Hubble Frontier Fields view of MACSJ0717.5+3745
Hubble Frontier Fields view of Abell 2744
Observations by the NASA/ESA Hubble Space Telescope have taken advantage of gravitational lensing to reveal the largest sample of the faintest and earliest known galaxies in the Universe. Some of these galaxies formed just 600 million years after the Big Bang and are fainter than any other galaxy yet uncovered by Hubble. The team has determined, for the first time with some confidence, that these small galaxies were vital to creating the Universe that we see today.
An international team of astronomers, led by Hakim Atek of
the Ecole Polytechnique Fédérale de Lausanne, Switzerland, has
discovered over 250 tiny galaxies that existed only 600-900 million
years after the Big Bang [1]
— one of the largest samples of dwarf galaxies yet to be discovered at
these epochs. The light from these galaxies took over 12 billion years
to reach the telescope, allowing the astronomers to look back in time
when the universe was still very young.
Although impressive, the
number of galaxies found at this early epoch is not the team’s only
remarkable breakthrough, as Johan Richard from the Observatoire de
Lyon, France, points out, “The faintest galaxies detected in these
Hubble observations are fainter than any other yet uncovered in the
deepest Hubble observations.”
By looking at the light coming
from the galaxies the team discovered that the accumulated light
emitted by these galaxies could have played a major role in one of the
most mysterious periods of the Universe’s early history — the epoch of
reionisation. Reionisation started when the thick fog of hydrogen gas
that cloaked the early Universe began to clear. Ultraviolet light was
now able to travel over larger distances without being blocked and the
Universe became transparent to ultraviolet light [2].
By
observing the ultraviolet light from the galaxies found in this study
the astronomers were able to calculate whether these were in fact some
of the galaxies involved in the process. The team determined, for the
first time with some confidence, that the smallest and most abundant of
the galaxies in the study could be the major actors in keeping the
Universe transparent. By doing so, they have established that the epoch
of reionisation — which ends at the point when the Universe is fully
transparent — came to a close about 700 million years after the Big Bang
[3].
Lead author Atek explained, “If
we took into account only the contributions from bright and massive
galaxies, we found that these were insufficient to reionise the
Universe. We also needed to add in the contribution of a more abundant
population of faint dwarf galaxies.”
To make these
discoveries, the team utilised the deepest images of gravitational
lensing made so far in three galaxy clusters, which were taken as part
of the Hubble Frontier Fields programme [4].
These clusters generate immense gravitational fields capable of
magnifying the light from the faint galaxies that lie far behind the
clusters themselves. This makes it possible to search for, and study,
the first generation of galaxies in the Universe.
Jean-Paul Kneib, co-author of the study from the Ecole Polytechnique Fédérale de Lausanne, Switzerland, explains, “Clusters
in the Frontier Fields act as powerful natural telescopes and unveil
these faint dwarf galaxies that would otherwise be invisible.”
Co-author
of the study Mathilde Jauzac, from Durham University, UK, and the
University of KwaZulu-Natal, South Africa, remarks on the significance
of the discovery and Hubble’s role in it,“Hubble remains unrivalled
in its ability to observe the most distant galaxies. The sheer depth of
the Hubble Frontier Field data guarantees a very precise understanding
of the cluster magnification effect, allowing us to make discoveries
like these.”
These results highlight the impressive
possibilities of the Frontier Fields programme with more galaxies, at
even earlier time, likely to be revealed when Hubble peers at three more
of these galaxy clusters in the near future.
Notes
[1] The calculated redshift for these objects is between z = 6 and z = 8.
[2]
Neutral hydrogen gas absorbs all the high-energy ultraviolet light
emitted by hot young stars very efficiently. At the same time, the
absorbed ultraviolet light ionises the hydrogen. The very low density
ionised hydrogen gas filling the universe became fully transparent.The
hot stars carve out transparent bubbles in the gas and once all these
bubbles merge to fill all of space, reionisation is said to be complete
and the Universe becomes transparent to ultraviolet light.
[3] This corresponds to a redshift of about z = 7.5.
[4]
The Hubble Frontier Fields is a three-year, 840-orbit programme which
will yield the deepest views of the Universe to date, combining the
power of Hubble with the gravitational amplification of light around six
different galaxy clusters to explore more distant regions of space than
could otherwise be seen.
Notes for Editors
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
More Information
Image credit: NASA, ESA and the HST Frontier Fields team (STScI)
This
research was presented in a paper entitled “Are Ultra-faint Galaxies at
z = 6−8 Responsible for Cosmic Reionization? Combined Constraints from
the Hubble Frontier Fields Clusters And Parallels”, by H. Atek et al.,
to appear in the Astrophysical Journal.
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
The
international team of astronomers in this study consists of Hakim Atek
(Laboratoire d’Astrophysique, Ecole Polytechnique Fédérale de Lausanne,
Switzerland ; Department of Astronomy, Yale University, USA), Johan
Richard (CRAL, Observatoire de Lyon, France), Mathilde Jauzac (Institute
for Computational Cosmology, Durham University, UK; Astrophysics and
Cosmology Research Unit, University of KwaZulu-Natal, South Africa),
Jean-Paul Kneib (Laboratoire d’Astrophysique, Ecole Polytechnique
Fédérale de Lausanne, Switzerland; Aix Marseille Université, CNRS, LAM
UMR 7326, France), Priyamvada Natarajan (Department of Astronomy, Yale
University, USA), Marceau Limousin (Aix Marseille Université, CNRS, LAM
UMR 7326, France), Daniel Schaerer (Observatoire de Genève, Switzerland;
CNRS, IRAP, France), Eric Jullo (Aix Marseille Université, CNRS, LAM
UMR 7326, France), Harald Ebeling (Institute for Astronomy, University
of Hawaii, USA), Eiichi Egami (Steward Observatory, University of
Arizona, USA), and Benjamin Clement (CRAL, Observatoire de Lyon,
France).
Links
- Images of Hubble
- Frontier Fields programme
- Link to science paper
- Hubblecast 70: Peering around cosmic corners
Contacts
Hakim Atek
Laboratoire d’Astrophysique, Ecole Polytechnique Fédérale de Lausanne, Switzerland
Astronomy Departement, Yale University, USA
Tel: +1 203 645 82 23
Email: hakim.atek@epfl.ch
Johan Richard
Centre de Recherche Astrophysique de Lyon
Observatoire de Lyon, Université Lyon 1, France
Cell: +33 4 78 86 83 7
Email: johan.richard@univ-lyon1.fr
Mathilde Jauzac
Durham University, UK
University of KwaZulu-Natal, South Africa
Tel: +44 7445218614
Email: mathilde.jauzac@durham.ac.uk
Jean-Paul Kneib
Laboratoire d’Astrophysique, Ecole Polytechnique Fédérale de Lausanne, Switzerland
Laboratoire d’Astrophysique de Marseille, France
Tel: +41 22 3792473, +41 21 693 04 63, +33 695 795 392
Email: jean-paul.kneib@epfl.ch
Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Cell: +49 176 62397500
Email: mjaeger@partner.eso.org
Source: ESA/Hubble News
