ALMA Pinpoints Early Galaxies
The position of the Extended Chandra Deep Field South in the constellation of Fornax
ALMA Pinpoints Early Galaxies
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A team of astronomers has used the new
ALMA (Atacama Large Millimeter/submillimeter Array) telescope to
pinpoint the locations of over 100 of the most fertile star-forming
galaxies in the early Universe. ALMA is so powerful that, in just a few
hours, it captured as many observations of these galaxies as have been
made by all similar telescopes worldwide over a span of more than a
decade.
The most fertile bursts of star birth in the early Universe took
place in distant galaxies containing lots of cosmic dust. These galaxies
are of key importance to our understanding of galaxy formation and
evolution over the history of the Universe, but the dust obscures them
and makes them difficult to identify with visible-light telescopes. To
pick them out, astronomers must use telescopes that observe light at
longer wavelengths, around one millimetre, such as ALMA.
“Astronomers have waited for data like this for over a decade.
ALMA is so powerful that it has revolutionised the way that we can
observe these galaxies, even though the telescope was not fully
completed at the time of the observations,” said Jacqueline Hodge (Max-Planck-Institut für Astronomie, Germany), lead author of the paper presenting the ALMA observations.
The best map so far of these distant dusty galaxies was made using
the ESO-operated Atacama Pathfinder Experiment telescope (APEX). It
surveyed a patch of the sky about the size of the full Moon [1],
and detected 126 such galaxies. But, in the APEX images, each burst of
star formation appeared as a relatively fuzzy blob, which may be so
broad that it covered more than one galaxy in sharper images made at
other wavelengths. Without knowing exactly which of the galaxies are
forming the stars, astronomers were hampered in their study of star
formation in the early Universe.
Pinpointing the correct galaxies requires sharper observations, and
sharper observations require a bigger telescope. While APEX has a single
12-metre-diameter dish-shaped antenna, telescopes such as ALMA use
multiple APEX-like dishes spread over wide distances. The signals from
all the antennas are combined, and the effect is like that of a single,
giant telescope as wide as the whole array of antennas.
The team used ALMA to observe the galaxies from the APEX map during
ALMA’s first phase of scientific observations, with the telescope still
under construction. Using less than a quarter of the final complement of
66 antennas, spread over distances of up to 125 metres, ALMA needed
just two minutes per galaxy to pinpoint each one within a tiny region
200 times smaller than the broad APEX blobs, and with three times the
sensitivity. ALMA is so much more sensitive than other telescopes of its
kind that, in just a few hours, it doubled the total number of such
observations ever made.
Not only could the team unambiguously identify which galaxies had
regions of active star formation, but in up to half the cases they found
that multiple star-forming galaxies had been blended into a single blob
in the previous observations. ALMA’s sharp vision enabled them to
distinguish the separate galaxies.
“We previously thought the brightest of these galaxies were
forming stars a thousand times more vigorously than our own galaxy, the
Milky Way, putting them at risk of blowing themselves apart. The ALMA
images revealed multiple, smaller galaxies forming stars at somewhat
more reasonable rates,” said Alexander Karim (Durham University,
United Kingdom), a member of the team and lead author of a companion
paper on this work.
The results form the first statistically reliable catalogue of dusty
star-forming galaxies in the early Universe, and provide a vital
foundation for further investigations of these galaxies’ properties at
different wavelengths, without risk of misinterpretation due to the
galaxies appearing blended together.
Despite ALMA’s sharp vision and unrivalled sensitivity, telescopes such as APEX still have a role to play. “APEX
can cover a wide area of the sky faster than ALMA, and so it’s ideal
for discovering these galaxies. Once we know where to look, we can use
ALMA to locate them exactly,” concluded Ian Smail (Durham University, United Kingdom), co-author of the new paper.
Notes
[1] The observations were
made in a region of the sky in the southern constellation of Fornax (The
Furnace) called the Chandra Deep Field South. It has been extensively
studied already by many telescopes both on the ground and in space. The
new observations from ALMA extend the deep and high resolution
observations of this region into the millimetre/submillimetre part of
the spectrum and complement the earlier observations.
More information
The Atacama Large Millimeter/submillimeter
Array (ALMA), an international astronomy facility, is a partnership of
Europe, North America and East Asia in cooperation with the Republic of
Chile. ALMA is funded in Europe by the European Southern Observatory
(ESO), in North America by the U.S. National Science Foundation (NSF) in
cooperation with the National Research Council of Canada (NRC) and the
National Science Council of Taiwan (NSC) and in East Asia by the
National Institutes of Natural Sciences (NINS) of Japan in cooperation
with the Academia Sinica (AS) in Taiwan. ALMA construction and
operations are led on behalf of Europe by ESO, on behalf of North
America by the National Radio Astronomy Observatory (NRAO), which is
managed by Associated Universities, Inc. (AUI) and on behalf of East
Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint
ALMA Observatory (JAO) provides the unified leadership and management
of the construction, commissioning and operation of ALMA.
The Atacama Pathfinder Experiment (APEX) is a collaboration between
Max Planck Institut für Radioastronomie (MPIfR) at 50%, Onsala Space
Observatory (OSO) at 23% and the European Southern Observatory at 27%.
This research was presented in the paper “An ALMA Survey of
Submillimeter Galaxies in the Extended Chandra Deep Field South: Source
Catalog and Multiplicity”, by J. Hodge et al., to appear in the Astrophysical Journal.
The companion paper, “An ALMA survey of submillimetre galaxies in the
Extended Chandra Deep Field South: High resolution 870 μm source
counts”, on the multiplicity of the sources by A. Karim et al., will
appear in the Oxford University Press journal, Monthly Notices of the Royal Astronomical Society.
The team is composed of J. A. Hodge (Max-Planck-Institut für
Astronomie Heidelberg, Germany [MPIA]), A. Karim (Institute for
Computational Cosmology, Durham University, United Kingdom), I. Smail
(Durham), A. M. Swinbank (Durham), F. Walter (MPIA), A. D. Biggs (ESO),
R. J. Ivison (UKATC and Institute for Astronomy, University of
Edinburgh, Edinburgh, United Kingdom), A. Weiss (Max–Planck Institut für
Radioastronomie, Bonn, Germany), D. M. Alexander (Durham), F. Bertoldi
(Argelander–Institute of Astronomy, Bonn University, Germany), W. N.
Brandt (Institute for Gravitation and the Cosmos & Department of
Astronomy & Astrophysics, Pennsylvania State University, University
Park, USA), S. C. Chapman (Institute of Astronomy, University of
Cambridge, United Kingdom; Department of Physics and Atmospheric
Science, Dalhousie University, Halifax, United Kingdom), K. E. K. Coppin
(McGill University, Montreal, Canada), P. Cox (IRAM, Saint–Martin
d’Héres, France), A. L. R. Danielson (Durham), H. Dannerbauer
(University of Vienna, Austria), C. De Breuck (ESO), R. Decarli (MPIA),
A. C. Edge (Durham), T. R. Greve (University College London, United
Kingdom), K. K. Knudsen (Department of Earth and Space Sciences,
Chalmers University of Technology, Onsala Space Observatory, Onsala,
Sweden), K. M. Menten (Max-Planck-Institut für Radioastronomie, Bonn,
Germany), H.–W. Rix (MPIA), E. Schinnerer (MPIA), J. M. Simpson
(Durham), J. L. Wardlow (Department of Physics & Astronomy,
University of California, Irvine, USA) and P. van der Werf (Leiden
Observatory, Netherlands).
ESO is the foremost intergovernmental astronomy organisation in
Europe and the world’s most productive ground-based astronomical
observatory by far. It is supported by 15 countries: Austria, Belgium,
Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy,
the Netherlands, Portugal, Spain, Sweden, Switzerland and the United
Kingdom. ESO carries out an ambitious programme focused on the design,
construction and operation of powerful ground-based observing facilities
enabling astronomers to make important scientific discoveries. ESO also
plays a leading role in promoting and organising cooperation in
astronomical research. ESO operates three unique world-class observing
sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO
operates the Very Large Telescope, the world’s most advanced
visible-light astronomical observatory and two survey telescopes. VISTA
works in the infrared and is the world’s largest survey telescope and
the VLT Survey Telescope is the largest telescope designed to
exclusively survey the skies in visible light. ESO is the European
partner of a revolutionary astronomical telescope ALMA, the largest
astronomical project in existence. ESO is currently planning the
39-metre European Extremely Large optical/near-infrared Telescope, the
E-ELT, which will become “the world’s biggest eye on the sky”.
Links
- Research paper
- Photos of ALMA
- Press release from the Royal Astronomical Society (UK)
- Press release from MPIA (Heidelberg, Germany)
Contacts
Jacqueline HodgeMax-Planck-Institut für Astronomie
Heidelberg, Germany
Tel: +49 6221 528 467
Email: hodge@mpia.de
Alexander Karim
Institute for Computational Cosmology, Durham University
Durham, United Kingdom
Tel: +49 228 733658 (Christina Stein-Schmitz)
Email: alexander.karim@durham.ac.uk
Mark Swinbank
Institute for Computational Cosmology, Durham University
Durham, United Kingdom
Tel: +44 191 334 3772 (Lindsay Borrero)
Email: a.m.swinbank@durham.ac.uk
Richard Hook
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
