ALMA images of gravitationally-lensed distant star-forming galaxies
Gravitational lensing of distant star-forming galaxies (schematic)
Videos
Record-breaking haul of distant galaxies includes most distant detection of water published to date
Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) show that the most vigorous bursts of star birth in the cosmos took place much earlier than previously thought. The results are published in a set of papers to appear in the journal Nature on 14 March 2013, and in the Astrophysical Journal. The research is the most recent example of the discoveries coming from the new international ALMA observatory, which celebrates its inauguration today.
Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) show that the most vigorous bursts of star birth in the cosmos took place much earlier than previously thought. The results are published in a set of papers to appear in the journal Nature on 14 March 2013, and in the Astrophysical Journal. The research is the most recent example of the discoveries coming from the new international ALMA observatory, which celebrates its inauguration today.
The most intense bursts of star birth are thought to have occurred in
the early Universe, in massive, bright galaxies. These starburst
galaxies convert vast reservoirs of cosmic gas and dust into new stars
at a furious pace — many hundreds of times faster than in stately spiral
galaxies like our own galaxy, the Milky Way. By looking far into space,
at galaxies so distant that their light has taken many billions of
years to reach us, astronomers can observe this busy period in the
Universe’s youth.
“The more distant the galaxy, the further back in time one is
looking, so by measuring their distances we can piece together a
timeline of how vigorously the Universe was making new stars at
different stages of its 13.7 billion year history,” said Joaquin
Vieira (California Institute of Technology, USA), who led the team and
is lead author of the paper in the journal Nature.
The international team of researchers first discovered these distant
and enigmatic starburst galaxies with the US National Science
Foundation’s 10-metre South Pole Telescope (SPT) and then used ALMA to
zoom in on them to explore the stellar baby boom in the young Universe.
They were surprised to find that many of these distant dusty
star-forming galaxies are even further away than expected. This means
that, on average, their bursts of star birth took place 12 billion years
ago, when the Universe was just under 2 billion years old — a full
billion years earlier than previously thought.
Two of these galaxies are the most distant of their kind ever seen —
so distant that their light began its journey when the Universe was only
one billion years old. What’s more, in one of these record-breakers,
water is among the molecules detected, marking the most distant
observations of water in the cosmos published to date.
The team used the unrivalled sensitivity of ALMA to capture light
from 26 of these galaxies at wavelengths of around three millimetres.
Light at certain specific wavelengths can be produced by gas molecules
in these galaxies, and the wavelengths are stretched by the expansion of
the Universe over the billions of years that it takes the light to
reach us. By measuring the stretched wavelengths, astronomers can
calculate how long the light’s journey has taken, and place each galaxy
at the right point in cosmic history.
“ALMA’s sensitivity and wide wavelength range mean we could make
our measurements in just a few minutes per galaxy — about one hundred
times faster than before,” said Axel Weiss (Max-Planck-Institut für
Radioastronomie in Bonn, Germany), who led the work to measure the
distances to the galaxies. “Previously, a measurement like this
would have been a laborious process of combining data from both
visible-light and radio telescopes.”
In the majority of cases, the ALMA observations alone could pinpoint
the distances, but for a few galaxies the team combined the ALMA data
with measurements from other telescopes, including the Atacama
Pathfinder Experiment (APEX) and ESO’s Very Large Telescope [1].
The astronomers were using only a partial array of 16 of ALMA’s full
complement of 66 giant antennas, as the observatory was still under
construction at an altitude of 5000 metres on the remote Chajnantor
Plateau in the Chilean Andes. When complete, ALMA will be even more
sensitive, and will be able to detect even fainter galaxies. For now,
astronomers targeted the brighter ones. They took advantage of a helping
hand from nature, too: using gravitational lensing, an effect predicted
by Einstein’s general theory of relativity, where light from a distant
galaxy is distorted by the gravitational influence of a nearer
foreground galaxy, which acts like a lens and makes the distant source
appear brighter.
To understand by precisely how much this gravitational lensing
brightened the view of the galaxies, the team made sharper images of
them using more ALMA observations at wavelengths of around 0.9
millimetres.
"These beautiful pictures from ALMA show the background galaxies
warped into multiple arcs of light known as Einstein rings, which
encircle the foreground galaxies," said Yashar Hezaveh (McGill University, Montreal, Canada), who led the study of the gravitational lensing. “We
are using the massive amounts of dark matter surrounding galaxies
half-way across the Universe as cosmic telescopes to make even more
distant galaxies appear bigger and brighter.”
Analysis of the distortion reveals that some of the distant
star-forming galaxies are as bright as 40 trillion (40 million million)
Suns, and that gravitational lensing has magnified this by up to 22
times.
“Only a few gravitationally lensed galaxies have been found
before at these submillimetre wavelengths, but now SPT and ALMA have
uncovered dozens of them.” said Carlos De Breuck (ESO), a member of the team. “This
kind of science was previously done mostly at visible-light wavelengths
with the Hubble Space Telescope, but our results show that ALMA is a
very powerful new player in the field.”
"This is an great example of astronomers from around the world
collaborating to make an amazing discovery with a state-of-the-art
facility," said team member Daniel Marrone (University of Arizona, USA). "This
is just the beginning for ALMA and for the study of these starburst
galaxies. Our next step is to study these objects in greater detail and
figure out exactly how and why they are forming stars at such prodigious
rates."
Notes
[1] The additional observations were
made by APEX, the VLT, the Australia Telescope Compact Array (ATCA) and
the Submillimeter Array (SMA).
More information
The research is described in the paper
“Dusty starburst galaxies in the early Universe as revealed by
gravitational lensing”, by J. Vieira et al., in the journal Nature.
The work to measure the distances to the galaxies is described in the
paper “ALMA redshifts of millimeter-selected galaxies from the SPT
survey: The redshift distribution of dusty star-forming galaxies”, by A.
Weiss et al., in the Astrophysical Journal. The study of the
gravitational lensing is described in the paper “ALMA observations of
strongly lensed dusty star-forming galaxies”, by Y. Hezaveh et al., also
in the Astrophysical Journal.
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.
ESO is the foremost intergovernmental astronomy organisation in
Europe and the world’s most productive astronomical observatory. 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 by J. Vieira et al.
- Research paper by A. Weiss et al. on the work to measure the distances to the galaxies
- Research paper by Y. Hezaveh et al. on the study of the gravitational lensing
- More about ALMA at ESO
- The Joint ALMA Observatory
- Images of ALMA
- Videos of ALMA
Contacts
Axel WeissMax-Planck-Institut für Radioastronomie
Bonn, Germany
Tel: +49 228 525 273
Email: aweiss@mpifr-bonn.mpg.de
Joaquin Vieira
California Institute of Technology
USA
Cell: +1 949 887 5795
Email: vieira@caltech.edu
Yashar Hezaveh
McGill University
Montréal, Canada
Tel: +1 514 398 7032
Email: yasharh@physics.mcgill.ca
Richard Hook
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Douglas Pierce-Price
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6759
Email: dpiercep@eso.org
Carlos de Breuck
ESO
Garching bei München, Germany
Tel: +49 89 3200 6613
Email: cdebreuc@eso.org
Charles E. Blue
National Radio Astronomy Observatory, Public Information Officer
Charlottesville, USA
Tel: +1 434 296 0314
Email: cblue@nrao.edu
