A&A press release: Ubiquitous galaxies discovered in the Early Universe (8 March 2006)
- Published on 08 March 2006
A&A press release
Released on March 8th, 2006
Ubiquitous galaxies discovered in the Early Universe
Based on the article “Ultraviolet-to-far infrared properties of Lyman break galaxies and luminous infrared galaxies at z ~ 1”, by D. Burgarella et al.
(To be published in Astronomy & Astrophysics. )
This press release is issued as a collaboration with the Observatoire Astronomique de Marseille Provence and Astronomy & Astrophysics.
The astronomer Denis Burgarella (Observatoire Astronomique Marseille Provence, Laboratoire d’Astrophysique de Marseille, France) and his colleagues  from France, the USA, Japan, and Korea, have recently announced their discovery of new galaxies in the Early Universe both for the first time in the near-UV and in the far-infrared wavelengths. This discovery leads to the first thorough investigation of early galaxies. Figure 1 shows some of these new galaxies. The discovery will be reported in a coming issue of Astronomy & Astrophysics.
Fig. 1 - Examples of the new galaxies discovered at z~1.
The Lyman-break technique is based on the characteristic “disappearance” of distant galaxies observed in the far-UV wavelengths. As light from a distant galaxy is almost fully absorbed by hydrogen at 0.912 nm (due to the absorption lines of hydrogen, discovered by the physicist Theodore Lyman), the galaxy “disappears” in the far-ultraviolet filter. Figure 2 illustrates the “disappearance” of the galaxy in the far-UV filter. The Lyman discontinuity should theoretically occur at 0.912 nm. Photons at shorter wavelengths are absorbed by hydrogen around stars or within the observed galaxies. For high-redshift galaxies, the Lyman discontinuity is redshifted so that it occurs at a longer wavelength and can be observed from the Earth. From ground-based observations, astronomers can currently detect galaxies with a redshift range of z~3 to z~6. However, once detected, it is still very difficult to obtain additional information on these galaxies because they are very faint.
Fig. 2 - Illustration of the Lyman-break technique. The same galaxy observed at all wavelengths, from near-UV (NUV) to infrared (I) seems to “disappear” at the shortest wavelength in far-UV (left).
Previous observations of distant galaxies have led to the discovery of two classes of galaxies, one of which includes galaxies that emit light in the near-UV and visible wavelength ranges. The other type of galaxy emits light in the infrared (IR) and submillimeter ranges. The UV galaxies were not observed in the infrared range, while IR galaxies were not observed in the UV. It was thus difficult to explain how such galaxies could evolve into present-day galaxies that emit light at all wavelengths. With their work, Denis Burgarella and his colleagues have taken a step toward solving this problem. When observing their new sample of z~1 galaxies, they found that about 40% of these galaxies emit light in the infrared range as well. This is the first time a significant number of distant galaxies were observed both in the UV and IR wavelength ranges, incorporating the properties of both major types.
From their observations of this sample, the team also inferred various information about these galaxies. Combining UV and infrared measurements makes it possible to determine the formation rate for stars in these distant galaxies for the first time. Stars form there very actively, at a rate of a few hundred to one thousand stars per year (only a few stars currently form in our Galaxy each year). The team also studied their morphology, and show that most of them are spiral galaxies. Up to now, distant galaxies were believed to be mainly interacting galaxies, with irregular and complex shapes. Denis Burgarella and his colleagues have now shown that the galaxies in their sample, seen when the Universe had about 40% of its current age, have regular shapes, similar to present-day galaxies like ours. They bring a new element to our understanding of the evolution of the galaxies.
Ultraviolet-to-far infrared properties of Lyman break galaxies and luminous infrared galaxies at z ~ 1
by D. Burgarella, P.G. Perez-Gonzalez, K.D. Tyler, G.H. Rieke, V. Buat, T.T. Takeuchi, S. Lauger, S. Arnouts, O. Ilbert, T.A. Barlow, L. Bianchi, Y.-W. Lee, B.F. Madore, R.F. Malina, A.S. Szalay, Y.K. Yi
To be published in Astronomy & Astrophysics (DOI number:10.1051/0004-6361:20054309)
Dr Denis Burgarella
Observatoire Astronomique Marseille Provence
2, Place Le Verrier
13248 Marseille Cedex 04, France
Email: denis.burgarella (at) oamp.fr
Phone : +33 4 91 05 69 71
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Dr. Jennifer Martin
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© Astronomy & Astrophysics 2006