Press release

 

Detection of giant gas and dust reservoirs in the most distant quasar

Paris, July 24, 2003

 


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