ALMA witnesses assembly of galaxy in early Universe (annotated)
ALMA witnesses assembly of galaxy in early Universe
The Atacama Large
Millimeter/submillimeter Array (ALMA) has been used to detect the most
distant clouds of star-forming gas yet found in normal galaxies in the
early Universe. The new observations allow astronomers to start to see
how the first galaxies were built up and how they cleared the cosmic fog
during the era of reionisation. This is the first time that such
galaxies are seen as more than just faint blobs.
When the first galaxies started to form a few hundred million years
after the Big Bang, the Universe was full of a fog of hydrogen gas. But
as more and more brilliant sources — both stars and quasars powered by
huge black holes — started to shine they cleared away the mist and made
the Universe transparent to ultraviolet light [1].
Astronomers call this the epoch of reionisation, but little is known
about these first galaxies, and up to now they have just been seen as
very faint blobs. But now new observations using the power of ALMA are
starting to change this.
A team of astronomers led by Roberto Maiolino (Cavendish Laboratory and Kavli Institute for Cosmology, University of Cambridge, United Kingdom) trained ALMA on galaxies that were known to be seen only about 800 million years after the Big Bang [2]. The astronomers were not looking for the light from stars, but instead for the faint glow of ionised carbon [3]
coming from the clouds of gas from which the stars were forming. They
wanted to study the interaction between a young generation of stars and
the cold clumps that were assembling into these first galaxies.
They were also not looking for the extremely brilliant rare objects —
such as quasars and galaxies with very high rates of star formation —
that had been seen up to now. Instead they concentrated on rather less
dramatic, but much more common, galaxies that reionised the Universe and
went on to turn into the bulk of the galaxies that we see around us
now.
From one of the galaxies — given the label BDF 3299 — ALMA could pick
up a faint but clear signal from the glowing carbon. However, this glow
wasn’t coming from the centre of the galaxy, but rather from one side.
Co-author Andrea Ferrara (Scuola Normale Superiore, Pisa, Italy) explains the significance of the new findings: “This
is the most distant detection ever of this kind of emission from a
‘normal’ galaxy, seen less than one billion years after the Big Bang. It
gives us the opportunity to watch the build-up of the first galaxies.
For the first time we are seeing early galaxies not merely as tiny
blobs, but as objects with internal structure!”
The astronomers think that the off-centre location of the glow is
because the central clouds are being disrupted by the harsh environment
created by the newly formed stars — both their intense radiation and the
effects of supernova explosions — while the carbon glow is tracing
fresh cold gas that is being accreted from the intergalactic medium.
By combining the new ALMA observations with computer simulations, it
has been possible to understand in detail key processes occurring within
the first galaxies. The effects of the radiation from stars, the
survival of molecular clouds, the escape of ionising radiation and the
complex structure of the interstellar medium can now be calculated and
compared with observation. BDF 3299 is likely to be a typical example of
the galaxies responsible for reionisation.
“We have been trying to understand the interstellar medium and
the formation of the reionisation sources for many years. Finally to be
able to test predictions and hypotheses on real data from ALMA is an
exciting moment and opens up a new set of questions.This type of
observation will clarify many of the thorny problems we have with the
formation of the first stars and galaxies in the Universe,” adds Andrea Ferrara.
Roberto Maiolino concludes: “This study would have simply been
impossible without ALMA, as no other instrument could reach the
sensitivity and spatial resolution required. Although this is one of the
deepest ALMA observations so far it is still far from achieving its
ultimate capabilities. In future ALMA will image the fine structure of
primordial galaxies and trace in detail the build-up of the very first
galaxies.”
Notes
[1] Neutral hydrogen gas very efficiently absorbs all the high-energy
ultraviolet light emitted by young hot stars. Consequently, these stars
are almost impossible to observe in the early Universe. At the same
time, the absorbed ultraviolet light ionises the hydrogen, making it
fully transparent. The hot stars are therefore carving transparent
bubbles in the gas. Once all these bubbles merge to fill all of space,
reionisation is complete and the Universe becomes transparent.
[2] They had redshifts ranging from 6.8 to 7.1.
[3] Astronomers are particularly interested in ionised carbon as this particular spectral line carries away most of the energy injected by stars and allows astronomers to trace the cold gas out of which stars form. Specifically, the team were looking for the emission from singly ionised carbon (known as [C II]). This radiation is emitted at a wavelength of 158 micrometres, and by the time it is stretched by the expansion of the Universe arrives at ALMA at just the right wavelength for it to be detected at a wavelength of about 1.3 millimetres.
[2] They had redshifts ranging from 6.8 to 7.1.
[3] Astronomers are particularly interested in ionised carbon as this particular spectral line carries away most of the energy injected by stars and allows astronomers to trace the cold gas out of which stars form. Specifically, the team were looking for the emission from singly ionised carbon (known as [C II]). This radiation is emitted at a wavelength of 158 micrometres, and by the time it is stretched by the expansion of the Universe arrives at ALMA at just the right wavelength for it to be detected at a wavelength of about 1.3 millimetres.
More Information
This research was presented in a paper “The assembly of “normal” galaxies at z∼7 probed by ALMA”, by R. Maiolino et al., to appear in Monthly Notices of the Royal Astronomical Society on 22 July 2015.
The team is composed of R. Maiolino (Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom; Kavli Institute for Cosmology, University of Cambridge, Cambridge, United Kingdom) S. Carniani (Cavendish Laboratory; Kavli Institute for Cosmology; Universitá di Firenze, Florence, Italy), A. Fontana (INAF–Osservatorio Astronomico di Roma, Italy), L. Vallini (Scuola Normale Superiore, Pisa, Italy; Universitá di Bologna, Bologna, Italy), L. Pentericci (INAF–Osservatorio Astronomico di Roma, Italy), A. Ferrara (Scuola Normale Superiore, Pisa, Italy), E. Vanzella (INAF–Bologna Astronomical Observatory, Bologna, Italy), A. Grazian (INAF–Osservatorio Astronomico di Roma, Italy), S. Gallerani (Scuola Normale Superiore, Pisa, Italy), M. Castellano (INAF–Osservatorio Astronomico di Roma, Italy), S. Cristiani (INAF–Trieste Astronomical Observatory, Trieste, Italy), G. Brammer (Space Telescope Science Institute, Baltimore, Maryland, USA), P. Santini (INAF–Osservatorio Astronomico di Roma, Italy), J. Wagg (Square Kilometre Array Organization, Jodrell Bank Observatory, United Kingdom) and R. Williams (Cavendish Laboratory; Kavli Institute for Cosmology).
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the US National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. 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 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
Contact
Roberto Maiolino
Cavendish Laboratory & Kavli Institute for Cosmology, University of Cambridge
Cambridge, United Kingdom
Tel: +44 1223 761661
Cell: +44 7557 774718
Email: r.maiolino@mrao.cam.ac.uk
Andrea Ferrara
Scuola Normale Superiore
Pisa, Italy
Cell: +39 329 0715067
Email: andrea.ferrara@sns.it
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
This research was presented in a paper “The assembly of “normal” galaxies at z∼7 probed by ALMA”, by R. Maiolino et al., to appear in Monthly Notices of the Royal Astronomical Society on 22 July 2015.
The team is composed of R. Maiolino (Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom; Kavli Institute for Cosmology, University of Cambridge, Cambridge, United Kingdom) S. Carniani (Cavendish Laboratory; Kavli Institute for Cosmology; Universitá di Firenze, Florence, Italy), A. Fontana (INAF–Osservatorio Astronomico di Roma, Italy), L. Vallini (Scuola Normale Superiore, Pisa, Italy; Universitá di Bologna, Bologna, Italy), L. Pentericci (INAF–Osservatorio Astronomico di Roma, Italy), A. Ferrara (Scuola Normale Superiore, Pisa, Italy), E. Vanzella (INAF–Bologna Astronomical Observatory, Bologna, Italy), A. Grazian (INAF–Osservatorio Astronomico di Roma, Italy), S. Gallerani (Scuola Normale Superiore, Pisa, Italy), M. Castellano (INAF–Osservatorio Astronomico di Roma, Italy), S. Cristiani (INAF–Trieste Astronomical Observatory, Trieste, Italy), G. Brammer (Space Telescope Science Institute, Baltimore, Maryland, USA), P. Santini (INAF–Osservatorio Astronomico di Roma, Italy), J. Wagg (Square Kilometre Array Organization, Jodrell Bank Observatory, United Kingdom) and R. Williams (Cavendish Laboratory; Kavli Institute for Cosmology).
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the US National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. 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 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
Contact
Roberto Maiolino
Cavendish Laboratory & Kavli Institute for Cosmology, University of Cambridge
Cambridge, United Kingdom
Tel: +44 1223 761661
Cell: +44 7557 774718
Email: r.maiolino@mrao.cam.ac.uk
Andrea Ferrara
Scuola Normale Superiore
Pisa, Italy
Cell: +39 329 0715067
Email: andrea.ferrara@sns.it
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
