Hubble finds early, massive galaxies running on empty
IMAGE: THESE IMAGES ARE COMPOSITES FROM NASA'S HUBBLE SPACE TELESCOPE AND THE ATACAMA LARGE MILLIMETER/SUBMILLIMETER ARRAY (ALMA). THE BOXED AND PULLOUT IMAGES SHOW TWO OF THE SIX, DISTANT, MASSIVE GALAXIES WHERE SCIENTISTS FOUND STAR FORMATION HAS CEASED DUE TO THE DEPLETION OF A FUEL SOURCE – COLD HYDROGEN GAS. HUBBLE, TOGETHER WITH ALMA, FOUND THESE ODD GALAXIES WHEN THEY COMBINED FORCES WITH THE "NATURAL LENS" IN SPACE CREATED BY FOREGROUND MASSIVE GALAXY CLUSTERS. THE CLUSTERS' GRAVITY STRETCHES AND AMPLIFIES THE LIGHT OF THE BACKGROUND GALAXIES IN AN EFFECT CALLED GRAVITATIONAL LENSING. THIS PHENOMENON ALLOWS ASTRONOMERS TO USE MASSIVE GALAXY CLUSTERS AS NATURAL MAGNIFYING GLASSES TO STUDY DETAILS IN THE DISTANT GALAXIES THAT WOULD OTHERWISE BE IMPOSSIBLE TO SEE. THE YELLOW TRACES THE GLOW OF STARLIGHT. THE ARTIFICIAL PURPLE COLOR TRACES COLD DUST FROM ALMA OBSERVATIONS. THIS COLD DUST IS USED AS A PROXY FOR THE COLD HYDROGEN GAS NEEDED FOR STAR FORMATION. EVEN WITH ALMA'S SENSITIVITY, SCIENTISTS DO NOT DETECT DUST IN MOST OF THE SIX GALAXIES SAMPLED. ONE EXAMPLE IS MRG-M1341, AT UPPER RIGHT. IT LOOKS DISTORTED BY THE "FUNHOUSE MIRROR" OPTICAL EFFECTS OF LENSING. IN CONTRAST, THE PURPLE BLOB TO THE LEFT OF THE GALAXY IS AN EXAMPLE OF A DUST-AND-GAS-RICH GALAXY. ONE EXAMPLE OF THE DETECTION OF COLD DUST ALMA DID MAKE IS GALAXY MRG-M2129 AT BOTTOM RIGHT. THE GALAXY ONLY HAS DUST AND GAS IN THE VERY CENTER. THIS SUGGESTS THAT STAR FORMATION MAY HAVE SHUT DOWN FROM THE OUTSKIRTS INWARD. ANNOTATED IMAGE ON THE LEFT, UNANNOTATED IMAGE ON THE RIGHT. view more
CREDIT: CREDITS: IMAGE PROCESSING: JOSEPH DEPASQUALE (STSCI)
When the universe was about 3 billion years old, just 20% of its current age, it experienced the most prolific period of star birth in its history. But when NASA's Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile gazed toward cosmic objects in this period, they found something odd: six early, massive, "dead" galaxies that had run out of the cold hydrogen gas needed to make stars.
Without more fuel for star formation, these galaxies were literally running on empty. The findings are published in the journal Nature.
"At this point in our universe, all galaxies should be forming lots of stars. It's the peak epoch of star formation," explained lead author Kate Whitaker, assistant professor of astronomy at the University of Massachusetts, Amherst. Whitaker is also associate faculty at the Cosmic Dawn Center in Copenhagen, Denmark. "So what happened to all the cold gas in these galaxies so early on?"
This study is a classic example of the harmony between Hubble and ALMA observations. Hubble pinpointed where in the galaxies the stars exist, showing where they formed in the past. By detecting the cold dust that serves as a proxy for the cold hydrogen gas, ALMA showed astronomers where stars could form in the future if enough fuel were present.
Using Nature's Own Telescopes
The study of these early, distant, dead galaxies was part of the appropriately named REQUIEM program, which stands for Resolving QUIEscent Magnified Galaxies At High Redshift. (Redshift happens when light is stretched by the expansion of space and appears shifted toward the red part of the spectrum. The farther away a galaxy is with respect to the observer, the redder it appears.)
The REQUIEM team uses extremely massive foreground galaxy clusters as natural telescopes. The immense gravity of a galaxy cluster warps space, bending and magnifying light from background objects. When an early, massive, and very distant galaxy is positioned behind such a cluster, it appears greatly stretched and magnified, allowing astronomers to study details that would otherwise be impossible to see. This is called "strong gravitational lensing."
Only by combining the exquisite resolution of Hubble and ALMA with this strong lensing was the REQUIEM team able to able to understand the formation of these six galaxies, which appear as they did only a few billion years after the big bang.
"By using strong gravitational lensing as a natural telescope, we can find the distant, most massive, and first galaxies to shut down their star formation," said Whitaker. "I like to think about it like doing science of the 2030s or 40s – with powerful next-generation space telescopes – but today instead by combining the capabilities of Hubble and ALMA, which are boosted by strong lensing."
"REQUIEM pulled together the largest sample to date of these rare, strong-lensed, dead galaxies in the early universe, and strong lensing is the key here," said Mohammad Akhshik, principal investigator of the Hubble observing program. "It amplifies the light across all wavelengths so that it's easier to detect, and you also get higher spatial resolution when you have these galaxies stretched across the sky. You can essentially see inside of them at much finer physical scales to figure out what's happening."
Live Fast, Die Young
These sorts of dead galaxies don't appear to rejuvenate, even through later minor mergers and accretions of nearby, small galaxies and gas. Gobbling up things around them mostly just "puffs up" the galaxies. If star formation does turn back on, Whitaker described it as "a kind of a frosting." About 11 billion years later in the present-day universe, these formerly compact galaxies are thought to have evolved to be larger but are still dead in terms of any new star formation.
These six galaxies lived fast and furious lives, creating their stars in a remarkably short time. Why they shut down star formation so early is still a puzzle.
Whitaker proposes several possible explanations: "Did a supermassive black hole in the galaxy's center turn on and heat up all the gas? If so, the gas could still be there, but now it's hot. Or it could have been expelled and now it's being prevented from accreting back onto the galaxy. Or did the galaxy just use it all up, and the supply is cut off? These are some of the open questions that we'll continue to explore with new observations down the road."
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.
Media Contacts:
Claire Andreoli
NASA's Goddard Space Flight Center
301-286-1940
Ann Jenkins
Space Telescope Science Institute, Baltimore, Maryland
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
Science Contact:
Katherine E. Whitaker
University of Massachusetts, Amherst, Massachusetts
JOURNAL
Nature
METHOD OF RESEARCH
News article
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Quenching of star formation from a lack of inflowing gas to galaxies
ARTICLE PUBLICATION DATE
22-Sep-2021
Hubble finds distant galaxies that ran out of fuel
Peer-Reviewed PublicationIMAGE: THE GALAXY CLUSTER MACSJ0138.0-2155 MAGNIFIES AND DISTORTS THE IMAGE OF A GALAXY AT A DISTANCE OF 17 BILLION LIGHTYEARS, ENABLING ASTRONOMERS TO STUDY IT IN GREAT DETAIL. view more
CREDIT: ESA/HUBBLE & NASA, A. NEWMAN, M. AKHSHIK, K. WHITAKER
Using the Hubble Space Telescope, the ALMA radio telescope, and a "cosmic telescope" consisting of a massive cluster of galaxies, astronomers from the Cosmic Dawn Center — a collaboration between the Niels Bohr Institute at the University of Copenhagen and DTU Space at the Technical University of Denmark— have found six galaxies in the early Universe that have run out of gas to make new stars. How they ran out is a bit of a mystery.
Galaxies are full of stars, and stars are made from gas.
Nowadays, some galaxies have run out of gas for one reason or another, and hence stopped forming new stars, while others, by reusing gas from old stars or by accreting new gas from intergalactic space, are able to continue to form new stars.
Most stars were created in the early Universe when it was 1/5 of its current age, about 2–4 billion years after the Big Bang. Because light from distant galaxies takes time to reach us, we look further back in time the farther we look into space. If we look 10–12 billion years back in time, we therefore see predominantly strongly star-forming galaxies.
But now a team of astronomers, led by assistant professor Kate Whitaker from University of Massachusetts Amherst and associate faculty at the Danish Cosmic Dawn Center at the Niels Bohr Institute and DTU Space have, observed six massive galaxies in exactly this period which have mysteriously already used up their gas and stopped forming stars. The observations challenge our understanding of star formation and galaxy evolution.
Cosmic telescope
The observations that show these galaxies running on empty have been carried out with an array of radio antennas in Chile, called the Atacama Large Millimeter Array, or "ALMA". In order to find the galaxies in the first place, astronomers have taken advantage of the Hubble Space Telescope's high resolution.
Moreover, with the marvelous phenomenon known as "gravitational lensing", the astronomers were able to study this type of galaxies in unprecedented detail. The gravitational lenses in these six cases are intervening clusters of hundreds of galaxies, which with their enormous mass curve space itself so much that it focuses the light from the distant galaxies towards us.
This "cosmic telescope" magnifies the six galaxies and amplifies their light up to 30 times, allowing Kate Whitaker and her group to constrain the amount of gas to much lower limits than has previously been possible.
Requiem for a galaxy
What makes some galaxies stop forming stars and become inactive, or "quiescent", is an open question in astronomy. A criterion for star formation is that the galaxy must contain enough gas, and that this gas must not be too hot, because hot gas clouds are unable to clump and collapse into stars.
So while the discovery is long-yearned for, it is not a huge surprise to the astronomers.
"For a long time, we have suspected that running out of gas is one of the main reasons that some galaxies cease to form star. But now we have the evidence," explains Georgios Magdis, associate professor at the Cosmic Dawn Center and part of the team that discovered the six galaxies.
Detecting gas in distant dead galaxies is usually close to impossible because the galaxies are both too faint and too small to see sufficiently small details. But in an observational program — appropriately dubbed REsolving QUIEscent Magnified (REQUIEM) Galaxies — Kate Whitaker and her colleagues have nevertheless found some of these peculiar galaxies.
"By using strong gravitational lensing as a natural telescope, we can find the distant, most massive and first galaxies to shut down their star formation", Kate Whitaker explains.
Why the six REQUIEM galaxies shut down is still not clear.
Kate Whitaker proposes several possible explanations:
"Did a supermassive black hole in the galaxy's center turn on and heat up all the gas? If so, the gas could still be there, but now it's hot. Was the gas blown out of the galaxy? Or did the galaxy simply use it all up? These are some of the open questions that we'll continue to explore with new observations down the road."
The article has just been published in the journal Nature, and can be found here: https://www.nature.com/articles/s41586-021-03806-7
JOURNAL
Nature
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Exhausted gas reservoirs drive massive galaxy quenching in the early universe
ARTICLE PUBLICATION DATE
22-Sep-2021
ALMA scientists uncover the mystery of early massive galaxies running on empty
New study reveals that early galaxies have no fuel, and something is stopping them from refilling the tank
IMAGE: THIS COMPOSITE IMAGE OF GALAXY CLUSTER MACSJ 0138 SHOWS DATA FROM THE ATACAMA LARGE MILLIMETER/SUBMILLIMETER ARRAY (ALMA) AND NASA’S HUBBLE SPACE TELESCOPE. THE MAGNIFIED SECTION SHOWS A BRIGHT ORANGE/RED DOT, WHICH TRACES COLD DUST OBSERVED IN RADIO USING ALMA. THIS COLD DUST HELPS SCIENTISTS TO UNDERSTAND, BY INFERENCE, THE AMOUNT OF COLD HYDROGEN GAS—REQUIRED FOR THE FORMATION OF STARS—PRESENT IN THE GALAXIES IN THE CLUSTER. view more
CREDIT: ALMA (ESO/NAOJ/NRAO)/S. DAGNELLO (NRAO), STSCI, K. WHITAKER ET AL
Early massive galaxies—those that formed in the three billion years following the Big Bang—should have contained large amounts of cold hydrogen gas, the fuel required to make stars. But scientists observing the early Universe with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Hubble Space Telescope have spotted something strange: half a dozen early massive galaxies that ran out of fuel. The results of the research are published today in Nature.
Known as “quenched” galaxies—or galaxies that have shut down star formation—the six galaxies selected for observation from the REsolving QUIEscent Magnified galaxies at high redshift, or the REQUIEM survey, are inconsistent with what astronomers expect of the early Universe.
“The most massive galaxies in the Universe lived fast and furious, creating their stars in a remarkably short amount of time. Gas, the fuel of star formation, should be plentiful at these early times in the Universe,” said Kate Whitaker, lead author on the study, and assistant professor of astronomy at the University of Massachusetts, Amherst. “We originally believed that these quenched galaxies hit the brakes just a few billion years after the Big Bang. In our new research, we’ve concluded that early galaxies didn’t actually put the brakes on, but rather, they were running on empty.”
To better understand how the galaxies formed and died, the team observed them using Hubble, which revealed details about the stars residing in the galaxies. Concurrent observations with ALMA revealed the galaxies’ continuum emission—a tracer of dust—at millimeter wavelengths, allowing the team to infer the amount of gas in the galaxies. The use of the two telescopes is by careful design, as the purpose of REQUIEM is to use strong gravitational lensing as a natural telescope to observe dormant galaxies with higher spatial resolution. This, in turn, gives scientists a clear view of galaxies’ internal goings-on, a task often impossible with those running on empty.
“If a galaxy isn’t making many new stars it gets very faint very fast so it is difficult or impossible to observe them in detail with any individual telescope. REQUIEM solves this by studying galaxies that are gravitationally lensed, meaning their light gets stretched and magnified as it bends and warps around other galaxies much closer to the Milky Way,” said Justin Spilker, a co-author on the new study, and a NASA Hubble postdoctoral fellow at the University of Texas at Austin. “In this way, gravitational lensing, combined with the resolving power and sensitivity of Hubble and ALMA, acts as a natural telescope and makes these dying galaxies appear bigger and brighter than they are in reality, allowing us to see what’s going on and what isn’t.”
The new observations showed that the cessation of star formation in the six target galaxies was not caused by a sudden inefficiency in the conversion of cold gas to stars. Instead, it was the result of the depletion or removal of the gas reservoirs in the galaxies. "We don't yet understand why this happens, but possible explanations could be that either the primary gas supply fueling the galaxy is cut off, or perhaps a supermassive black hole is injecting energy that keeps the gas in the galaxy hot,” said Christina Williams, an astronomer at the University of Arizona and co-author on the research. “Essentially, this means that the galaxies are unable to refill the fuel tank, and thus, unable to restart the engine on star production.”
The study also represents a number of important firsts in the measurement of early massive galaxies, synthesizing information that will guide future studies of the early Universe for years to come. “These are the first measurements of the cold dust continuum of distant dormant galaxies, and in fact, the first measurements of this kind outside the local Universe,” said Whitaker, adding that the new study has allowed scientists to see how much gas individual dead galaxies have. “We were able to probe the fuel of star formation in these early massive galaxies deep enough to take the first measurements of the gas tank reading, giving us a critically missing viewpoint of the cold gas properties of these galaxies.”
Although the team now knows that these galaxies are running on empty and that something is keeping them from refilling the tank and from forming new stars, the study represents just the first in a series of inquiries into what made early massive galaxies go, or not. “We still have so much to learn about why the most massive galaxies formed so early in the Universe and why they shut down their star formation when so much cold gas was readily available to them,” said Whitaker. “The mere fact that these massive beasts of the cosmos formed 100 billion stars within about a billion years and then suddenly shut down their star formation is a mystery we would all love to solve, and REQUIEM has provided the first clue.”
About ALMA
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.
JOURNAL
Nature
ARTICLE TITLE
Exhausted gas reservoirs drive massive galaxy quenching in the early universe
ARTICLE PUBLICATION DATE
23-Sep-2021
CAPTION
This composite image of galaxy cluster MACSJ 0138 shows data from the Atacama Large Millimeter/submillimeter Array (ALMA) and NASA’s Hubble Space Telescope, as observed by REsolving QUIEscent Magnified galaxies at high redshift, or the REQUIEM survey. The early massive galaxies studied by REQUIEM were found to be lacking in cold hydrogen gas, the fuel required to form stars.
CREDIT
ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO), STScI, K. Whitaker et al
Running on empty: Research by UMass Amherst astronomers solves the 12-billion-year-old mystery of stalled galaxies
Unprecedent measurements confirm galaxies idle when
they run out of cold gas
Peer-Reviewed PublicationIMAGE: • THE SLUMBERING GIANT GALAXY AT THE CENTER OF THIS IMAGE IS 10 BILLION LIGHT-YEARS AWAY. view more
CREDIT: ESA/HUBBLE & NASA, A. NEWMAN, M. AKHSHIK, K. WHITAKER
AMHERST, Mass. – New research, published in Nature and led by the University of Massachusetts Amherst, has just answered one of the fundamental questions about our universe: Why did some of the oldest, most massive galaxies go quiescent early in their formation? The answer, we now know, is because they ran out of cold gas.
“The most massive galaxies in our universe formed incredibly early, just after the Big Bang happened, 14 billion years ago,” says Kate Whitaker, professor of astronomy at UMass Amherst. “But for some reason, they have shut down. They’re no longer forming new stars.” Star formation is one of the key ways that galaxies grow, and they’re said to have gone quiescent when they cease forming stars. Astronomers have known that these early, massive galaxies had gone quiescent, but until now, no one knew why.
To find the answer, Whitaker’s team, which includes Alexandra Pope, associate professor of astronomy, and Christina C. Williams, who received her Ph.D. in astronomy at UMass, devised an innovative pairing of telescopes. They used the Hubble Space Telescope, which sees ultraviolet to near-infrared light, including the light we can see with our own eyes, to detect these distant galaxies, which are so far away that we’re only just now seeing the light they emitted 10 billion to 12 billion years ago, when the universe was in its infancy. In effect, Whitaker’s team is looking into the deep past.
These galaxies should appear young and vigorous, with evidence of constant star formation. But they don’t, and Whitaker’s team combined Hubble’s images with extraordinarily sensitive readings from ALMA, the Atacama Large Millimeter/submillimeter Array, which detects radiation invisible to the naked eye.
ALMA let Whitaker’s team look for tiny amounts of cold gas — the main energy source fueling new star formation. “There was copious cold gas in the early universe, so these galaxies, from 12 billion years ago, should have plenty left in the fuel tank.” Instead, Whitaker and her team found only traces of cold gas located at each galaxy’s center. This means that, within the first few billion years of the universe’s existence, these galaxies either burned through their energy supplies, or ejected them and, furthermore, that something may be physically blocking each galaxy’s replenishment of cold gas.
Taken together, the research helps us to rewrite the early history of the universe so that we can get a clearer idea of how galaxies evolve. The team’s next step is to figure out how compact the remaining gas is in these quiescent galaxies and why it exists only in the galaxies’ center.
###
This research was supported by the Alfred P. Sloan Foundation, National Science Foundation, NASA Goddard Space Flight Center, European Research Council, Carlsberg Foundation, Villum Fonden, Canadian Space Agency, NASA and the Dunlap Institute for Astronomy & Astrophysics.
Contacts: Kate Whitaker, kwhitaker@astro.umass.edu
Daegan Miller, drmiller@umass.edu
JOURNAL
Nature
ARTICLE TITLE
Quenching of star formation from a lack of inflowing gas to galaxies
ARTICLE PUBLICATION DATE
22-Sep-2021
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