Surprisingly mature galaxies in the early Universe
IMAGE: ARTIST'S ILLUSTRATION OF A DUSTY, ROTATING DISTANT GALAXY, IN THE EARLY UNIVERSE. IN THIS IMAGE, THE RED COLOR REPRESENTS GAS, AND BLUE/BROWN REPRESENTS DUST AS SEEN IN RADIO WAVES WITH... view more
CREDIT: © B. SAXTON NRAO/AUI/NSF, ESO, NASA/STSCI; NAOJ/SUBARU
When the Universe was only a tenth of its current age its galaxies experienced a growth spurt. It was this period that the scientists in the ALPINE project (1) focused on when they used ESO's ALMA (2) telescope to carry out the first ever large survey of distant galaxies. To their surprise, these galaxies observed in the early stages of their life were far more mature than expected. Their work is the subject of a series of articles published on 27 October 2020 in the journal Astronomy & Astrophysics, signed among others by members of the CNRS and Aix-Marseille Université (3).
Galaxies began to form very early in the history of the Universe. To study their infancy, it is therefore necessary to go back to the dawn of time, by observing very distant galaxies. The ALPINE project focused on a period between 1 and 1.5 billion years after the Big Bang, when the first galaxies experienced a phase of rapid growth. Although such distant galaxies have already been observed, this is the first time that so many of them have been studied systematically. Images of 118 massive (4) galaxies, obtained with the Hubble (visible light) and Spitzer (near infrared) space telescopes, as well as spectra acquired using the ground-based VLT and Keck telescopes, were supplemented by 70 hours of observation with ALMA at submillimetre wavelengths (between the infrared and radio waves).
ALMA can quantify dust, a sign of maturity in galaxies, and cold gas, which provides information about their rate of growth and the number of stars they can form, as well as the motion of this gas, thus revealing the dynamics of galaxies. And this turned up some surprising data. For a start, the observed galaxies proved to be very rich not only in cold gas, which fuels star formation, but also in dust, which is thought to be a by-product of stars at the end of their lives. So despite their young age, these galaxies had apparently seen the formation and death of a first generation of stars! The galaxies surveyed also exhibit an astonishing diversity of shapes: some are disordered, others already have a rotating disc that may end up as a spiral structure like the Milky Way, while yet others have been spotted in the process of merging. Another surprising observation is that certain galaxies appear to be ejecting gas, forming mysterious haloes around them. The survey thus raises a number of new questions about the early evolution of galaxies.
CAPTION
Mosaic showing some of the galaxies observed by ALMA. The bright yellow regions are those where the most stars are forming (the ionised carbon (C+) line makes it possible to see the formation of stars obscured by dust). The second image from the left in the top row shows a triple merger.
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To find out more, read NRAO's news release:
https:/
Notes:
(1) Acronym for the ALMA Large Program to INvestigate C+ at Early times
(2) ALMA (Atacama Large Millimeter/submillimeter Array) is a telescope designed for the study of radiation from the coldest objects in the Universe, and consists of 66 antennas located in the Atacama desert in the Chilean Andes.
(3) from the Laboratoire d'Astrophysique de Marseille (CNRS/Aix-Marseille Université/CNES) and the Institut de Recherche en Astrophysique et Planétologie (CNRS/Université Toulouse III - Paul Sabatier/ CNES).
(4) They have already reached a mass similar to that of the Milky Way today.
Galaxies in the infant universe were surprisingly mature
ALMA telescope conducts largest survey yet of distant galaxies in the early universe
VIDEO: BRIEF VIDEO EXPLAINING THIS RESEARCH RESULT. view more
CREDIT: B. SAXTON NRAO/AUI/NSF
Massive galaxies were already much more mature in the early universe than previously expected. This was shown by an international team of astronomers who studied 118 distant galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA).
Most galaxies formed when the universe was still very young. Our own galaxy, for example, likely started forming 13.6 billion years ago, in our 13.8 billion-year-old universe. When the universe was only ten percent of its current age (1-1.5 billion years after the Big Bang), most of the galaxies experienced a "growth spurt". During this time, they built up most of their stellar mass and other properties, such as dust, heavy element content, and spiral-disk shapes, that we see in today's galaxies. Therefore, if we want to learn how galaxies like our Milky Way formed, it is important to study this epoch.
In a survey called ALPINE (the ALMA Large Program to Investigate C+ at Early Times), an international team of astronomers studied 118 galaxies experiencing such a "growth spurt" in the early universe. "To our surprise, many of them were much more mature than we had expected," said Andreas Faisst of the Infrared Processing and Analysis Center (IPAC) at the California Institute of Technology (Caltech).
Galaxies are considered more "mature" than "primordial" when they contain a significant amount of dust and heavy elements. "We didn't expect to see so much dust and heavy elements in these distant galaxies," said Faisst. Dust and heavy elements (defined by astronomers as all elements heavier than hydrogen and helium) are considered to be a by-product of dying stars. But galaxies in the early universe have not had much time to build stars yet, so astronomers don't expect to see much dust or heavy elements there either.
"From previous studies, we understood that such young galaxies are dust-poor," said Daniel Schaerer of the University of Geneva in Switzerland. "However, we find around 20 percent of the galaxies that assembled during this early epoch are already very dusty and a significant fraction of the ultraviolet light from newborn stars is already hidden by this dust," he added.
Many of the galaxies were also considered to be relatively grown-up because they showed a diversity in their structures, including the first signs of rotationally supported disks - which may later lead to galaxies with a spiral structure as is observed in galaxies such as our Milky Way. Astronomers generally expect that galaxies in the early universe look like train wrecks because they often collide. "We see many galaxies that are colliding, but we also see a number of them rotating in an orderly fashion with no signs of collisions," said John Silverman of the Kavli Institute for the Physics and Mathematics of the Universe in Japan.
ALMA has spotted very distant galaxies before, such as MAMBO-9 (a very dusty galaxy) and the Wolfe Disk (a galaxy with a rotating disk). But it was hard to say whether these discoveries were unique, or whether there were more galaxies like them out there. ALPINE is the first survey that enabled astronomers to study a significant number of galaxies in the early universe, and it shows that they might evolve faster than expected. But the scientists don't yet understand how these galaxies grew up so fast, and why some of them already have rotating disks.
Observations from ALMA were crucial for this research because the radio telescope can see the star formation that is hidden by dust and trace the motion of gas emitted from star-forming regions. Surveys of galaxies in the early universe commonly use optical and infrared telescopes. These allow the measurement of the unobscured star formation and stellar masses. However, these telescopes have difficulties measuring dust obscured regions, where stars form, or the motions of gas in these galaxies. And sometimes they don't see a galaxy at all. "With ALMA we discovered a few distant galaxies for the first time. We call these Hubble-dark as they could not be detected even with the Hubble telescope," said Lin Yan of Caltech.
To learn more about distant galaxies, the astronomers want to point ALMA at individual galaxies for a longer time. "We want to see exactly where the dust is and how the gas moves around. We also want to compare the dusty galaxies to others at the same distance and figure out if there might be something special about their environments," added Paolo Cassata of the University of Padua in Italy, formerly at the Universidad de Valparaíso in Chile.
ALPINE is the first and largest multi-wavelength survey of galaxies in the early universe. For a large sample of galaxies the team collected measurements in the optical (including Subaru, VISTA, Hubble, Keck and VLT), infrared (Spitzer), and radio (ALMA). Multi-wavelength studies are needed to get the full picture of how galaxies are built up. "Such a large and complex survey is only possible thanks to the collaboration between multiple institutes across the globe," said Matthieu Béthermin of the Laboratoire d'Astrophysique de Marseille in France.
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The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
Media contact:
Iris Nijman
NRAO News and Public Information Manager
inijman@nrao.edu
A list of ALPINE publications to date can be found here: http://alpine.
All ALPINE papers are dedicated to the memory of Olivier Le Fèvre, Principal Investigator of ALPINE.
Co-Principal Investigators of ALPINE are:
- Andreas Faisst, Caltech/IPAC, USA
- Lin Yan, Caltech, USA
- Peter Capak, Caltech/IPAC, USA
- John Silverman, Kavli Institute for the Physics and Mathematics of the Universe, Japan
- Matthieu Béthermin, Laboratoire d'Astrophysique de Marseille, France
- Paolo Cassata, University of Padua, Italy
- Daniel Schaerer, University of Geneva, Switzerland
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (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 Ministry of Science and Technology (MOST) 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.
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