ALMA and Hubble Space Telescope views of the distant dusty galaxy A2744_YD4
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Most distant object ever observed by ALMA
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Artist’s impression of dust formation by supernovae in A2744_YD4
Zooming in on the young dusty galaxy A2744_YD4
Most distant object ever observed by ALMA
Astronomers have used ALMA to detect a
huge mass of glowing stardust in a galaxy seen when the Universe was
only four percent of its present age. This galaxy was observed shortly
after its formation and is the most distant galaxy in which dust has
been detected. This observation is also the most distant detection of
oxygen in the Universe. These new results provide brand-new insights
into the birth and explosive deaths of the very first stars.
An international team of astronomers, led by Nicolas Laporte of University College London, have used the Atacama Large Millimeter/submillimeter Array
(ALMA) to observe A2744_YD4, the youngest and most remote galaxy ever
seen by ALMA. They were surprised to find that this youthful galaxy
contained an abundance of interstellar dust — dust formed by the deaths
of an earlier generation of stars.
Follow-up observations using the X-shooter instrument on ESO’s Very Large Telescope
confirmed the enormous distance to A2744_YD4. The galaxy appears to us
as it was when the Universe was only 600 million years old, during the
period when the first stars and galaxies were forming [1].
“Not only is A2744_YD4 the most distant galaxy yet observed by ALMA,” comments Nicolas Laporte, “but the detection of so much dust indicates early supernovae must have already polluted this galaxy.”
Cosmic dust is mainly composed of silicon, carbon and
aluminium, in grains as small as a millionth of a centimetre across. The
chemical elements in these grains are forged inside stars and are
scattered across the cosmos when the stars die, most spectacularly in
supernova explosions, the final fate of short-lived, massive stars.
Today, this dust is plentiful and is a key building block in the
formation of stars, planets and complex molecules; but in the early
Universe — before the first generations of stars died out — it was
scarce.
The observations of the dusty galaxy A2744_YD4 were made
possible because this galaxy lies behind a massive galaxy cluster called
Abell 2744 [2]. Because of a phenomenon called gravitational lensing,
the cluster acted like a giant cosmic “telescope” to magnify the more
distant A2744_YD4 by about 1.8 times, allowing the team to peer far back
into the early Universe.
The ALMA observations also detected the glowing emission of
ionised oxygen from A2744_YD4. This is the most distant, and hence
earliest, detection of oxygen in the Universe, surpassing another ALMA result from 2016.
The detection of dust in the early Universe provides new
information on when the first supernovae exploded and hence the time
when the first hot stars bathed the Universe in light. Determining the
timing of this “cosmic dawn” is one of the holy grails of modern
astronomy, and it can be indirectly probed through the study of early
interstellar dust.
The team estimates that A2744_YD4 contained an amount of
dust equivalent to 6 million times the mass of our Sun, while the
galaxy’s total stellar mass — the mass of all its stars — was 2 billion
times the mass of our Sun. The team also measured the rate of star
formation in A2744_YD4 and found that stars are forming at a rate of 20
solar masses per year — compared to just one solar mass per year in the
Milky Way [3].
“This rate is not unusual for such a distant galaxy, but it does shed light on how quickly the dust in A2744_YD4 formed,” explains Richard Ellis (ESO and University College London), a co-author of the study. “Remarkably, the required time is only about 200 million years — so we are witnessing this galaxy shortly after its formation.”
This means that significant star formation began
approximately 200 million years before the epoch at which the galaxy is
being observed. This provides a great opportunity for ALMA to help study
the era when the first stars and galaxies “switched on” — the earliest
epoch yet probed. Our Sun, our planet and our existence are the products
— 13 billion years later — of this first generation of stars. By
studying their formation, lives and deaths, we are exploring our
origins.
“With ALMA, the prospects for performing deeper and
more extensive observations of similar galaxies at these early times are
very promising,” says Ellis.
And Laporte concludes: “Further measurements of this
kind offer the exciting prospect of tracing early star formation and the
creation of the heavier chemical elements even further back into the
early Universe.”
Notes
[1] This time corresponds to a redshift of z=8.38, during the epoch of reionisation.
[3] This rate means that the total mass of the stars formed every year is equivalent to 20 times the mass of the Sun.
Notes
[1] This time corresponds to a redshift of z=8.38, during the epoch of reionisation.
[2] Abell 2744 is a massive
object, lying 3.5 billion light-years away (redshift 0.308), that is
thought to be the result of four smaller galaxy clusters colliding. It
has been nicknamed Pandora’s Cluster because of the many strange and
different phenomena that were unleashed by the huge collision that
occurred over a period of about 350 million years. The galaxies only
make up five percent of the cluster’s mass, while dark matter makes up
seventy-five percent, providing the massive gravitational influence
necessary to bend and magnify the light of background galaxies. The
remaining twenty percent of the total mass is thought to be in the form
of hot gas.
More information
This research was presented in a paper entitled “Dust in
the Reionization Era: ALMA Observations of a z =8.38
Gravitationally-Lensed Galaxy” by Laporte et al., to appear in The Astrophysical Journal Letters.
The team is composed of N. Laporte (University College
London, UK), R. S. Ellis (University College London, UK; ESO, Garching,
Germany), F. Boone (Institut de Recherche en Astrophysique et
Planétologie (IRAP), Toulouse, France), F. E. Bauer (Pontificia
Universidad Católica de Chile, Instituto de Astrofísica, Santiago,
Chile), D. Quénard (Queen Mary University of London, London, UK), G.
Roberts-Borsani (University College London, UK), R. Pelló (Institut de
Recherche en Astrophysique et Planétologie (IRAP), Toulouse, France), I.
Pérez-Fournon (Instituto de Astrofísica de Canarias, Tenerife, Spain;
Universidad de La Laguna, Tenerife, Spain), and A. Streblyanska
(Instituto de Astrofísica de Canarias, Tenerife, Spain; Universidad de
La Laguna, Tenerife, Spain).
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of ESO, the U.S.
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
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ESO carries out an ambitious programme focused on the design,
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enabling astronomers to make important scientific discoveries. ESO also
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operates the Very Large Telescope, the world’s most advanced
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ALMA, the largest astronomical project in existence. And on Cerro
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Extremely Large Telescope, the E-ELT, which will become “the world’s
biggest eye on the sky”.
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Contacts
Nicolas Laporte
University College London
United Kingdom
Tel: +44 2 035 495 802
Cell: +44 7452 807 591
Email: n.laporte@ucl.ac.uk
Richard Ellis
ESO
Garching bei München, Germany
Tel: +44 7885 403334
Cell: +49 151 629 56829
Email: rellis@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
Source: ESO
