Andrew Yee
March 8th 06, 02:59 PM
Journal Astronomy & Astrophysics
Les Ulis, France
Contact persons:
Science:
Dr Denis Burgarella
Observatoire Astronomique Marseille Provence
2, Place Le Verrier
13248 Marseille Cedex 04, France
Phone : +33 4 91 05 69 71
Press office:
Dr. Jennifer Martin
Journal Astronomy & Astrophysics
61, avenue de l'Observatoire
75014 Paris, France
Phone: +33 1 43 29 05 41
Press Release: March 8th, 2006
This press release is issued as a collaboration with the Observatoire
Astronomique de Marseille Provence and Astronomy & Astrophysics.
Ubiquitous galaxies discovered in the Early Universe
A team of astronomers from France, the USA, Japan, and Korea, led by Denis
Burgarella has recently discovered new galaxies in the Early Universe.
They have been detected for the first time both in the near-UV and in the
far-infrared wavelengths. Their findings will be reported in a coming
issue of Astronomy & Astrophysics. This discovery is a new step in
understanding how galaxies evolve.
The astronomer Denis Burgarella (Observatoire Astronomique Marseille
Provence, Laboratoire d'Astrophysique de Marseille, France) and his
colleagues [1] 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.
The knowledge of early galaxies has made major progress in the past ten
years. From the end of 1995, astronomers have been using a new technique,
known as the "Lyman-break technique". This technique allows very distant
galaxies to be detected. They are seen as they were when the Universe was
much younger, thus providing clues to how galaxies formed and evolved. The
Lyman-break technique has moved the frontier of distant galaxy surveys
further up to redshift z=6-7 (that is about 5% of the present age of the
Universe). In astronomy, the redshift denotes the shift of a light wave
from a galaxy moving away from the Earth. The light wave is shifted toward
longer wavelengths, that is, toward the red end of the spectrum. The
higher the redshift of a galaxy is, the farther it is from us.
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.
For the first time, Denis Burgarella and his team have been able to detect
less distant galaxies via the Lyman-break technique. The team collected
data from various origins: UV data from the NASA GALEX satellite, infrared
data from the SPITZER satellite, and data in the visible range at ESO
telescopes. From these data, they selected about 300 galaxies showing a
far-UV disappearance. These galaxies have a redshift ranging from 0.9 to
1.3, that is, they are observed at a moment when the Universe had less
than half of its current age. This is the first time a large sample of
Lyman Break Galaxies is discovered at z~1. As these galaxies are less
distant than the samples observed up to now, they are also brighter and
easier to study at all wavelengths thereby allowing a deep analysis from
UV to infrared to be performed.
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.
[1] The team includes D. Burgarella, V. Buat, T.T. Takeuchi, S. Lauger, S.
Arnouts, R.F. Malina (France), P.G. Pérez-Gonzales, K.D. Tyler, G.H.
Rieke, T.A. Barlow, L. Bianchi, B.F. Madore, A.S. Szalay (USA), Y.-W. Lee,
S.K. Yi (Korea), O. Ilbert (Italy).
"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)
Full article available in PDF format,
http://www.edpsciences.org/articles/aa/pdf/press-releases/PRAA200604.pdf
IMAGE CAPTIONS:
[Fig. 1:
http://www.edpsciences.org/papers/aa/abs/press-releases/PRaa200604/fig1.jpg
(39KB)]
Examples of the new galaxies discovered at z~1.
[Fig. 2:
http://www.edpsciences.org/papers/aa/abs/press-releases/PRaa200604/fig2.jpg
(41KB)]
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).
Les Ulis, France
Contact persons:
Science:
Dr Denis Burgarella
Observatoire Astronomique Marseille Provence
2, Place Le Verrier
13248 Marseille Cedex 04, France
Phone : +33 4 91 05 69 71
Press office:
Dr. Jennifer Martin
Journal Astronomy & Astrophysics
61, avenue de l'Observatoire
75014 Paris, France
Phone: +33 1 43 29 05 41
Press Release: March 8th, 2006
This press release is issued as a collaboration with the Observatoire
Astronomique de Marseille Provence and Astronomy & Astrophysics.
Ubiquitous galaxies discovered in the Early Universe
A team of astronomers from France, the USA, Japan, and Korea, led by Denis
Burgarella has recently discovered new galaxies in the Early Universe.
They have been detected for the first time both in the near-UV and in the
far-infrared wavelengths. Their findings will be reported in a coming
issue of Astronomy & Astrophysics. This discovery is a new step in
understanding how galaxies evolve.
The astronomer Denis Burgarella (Observatoire Astronomique Marseille
Provence, Laboratoire d'Astrophysique de Marseille, France) and his
colleagues [1] 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.
The knowledge of early galaxies has made major progress in the past ten
years. From the end of 1995, astronomers have been using a new technique,
known as the "Lyman-break technique". This technique allows very distant
galaxies to be detected. They are seen as they were when the Universe was
much younger, thus providing clues to how galaxies formed and evolved. The
Lyman-break technique has moved the frontier of distant galaxy surveys
further up to redshift z=6-7 (that is about 5% of the present age of the
Universe). In astronomy, the redshift denotes the shift of a light wave
from a galaxy moving away from the Earth. The light wave is shifted toward
longer wavelengths, that is, toward the red end of the spectrum. The
higher the redshift of a galaxy is, the farther it is from us.
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.
For the first time, Denis Burgarella and his team have been able to detect
less distant galaxies via the Lyman-break technique. The team collected
data from various origins: UV data from the NASA GALEX satellite, infrared
data from the SPITZER satellite, and data in the visible range at ESO
telescopes. From these data, they selected about 300 galaxies showing a
far-UV disappearance. These galaxies have a redshift ranging from 0.9 to
1.3, that is, they are observed at a moment when the Universe had less
than half of its current age. This is the first time a large sample of
Lyman Break Galaxies is discovered at z~1. As these galaxies are less
distant than the samples observed up to now, they are also brighter and
easier to study at all wavelengths thereby allowing a deep analysis from
UV to infrared to be performed.
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.
[1] The team includes D. Burgarella, V. Buat, T.T. Takeuchi, S. Lauger, S.
Arnouts, R.F. Malina (France), P.G. Pérez-Gonzales, K.D. Tyler, G.H.
Rieke, T.A. Barlow, L. Bianchi, B.F. Madore, A.S. Szalay (USA), Y.-W. Lee,
S.K. Yi (Korea), O. Ilbert (Italy).
"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)
Full article available in PDF format,
http://www.edpsciences.org/articles/aa/pdf/press-releases/PRAA200604.pdf
IMAGE CAPTIONS:
[Fig. 1:
http://www.edpsciences.org/papers/aa/abs/press-releases/PRaa200604/fig1.jpg
(39KB)]
Examples of the new galaxies discovered at z~1.
[Fig. 2:
http://www.edpsciences.org/papers/aa/abs/press-releases/PRaa200604/fig2.jpg
(41KB)]
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).