|
An international team including astronomers
from the Institut d'Astrophysique Spatiale (IAS, CNRS - Université
de Paris 11), the Institut d'Astrophysique de Paris (CNRS - Université
de Paris 6) and the Institut de Radioastronomie Millimétrique (IRAM)
in Grenoble, as well as astronomers from Germany and the United States,
have just discovered huge gas and dust reservoirs in the most distant
quasar known. The detected radiation was emitted when the universe was
only one sixteenth of its current age, or 850 million years after the
Big Bang. These observations make it possible to study, for the very first
time, the conditions under which the first stars and black holes within
this type of galaxy were formed. These results are published in the July
24th issue of the journal Nature and in an article to be published in
Astronomy & Astrophysics.
"We were very surprised to detect such large quantities of heavy
elements in the distant past, not long after the Big Bang," says
Pierre Cox of the IAS. "Since carbon and oxygen and the elements
that form the specks of dust were created by thermonuclear reactions within
the stars, the enrichment of interstellar matter must have occurred very
rapidly, probably as a result of the explosion of the first most massive
stars."
Carbon monoxide (CO) was detected using an IRAM interferometer located
on the Plateau de Bure (France) and with the Very Large Array in New Mexico
(United States). Dust emission was observed using an IRAM 30-meter radio
telescope located on the Pico Veleta near Grenada (Spain).
The most distant quasar known at this time, which goes by the name of
J1148+5251, was discovered at the beginning of the year within the framework
of the Sloan Digital Sky Survey, a major astronomical survey project led
by Xiaohui Fan of the University of Arizona and his team. J1148+5251 is
a young galaxy with a super massive black hole at its center, several
billion times the mass of our sun. This quasar is one of the five objects
known at this time to be located at the end of the universe's "Dark
Age," a time when it became transparent and where galaxies, stars
and black holes formed with increasing rapidity. The discovery of molecular
gas and dust in this object therefore opens up the possibility, for the
very first time, of studying the conditions of stellar formation in detail
and determining physical and chemical conditions of the matter that made
up the galaxies at the beginning of the universe.
Molecular gas radiation reveals basic information about the density, temperature
and the size of the central region and the more active regions of this
galaxy that surround the central black hole, regions where a new star
is formed every five hours, a formation rate that is several thousand
times greater than the one in our local universe.
The quantities of molecular gas and dust detected indicate that the formation
mechanism must have been very effective and rapid at the cosmic scale.
The carbon and oxygen were created within the centers of the first stars
and the dust in the explosions at the end of the life of these very massive
stars.
"Ten years ago, no one could have ever imagined that gas and dust
reservoirs such as these had existed just after the Big Bang," recalls
Alain Omont (IAP). "Since original cosmic matter did not contain
these heavy elements, the first stars created in the universe must have
formed these elements and ejected them into the interstellar environment
with a great degree of efficiency, as a result of their violent winds
or during supernovae explosions at the end of their short lives. These
processes apparently made it possible to enrich the surrounding space
with heavy elements in proportions just about comparable to those that
we know today in the local universe, some 13 billion years later."
On the basis of the properties of the three CO lines detected in J1148+5251,
astronomers were able to estimate the size of the region containing atomic
hydrogen, a region measuring several thousand light years. "This
appears to be enormous," explains Pierre Cox of the IAS, "but
it is a region that is so small in the sky that no telescope is capable
of revealing the details of the quasar at this time. The detection of
CO provides us with a unique, albeit indirect, means of determining the
morphology, the density and the temperature of these exceptionally active
regions." Astronomers have therefore estimated that the quantity
of gas present in this quasar would be consumed in less that 10 million
years if the present star formation continued at the rate of one star
created every five hours. It is possible that an undetectable gas reservoir
exists, providing a continuous gas supply to J1148+5251 and allowing for
a longer stellar formation period. If not, the stellar formation activity
will progressively die out if there is no supply. "No one knows what
will happen after that," says Roberto Neri of IRAM. "We only
have this moment of J1148+5251. In order to better understand the causes
and evolution of star and black hole formation at the beginning of the
universe, we will have to find other similar objects, even more distant,
and compare their properties."
Although other discoveries in this field are possible using the VLA and
IRAM radio telescope networks in the near future, astronomers expect spectacular
results from the new radio interferometer, the Atacama Large Millimeter
Array (ALMA). This is a major project, based on international partnerships
between Europe, the United States, Canada and Chile, currently underway
in the Atacama Desert in Chile, which will be operational in 2011.
Publications:
F. Bertoldi, P. Cox, R. Neri, C.L. Carilli, F. Walter, A. Omont, A. Beelen,
C. Henkel, X. Fan, M.A. Strauss, K.M. Menten, "High-excitation CO
in a quasar host galaxy at z = 6.42," Astronomy and Astrophysics
Letters, (in press)
F. Walter, F. Bertoldi, C. Carilli, P. Cox, K.Y. Lo, R. Neri, X. Fan,
A. Omont, M.A. Strauss, K.M. Menten, "Molecular gas in the host galaxy
of a quasar at redshift z = 6.42," Nature, (July 24, 2003)
F. Bertoldi, C.L. Carilli, P. Cox, X. Fan, M.A. Strauss, A. Beelen, A.
Omont, R. Zylka, "Dust emission in z > 6 quasars," Astronomy
and Astrophysics Letters, (in press)
Researcher contacts:
Pierre Cox, IAS. Tel: +33 1 69 85 87 37. E-mail:
Pierre.Cox@ias.u-psud.fr
Alexandre Beelen, IAS. Tel: +33 1 60 85 85 76. E-mail: Alexandre.Beelen@ias.u-psud.fr
Roberto Neri, IRAM. Tel: +33 4 76 82 49 82. E-mail: neri@iram.fr
CNRS
Press contact:
Muriel Ilous
Tel: +33 1 44 96 43 09
E-mail: muriel.ilous@cnrs-dir.fr
INSU CNRS contact:
Philippe Chauvin
Tel: +33 1 44 96 43 36
E-mail: philippe.chauvin@cnrs-dir.fr
|