision clarity" of the technology used on the Hubble Space
Telescope makes possible the observations of the kinds of details
A Tale of Two Record-Breaking Galaxy Clusters
(Hubble Space Telescope Science Institute, 1/1/04)
Looking back in time nearly 9 billion years, an international team of
astronomers found mature galaxies in a young universe. The galaxies
are members of a cluster of galaxies that existed when the universe was
only 5 billion years old, or about 35 percent of its present age.
This compelling evidence that galaxies must have started forming just
after the big bang was bolstered by observations made by the same
team of astronomers when they peered even farther back in time. The team
found embryonic galaxies a mere 1.5 billion years after the
birth of the cosmos, or 10 percent of the universe's present age.
The "baby galaxies" reside in a still-developing cluster, the most
distant proto-cluster ever found.
The Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space
Telescope was used to make observations of the massive cluster, RDCS
1252.9-2927, and the proto-cluster, TN J1338-1942. Observations by
NASA's Chandra X-ray Observatory yielded the mass and heavy element
content of RDCS 1252, the most massive known cluster for that epoch.
These observations are part of a coordinated effort by the ACS science
team to track the formation and evolution of clusters of
galaxies over a broad range of cosmic time.
The ACS was built especially for studies of such distant objects. These
findings further support observations and theories that
galaxies formed relatively early in the history of the cosmos. The
existence of such massive clusters in the early universe agrees with
a cosmological model wherein clusters form from the merger of many
sub-clusters in a universe dominated by cold dark matter. The precise
nature of cold dark matter, however, is still not known.
The first Hubble study estimated that galaxies in RDCS 1252 formed the
bulk of their stars more than 11 billion years ago (at redshifts
greater than 3). The results were published in the Oct. 20, 2003 issue
of the Astrophysical Journal. The paper's lead author is John
Blakeslee of the Johns Hopkins University in Baltimore, Md.
The second Hubble study uncovered, for the first time, a proto-cluster
of "infant galaxies" that existed more than 12 billion years ago (at
redshift 4.1). These galaxies are so young that astronomers can still
see a flurry of stars forming within them. The galaxies are
grouped around one large galaxy. These results will be published in the
Jan. 1, 2004 issue of Nature. The paper's lead author is George Miley of
Leiden Observatory in the Netherlands.
"Until recently people didn't think that clusters existed when the
universe was only about 5 billion years old," Blakeslee explained.
"Even if there were such clusters," Miley added, "until recently
astronomers thought it was almost impossible to find clusters that
existed 8 billion years ago. In fact, no one really knew when clustering
began. Now we can witness it."
Both studies led the astronomers to conclude that these systems are the
progenitors of the galaxy clusters seen today. "The cluster RDCS
1252 looks like a present-day cluster," said Marc Postman of the Space
Telescope Science Institute in Baltimore, Md., and co-author of
both research papers. "In fact, if you were to put it next to a
present-day cluster, you wouldn't know which is which."
A Tale of Two Clusters
How can galaxies grow so fast after the big bang? "It is a case of the
rich getting richer," Blakeslee said. "These clusters grew
quickly because they are located in very dense regions, so there is
enough material to build up the member galaxies very fast."
This idea is strengthened by X-ray observations of the massive cluster
RDCS 1252. Chandra and the European Space Agency's XMM-Newton provided
astronomers with the most accurate measurements to date of
the properties of an enormous cloud of hot gas that pervades the massive
cluster. This 160-million-degree Fahrenheit (70-million-
degree Celsius) gas is a reservoir of most of the heavy elements in the
cluster and an accurate tracer of its total mass. A paper by
Piero Rosati of the European Southern Observatory (ESO) and colleagues
that presents the X-ray observations of RDCS 1252 will be published in
January 2004 in the Astronomical Journal.
"Chandra's sharp vision resolved the shape of the hot gas halo and
showed that RDCS 1252 is very mature for its age," said Rosati, who
discovered the cluster with the ROSAT X-ray telescope.
RDCS 1252 may contain many thousands of galaxies. Most of these
galaxies, however, are too faint to detect. But the powerful "eyes"
of the ACS pinpointed several hundred of them. Observations using ESO's
Very Large Telescope (VLT) provided a precise measurement of the
distance to the cluster. The ACS enabled the researchers to accurately
determine the shapes and colors of the 100 galaxies, providing
information on the ages of the stars residing in them. The ACS team
estimated that most of the stars in the cluster were already formed when
the universe was about 2 billion years old. X-ray observations,
furthermore, showed that 5 billion years after the big bang the
surrounding hot gas had been enriched with heavy elements from these
stars and had been swept away from the galaxies.
If most of the galaxies in RDCS 1252 have reached maturity and are
settling into a quiet adulthood, the forming galaxies in the distant
proto-cluster are in their energetic, unruly youth.
The proto-cluster TN J1338 contains a massive embryonic galaxy
surrounded by smaller developing galaxies, which look like dots in
the Hubble image. The dominant galaxy is producing spectacular
fueled by a supermassive black hole deep within the galaxy's nucleus.
Interaction between these jets and the gas can stimulate a torrent of
star birth. The energetic radio galaxy's discovery by radio telescopes
prompted astronomers to hunt for the smaller galaxies that make up the
"Massive clusters are the cities of the universe, and the radio galaxies
within them are the smokestacks we can use for finding them
when they are just beginning to form," Miley said.
The two findings underscore the power of combining observations from
many different telescopes that provided views of the distant universe in
a range of wavelengths. Hubble's advanced camera provided critical
information on the structure of both distant galaxy clusters.
Chandra's and XMM-Newton's X-ray vision furnished the essential
measurements of the primordial gas in which the galaxies in RDCS 1252
are embedded, and accurate estimates of the total mass contained within
that cluster. Large ground-based telescopes, like the VLT,
provided precise measurements of the distance of both clusters as well
as the chemical composition of the galaxies in them.
The ACS team is conducting further observations of distant clusters to
solidify our understanding of how these young clusters and their
galaxies evolve into the shape of things seen today. Their planned
observations include using near-infrared observations to analyze the
star-formation rates in some of the target clusters, including RDCS
1252, to measure the cosmic history of star formation in these
massive structures. The team is also searching the regions around
several ultra-distant radio galaxies for additional examples of proto-
clusters. The team's ultimate scientific goal is to establish a complete
picture of cluster evolution beginning with the formation at the
earliest epochs and detailing the evolution up to today.