Artist's impression of a protocluster forming in the early Universe
APEX view of the region around the Spiderweb Galaxy
The Spiderweb Galaxy and its surroundings (full ACS view)
Wide-field image of the Spiderweb Galaxy (ground-based image)
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Videos
APEX reveals hidden star formation in protocluster
Galaxy clusters are the largest objects in the Universe held together
by gravity but their formation is not well understood. The Spiderweb Galaxy (formally known as MRC 1138-262 [1]) and its surroundings have been studied for twenty years, using ESO and other telescopes [2], and is thought to be one of the best examples of a protocluster in the process of assembly, more than ten billion years ago.
But Helmut Dannerbauer (University of Vienna, Austria) and his team
strongly suspected that the story was far from complete. They wanted to
probe the dark side of star formation and find out how much of the star
formation taking place in the Spiderweb Galaxy cluster was hidden from
view behind dust.
The team used the LABOCA camera on the APEX telescope
in Chile to make 40 hours of observations of the Spiderweb Cluster at
millimetre wavelengths — wavelengths of light that are long enough to
peer right through most of the thick dust clouds. LABOCA has a wide
field and is the perfect instrument for this survey.
Carlos De Breuck (APEX project scientist at ESO, and a co-author of the new study) emphasises: “This
is one of the deepest observations ever made with APEX and pushes the
technology to its limits — as well as the endurance of the staff working
at the high-altitude APEX site, 5050 metres above sea level.”
The APEX observations revealed that there were about four times as
many sources detected in the area of the Spiderweb compared to the
surrounding sky. And by carefully comparing the new data with
complementary observations made at different wavelengths they were able
to confirm that many of these sources were at the same distance as the
galaxy cluster itself and must be parts of the forming cluster.
Helmut Dannerbauer explains: “The new APEX observations add the
final piece needed to create a complete census of all inhabitants of
this mega star city. These galaxies are in the process of formation so,
rather like a construction site on Earth, they are very dusty.”
But a surprise awaited the team when they looked at where the newly
detected star formation was taking place. They were expecting to find
this star formation region on the large filaments connecting galaxies.
Instead, they found it concentrated mostly in a single region, and that
region is not even centred on the central Spiderweb Galaxy in the
protocluster [3].
Helmut Dannerbauer concludes: “We aimed to find the hidden star
formation in the Spiderweb cluster — and succeeded — but we unearthed a
new mystery in the process; it was not where we expected! The mega city
is developing asymmetrically.”
To continue the story further observations are needed — and ALMA will be the perfect instrument to take the next steps and study these dusty regions in far greater detail.
Notes
[1] The Spiderweb Galaxy contains a
supermassive black hole and is a powerful source of radio waves — which
is what led astronomers to notice it in the first place.
[2] This region had been intensively observed by a
variety of ESO telescopes since the mid-1990s. The redshift (and hence
the distance) of the radio galaxy MRC1138-262 (the Spiderweb Galaxy) was
first measured at La Silla. The first visitor mode FORS observations on the VLT discovered the protocluster and afterwards further observations were made with ISAAC, SINFONI, VIMOS and HAWK-I.
The APEX LABOCA data complement optical and near-infrared datasets from
ESO telescopes. The team also used a 12-hour VLA image to
cross-identify the LABOCA sources in the optical images.
[3] These dusty starbursts are thought to evolve into
elliptical galaxies like those seen around us today in nearby galaxy
clusters.
More information
This research was presented in a paper, “An
excess of dusty starbursts related to the Spiderweb galaxy”, by
Dannerbauer, Kurk, De Breuck et al., to appear online in the journal Astronomy & Astrophysics on 15 October 2014.
APEX is a collaboration between the Max Planck Institute
for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO.
Operation of APEX at Chajnantor is entrusted to ESO.
The team is composed of H. Dannerbauer (University of Vienna,
Austria), J. D. Kurk (Max-Planck-Institut für extraterrestrische Physik,
Garching, Germany), C. De Breuck (ESO, Garching, Germany), D. Wylezalek
(ESO, Garching, Germany), J. S. Santos (INAF–Osservatorio Astrofisico
di Arcetri, Florence, Italy), Y. Koyama (National Astronomical
Observatory of Japan, Tokyo, Japan [NAOJ]; Institute of Space
Astronomical Science, Kanagawa, Japan), N. Seymour (International Centre
for Radio Astronomy Research, Curtin University, Perth, Australia), M.
Tanaka (NAOJ; Kavli Institute for the Physics and Mathematics of the
Universe, The University of Tokyo, Japan), N. Hatch (University of
Nottingham, United Kingdom), B. Altieri (Herschel Science Centre,
European Space Astronomy Centre, Villanueva de la Cañada, Spain [HSC]),
D. Coia (HSC), A. Galametz (INAF–Osservatorio di Roma, Italy), T. Kodama
(NAOJ), G. Miley (Leiden Observatory, the Netherlands), H. Röttgering
(Leiden Observatory), M. Sanchez-Portal (HSC), I. Valtchanov (HSC), B.
Venemans (Max-Planck Institut für Astronomie, Heidelberg, Germany) and
B. Ziegler (University of Vienna).
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
Contacts
Helmut Dannerbauer
University of Vienna
Vienna, Austria
Tel: +43 1 4277 53826
Email: helmut.dannerbauer@univie.ac.at
University of Vienna
Vienna, Austria
Tel: +43 1 4277 53826
Email: helmut.dannerbauer@univie.ac.at
Carlos De Breuck
ESO APEX Project Scientist
Garching bei München, Germany
Tel: +49 89 3200 6613
Email: cdebreuc@eso.org
ESO APEX Project Scientist
Garching bei München, Germany
Tel: +49 89 3200 6613
Email: cdebreuc@eso.org
Richard Hook
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
