The starburst galaxy NGC 253 seen with the VISTA and ALMA
The galaxy NGC 253 in the constellation of Sculptor
Wide-field view of NGC 253 from the VLT Survey Telescope
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ALMA Sheds Light on Mystery of Missing Massive Galaxies
New observations from the ALMA telescope
in Chile have given astronomers the best view yet of how vigorous star
formation can blast gas out of a galaxy and starve future generations of
stars of the fuel they need to form and grow. The dramatic images show
enormous outflows of molecular gas ejected by star-forming regions in
the nearby Sculptor Galaxy. These new results help to explain the
strange paucity of very massive galaxies in the Universe. The study is
published in the journal Nature on 25 July 2013.
Galaxies — systems like our own Milky Way that contain up to hundreds
of billions of stars — are the basic building blocks of the cosmos. One
ambitious goal of contemporary astronomy is to understand the ways in
which galaxies grow and evolve, a key question being star formation:
what determines the number of new stars that will form in a galaxy?
The Sculptor Galaxy, also known as NGC 253, is a spiral galaxy
located in the southern constellation of Sculptor. At a distance of
around 11.5 million light-years from our Solar System it is one of our
closer intergalactic neighbours, and one of the closest starburst
galaxies [1] visible from the southern hemisphere.
Using the Atacama Large Millimeter/submillimeter Array (ALMA) astronomers have discovered billowing columns of cold, dense gas fleeing from the centre of the galactic disc.
“With ALMA’s superb resolution and sensitivity, we can clearly
see for the first time massive concentrations of cold gas being
jettisoned by expanding shells of intense pressure created by young
stars,” said Alberto Bolatto of the University of Maryland, USA lead author of the paper. “The
amount of gas we measure gives us very good evidence that some growing
galaxies spew out more gas than they take in. We may be seeing a
present-day example of a very common occurrence in the early Universe.”
These results may help to explain why astronomers have found
surprisingly few high-mass galaxies throughout the cosmos. Computer
models show that older, redder galaxies should have considerably more
mass and a larger number of stars than we currently observe. It seems
that the galactic winds or outflow of gas are so strong that they
deprive the galaxy of the fuel for the formation of the next generation
of stars [2].
“These features trace an arc that is almost perfectly aligned with the edges of the previously observed hot, ionised gas outflow,”
noted Fabian Walter, a lead investigator at the Max Planck Institute
for Astronomy in Heidelberg, Germany, and a co-author of the paper. “We can now see the step-by-step progression of starburst to outflow.”
The researchers determined that vast quantities of molecular gas —
nearly ten times the mass of our Sun each year and possibly much more —
were being ejected from the galaxy at velocities between 150 000 and
almost 1 000 000 kilometres per hour [3].
The total amount of gas ejected would add up to more gas than actually
went into forming the galaxy’s stars in the same time. At this rate, the
galaxy could run out of gas in as few as 60 million years.
“For me, this is a prime example of how new instruments
shape the future of astronomy. We have been studying the starburst
region of NGC 253 and other nearby starburst galaxies for almost ten
years. But before ALMA, we had no chance to see such details,” says Walter. The study used an early configuration of ALMA with only 16 antennas. “It’s exciting to think what the complete ALMA with 66 antennas will show for this kind of outflow!” Walter adds.
More studies with the full ALMA array will help determine the
ultimate fate of the gas carried away by the wind, which will reveal
whether the starburst-driven winds are recycling or truly removing star
forming material.
Notes
[1] Starburst galaxies are producing
stars at an exceptionally high rate. As NGC 253 is one of the closest
such extreme objects it is an ideal target to study the effect of such
growth frenzy on the galaxy hosting it.
[2] Previous observations had shown hotter, but much
less dense, gas streaming away from NGC 253’s star-forming regions, but
alone this would have little, if any, impact on the fate of the galaxy
and its ability to form future generations of stars. This new ALMA data
show the much more dense molecular gas getting its initial “kick” from
the formation of new stars and then being swept along with the thin, hot
gas on its way to the galactic halo.
[3] Although the velocities are high, they may not be
high enough for the gas to be ejected from the galaxy. It would get
trapped in the galactic halo for many millions of years, and could
eventually rain back on the disk, causing new episodes of star
formation.
More information
This research was presented in a paper “The
Starburst-Driven Molecular Wind in NGC 253 and the Suppression of Star
Formation”, by Alberto D. Bolatto et al., to appear in Nature on 25 July 2013.
The team is composed of A. D. Bolatto (Department of Astronomy,
Laboratory for Millimeter-wave Astronomy, and Joint Space Institute,
University of Maryland, USA), S. R. Warren (University of Maryland), A.
K. Leroy (National Radio Astronomy Observatory, Charlottesville, USA),
F. Walter (Max-Planck Institut für Astronomie, Heidelberg, Germany), S.
Veilleux (University of Maryland), E. C. Ostriker (Department of
Astrophysical Sciences, Princeton University, USA), J. Ott (National
Radio Astronomy Observatory, New Mexico, USA), M. Zwaan (European
Southern Observatory, Garching, Germany), D. B. Fisher (University of
Maryland), A. Weiss (Max-Planck-Institut für Radioastronomie, Bonn,
Germany), E. Rosolowsky (Department of Physics, University of Alberta,
Canada) and J. Hodge (Max-Planck Institut für Astronomie, Heidelberg,
Germany).
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
Alberto BolattoUniversity of Maryland
USA
Tel: +49 6221 528 493
Email: bolatto@astro.umd.edu
Martin Zwaan
ESO
Garching bei München, Germany
Tel: +49 89 3200 6834
Email: mzwaan@eso.org
Fabian Walter
Max-Planck Institut für Astronomie
Heidelberg, Germany
Tel: +49 6221 528 225
Email: walter@mpia.de
Richard Hook
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
