Location of the distant dusty galaxy A1689-zD1 behind the galaxy cluster Abell 1689 (annotated)
Infrared/visible-light view of the distant dusty galaxy A1689-zD1 behind the galaxy cluster Abell 1689
The distant dusty galaxy A1689-zD1 behind the galaxy cluster Abell 1689
Wide-field view of the sky around the rich galaxy cluster Abell 1689
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ALMA and VLT probe surprisingly dusty and evolved galaxy
One of the most distant galaxies ever
observed has provided astronomers with the first detection of dust in
such a remote star-forming system and tantalising evidence for the rapid
evolution of galaxies after the Big Bang. The new observations have
used ALMA to pick up the faint glow from cold dust in the galaxy
A1689-zD1 and used ESO’s Very Large Telescope to measure its distance.
A team of astronomers, led by Darach Watson from the University of Copenhagen, used the Very Large Telescope’s X-shooter instrument along with the Atacama Large Millimeter/submillimeter Array
(ALMA) to observe one of the youngest and most remote galaxies ever
found. They were surprised to discover a far more evolved system than
expected. It had a fraction of dust similar to a very mature galaxy,
such as the Milky Way. Such dust is vital to life, because it helps form
planets, complex molecules and normal stars.
The target of their observations is called A1689-zD1 [1]. It is observable only by virtue of its brightness being amplified more than nine times by a gravitational lens in the form of the spectacular galaxy cluster, Abell 1689,
which lies between the young galaxy and the Earth. Without the
gravitational boost, the glow from this very faint galaxy would have
been too weak to detect.
We are seeing A1689-zD1 when the Universe was only about 700 million years old — five percent of its present age [2].
It is a relatively modest system — much less massive and luminous than
many other objects that have been studied before at this stage in the
early Universe and hence a more typical example of a galaxy at that
time.
A1689-zD1 is being observed as it was during the period of reionisation,
when the earliest stars brought with them a cosmic dawn, illuminating
for the first time an immense and transparent Universe and ending the
extended stagnation of the Dark Ages.
Expected to look like a newly formed system, the galaxy surprised the
observers with its rich chemical complexity and abundance of
interstellar dust.
“After confirming the galaxy’s distance using the VLT,” said Darach Watson, “we
realised it had previously been observed with ALMA. We didn’t expect to
find much, but I can tell you we were all quite excited when we
realised that not only had ALMA observed it, but that there was a clear
detection. One of the main goals of the ALMA Observatory was to find
galaxies in the early Universe from their cold gas and dust emissions —
and here we had it!”
This galaxy was a cosmic infant — but it proved to be precocious. At
this age it would be expected to display a lack of heavier chemical
elements — anything heavier than hydrogen and helium, defined in
astronomy as metals.
These are produced in the bellies of stars and scattered far and wide
once the stars explode or otherwise perish. This process needs to be
repeated for many stellar generations to produce a significant abundance
of the heavier elements such as carbon, oxygen and nitrogen.
Surprisingly, the galaxy A1689-zD1 seemed to be emitting a lot of radiation in the far infrared [3],
indicating that it had already produced many of its stars and
significant quantities of metals, and revealed that it not only
contained dust, but had a dust-to-gas ratio that was similar to that of
much more mature galaxies.
“Although the exact origin of galactic dust remains obscure,” explains Darach Watson, “our
findings indicate that its production occurs very rapidly, within only
500 million years of the beginning of star formation in the Universe — a
very short cosmological time frame, given that most stars live for
billions of years.”
The findings suggest A1689-zD1 to have been consistently forming
stars at a moderate rate since 560 million years after the Big Bang, or
else to have passed through its period of extreme starburst very rapidly before entering a declining state of star formation.
Prior to this result, there had been concerns among astronomers that
such distant galaxies would not be detectable in this way, but A1689-zD1
was detected using only brief observations with ALMA.
Kirsten Knudsen (Chalmers University of Technology, Sweden), co-author of the paper, added, “This
amazingly dusty galaxy seems to have been in a rush to make its first
generations of stars. In the future, ALMA will be able to help us to
find more galaxies like this, and learn just what makes them so keen to
grow up.”
Notes
[1] This galaxy was noticed earlier in the Hubble images, and suspected to be very distant, but the distance could not be confirmed at that time.
[2] This corresponds to a redshift of 7.5.
[3] This radiation is stretched by the expansion of the Universe into the millimetre wavelength range by the time it gets to Earth and hence can be detected with ALMA.
More Information
This research was presented in a paper
entitled “A dusty, normal galaxy in the epoch of reionization” by D.
Watson et al., to appear online in the journal Nature on 2 March 2015.
The team is composed of D. Watson (Niels Bohr Institute, University
of Copenhagen, Denmark), L. Christensen (University of Copenhagen), K.
K. Knudsen (Chalmers University of Technology, Sweden), J. Richard
(CRAL, Observatoire de Lyon, Saint Genis Laval, France), A. Gallazzi
(INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy) and M. J.
Michalowski (SUPA, Institute for Astronomy, University of Edinburgh,
Royal Observatory, Edinburgh, UK).
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 16 countries: Austria, Belgium,
Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy,
the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the
United Kingdom, along with the host state of Chile. 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 a major partner in ALMA, the largest astronomical
project in existence. And on Cerro Armazones, close to Paranal, ESO is
building the 39-metre European Extremely Large Telescope, the E-ELT,
which will become “the world’s biggest eye on the sky”.
Links
Links
Contacts
Darach Watson
Niels Bohr Institute
University of Copenhagen, Denmark
Tel: +45 2480 3825
Email: darach@dark-cosmology.dk
Kirsten K. Knudsen
Chalmers University of Technology
Onsala, Sweden
Tel: +46 31 772 5526
Cell: +46 709 750 956
Email: kirsten.knudsen@chalmers.se
Richard Hook
ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
