Galaxy mergers could limit star formation
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VIDEO: A SIMULATED COLLISION BETWEEN TWO GAS-RICH GALAXIES. PART OF THE GAS IS EJECTED IN LARGE TAILS AND AS THE GALAXIES GET CLOSER THEY MERGE TO FORM A SINGLE SYSTEM. view more
CREDIT: JEREMY FENSCH, ET AL
Astronomers have looked nine billion years into the past to find evidence that galaxy mergers in the early universe could shut down star formation and affect galaxy growth.
New research led by Durham University, UK, the French Alternative Energies and Atomic Energy Commission (CEA)-Saclay and the University of Paris-Saclay, shows that a huge amount of star-forming gas was ejected into the intergalactic medium by the coming together of two galaxies.
The researchers say that this event, together with a large amount of star formation in the nuclear regions of the galaxy, would eventually deprive the merged galaxy - called ID2299 - of fuel for new stars. This would stop star formation for several hundred million years, effectively halting the galaxy's development.
Astronomers observe many massive, dead galaxies containing very old stars in the nearby Universe and don't exactly know how these galaxies have been formed.
Simulations suggest that winds generated by active black holes as they feed, or those created by intense star formation, are responsible for such deaths by expelling the gas from galaxies.
Now the Durham-led study offers galaxy mergers as another way of shutting down star formation and altering galaxy growth.
CAPTION
This artist's impression of ID2299 shows the galaxy, the product of a galactic collision, and some of its gas being ejected by a "tidal tail" as a result of the merger. New observations made with ALMA, in which ESO is a partner, have captured the earliest stages of this ejection, before the gas reached the very large scales depicted in this artist's impression.
CREDIT
ESO/M. Kornmesser
Observational features of winds and "tidal tails" caused by the gravitational interaction between galaxies in such mergers can be very similar, so the researchers suggest that some past results where galactic winds have been seen as the cause of halting star formation might need to be re-evaluated.
The findings are published in the journal Nature Astronomy.
Lead author Dr Annagrazia Puglisi, in Durham University's Centre for Extragalactic Astronomy, said: "We don't yet know what the exact processes are behind the switching off of star formation in massive galaxies.
"Feedback driven winds from star formation or active black holes are thought to be the main responsible for expelling the gas and quenching the growth of massive galaxies.
"Our research provides compelling evidence that the gas being flung from ID2299 is likely to have been tidally ejected because of the merger between two gas rich spiral galaxies. The gravitational interaction between two galaxies can thus provide sufficient angular momentum to kick out part of the gas into the galaxy surroundings.
"This suggests that mergers are also capable of altering the future evolution of a galaxy by limiting its ability to form stars over millions of years and deserve more investigation when thinking about the factors that limit galaxy growth."
Due to the amount of time it takes the light from ID2299 to reach Earth the researchers were able to see the galaxy as it would have appeared nine billion years ago when it was in the late stages of its merger.
This is a time when the universe was only 4.5 billion years old and was in its most active, "young adult" phase if compared to a human life.
Using the European Southern Observatory's Atacama Large Millimeter Array (ALMA) telescope, in northern Chile, the researchers saw it was ejecting about half of its total gas reservoir into the galaxy surroundings.
Researchers were able to rule out star formation and the galaxy's active black hole as the reason for this ejection by comparing their measurements to previous studies and simulations and by measuring the physical properties of the escaped gas.
The rate at which the gas is being expelled from ID2299 is too high to have been caused by the energy created by a black hole or starburst as seen in previous studies, while simulations suggest that no black holes can kick out as much cold gas from a galaxy.
The excitation of the escaped gas is also not compatible with a wind generated by a black hole or the birth of new stars.
Co-author Dr Emanuele Daddi, from CEA-Saclay said: "This galaxy is witnessing a truly extreme event.
"It is probably caught during an important physical phase for galaxy evolution that occurs within a relatively short time window. We had to look at over 100 galaxies with ALMA to find it."
Fellow co-author Dr Jeremy Fensch, of the Centre de Recherche Astrophysique de Lyon, added: "Studying this single case unveiled the possibility that this type of event might not be unusual at all and that many galaxies suffered from this 'gravitational gas removal', including misinterpreted past observations.
"This might have huge consequences on our understanding of what actually shapes the evolution of galaxies."
CAPTION
Map of the cold molecular gas from the galaxy ID2299 taken using the European Southern Observatory's Atacama Large Millimeter Array (ALMA) telescope.
CREDIT
A Puglisi et al
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The researchers now hope to obtain higher resolution images of ID2299 and other distant galaxy mergers and carry out computer simulations to further understand the effect galaxy mergers have on the life cycle of galaxies.
The research was funded by the Science and Technology Facilities Council, part of UK Research and Innovation, Region Île-de-France, and the CEA-Enhanced Eurotalents program, co-funded by the FP7 Marie-Sk?odowska-Curie COFUND program, Comunidad de Madrid, Spanish Ministry of Science, Innovation and Universities (MICIU), and co-financed by FEDER (European Regional Development Funds).
ALMA captures distant colliding galaxy dying out as it loses the ability to form stars
IMAGE: THIS ARTIST'S IMPRESSION OF ID2299 SHOWS THE GALAXY, THE PRODUCT OF A GALACTIC COLLISION, AND SOME OF ITS GAS BEING EJECTED BY A "TIDAL TAIL " AS A RESULT OF THE... view more
CREDIT: ESO/M. KORNMESSER
Galaxies begin to "die" when they stop forming stars, but until now astronomers had never clearly glimpsed the start of this process in a far-away galaxy. Using the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, astronomers have seen a galaxy ejecting nearly half of its star-forming gas. This ejection is happening at a startling rate, equivalent to 10 000 Suns-worth of gas a year -- the galaxy is rapidly losing its fuel to make new stars. The team believes that this spectacular event was triggered by a collision with another galaxy, which could lead astronomers to rethink how galaxies stop bringing new stars to life.
"This is the first time we have observed a typical massive star-forming galaxy in the distant Universe about to 'die' because of a massive cold gas ejection," says Annagrazia Puglisi, lead researcher on the new study, from the Durham University, UK, and the Saclay Nuclear Research Centre (CEA-Saclay), France. The galaxy, ID2299, is distant enough that its light takes some 9 billion years to reach us; we see it when the Universe was just 4.5 billion years old.
The gas ejection is happening at a rate equivalent to 10 000 Suns per year, and is removing an astonishing 46% of the total cold gas from ID2299. Because the galaxy is also forming stars very rapidly, hundreds of times faster than our Milky Way, the remaining gas will be quickly consumed, shutting down ID2299 in just a few tens of million years.
The event responsible for the spectacular gas loss, the team believes, is a collision between two galaxies, which eventually merged to form ID2299. The elusive clue that pointed the scientists towards this scenario was the association of the ejected gas with a "tidal tail". Tidal tails are elongated streams of stars and gas extending into interstellar space that result when two galaxies merge, and they are usually too faint to see in distant galaxies. However, the team managed to observe the relatively bright feature just as it was launching into space, and were able to identify it as a tidal tail.
Most astronomers believe that winds caused by star formation and the activity of black holes at the centres of massive galaxies are responsible for launching star-forming material into space, thus ending galaxies' ability to make new stars. However, the new study published today in Nature Astronomy suggests that galactic mergers can also be responsible for ejecting star-forming fuel into space.
"Our study suggests that gas ejections can be produced by mergers and that winds and tidal tails can appear very similar," says study co-author Emanuele Daddi of CEA-Saclay. Because of this, some of the teams that previously identified winds from distant galaxies could in fact have been observing tidal tails ejecting gas from them. "This might lead us to revise our understanding of how galaxies 'die'," Daddi adds.
Puglisi agrees about the significance of the team's finding, saying: "I was thrilled to discover such an exceptional galaxy! I was eager to learn more about this weird object because I was convinced that there was some important lesson to be learned about how distant galaxies evolve."
This surprising discovery was made by chance, while the team were inspecting a survey of galaxies made with ALMA (https:/
"ALMA has shed new light on the mechanisms that can halt the formation of stars in distant galaxies. Witnessing such a massive disruption event adds an important piece to the complex puzzle of galaxy evolution," says Chiara Circosta, a researcher at the University College London, UK, who also contributed to the research.
In the future, the team could use ALMA to make higher-resolution and deeper observations of this galaxy, enabling them to better understand the dynamics of the ejected gas. Observations with the future ESO's Extremely Large Telescope could allow the team to explore the connections between the stars and gas in ID2299, shedding new light on how galaxies evolve.
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More information
This research was presented in the paper "A titanic interstellar medium ejection from a massive starburst galaxy at z=1.4" to appear in Nature Astronomy (doi: 10.1038/s41550-020-01268-x).
The team is composed of A. Puglisi (Centre for Extragalactic Astronomy, Durham University, UK and CEA, IRFU, DAp, AIM, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, CNRS, France [CEA]), E. Daddi (CEA), M. Brusa (Dipartimento di Fisica e Astronomia, Università di Bologna, Italy and INAF-Osservatorio Astronomico di Bologna, Italy), F. Bournaud (CEA), J. Fensch (Univ. Lyon, ENS de Lyon, Univ. Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon, France), D. Liu (Max Planck Institute for Astronomy, Germany), I. Delvecchio (CEA), A. Calabrò (INAF-Osservatorio Astronomico di Roma, Italy), C. Circosta (Department of Physics & Astronomy, University College London, UK), F. Valentino (Cosmic Dawn Center at the Niels Bohr Institute, University of Copenhagen and DTU-Space, Technical University of Denmark, Denmark), M. Perna (Centro de Astrobiología (CAB, CSIC-INTA), Departamento de Astrofísica, Spain and INAF-Osservatorio Astrofisico di Arcetri, Italy), S. Jin (Instituto de Astrofísica de Canarias and Universidad de La Laguna, Dpto. Astrofísica, Spain), A. Enia (Dipartimento di Fisica e Astronomia, Università di Padova, Italy [Padova]), C. Mancini (Padova) and G. Rodighiero (Padova and INAF-Osservatorio Astronomico di Padova, Italy).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world's most productive ground-based astronomical observatory by far. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. 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 and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world's largest and most sensitive gamma-ray observatory. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become "the world's biggest eye on the sky".
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 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.
Links
- Research paper - https:/
/ www. eso. org/ public/ archives/ releases/ sciencepapers/ eso2101/ eso2101a. pdf - Photos of ALMA - https:/
/ www. eso. org/ public/ images/ archive/ category/ alma/ - For scientists: got a story? Pitch your research - http://eso.
org/ sci/ publications/ announcements/ sciann17277. html
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