ALMA and the NSF VLA Use a Cosmic Lens to Reveal a Hyperactive Cradle of a Future Galaxy Cluster

PASASAGES Lensed Protocluster Core Candidate PJ0846+15

The galaxy cluster lens J0846 in optical light (bottom right), the ALMA view of dust-enshrouded, star-forming galaxies strongly lensed into bright arcs (top right), and a composite view (left) revealing at least 11 dusty galaxies in a compact protocluster core more than 11 billion light-years away, magnified by the foreground cluster’s gravity. Credit: NSF/AUI/NSF NRAO/B. Saxton; NSF/NOIRLab

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ALMA observations, together with NSF VLA, uncover the first strongly lensed protocluster core, revealing an intense burst of galaxy growth in the early universe

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA), together with the U.S. National Science Foundation Very Large Array (NSF VLA), have uncovered a rare, extraordinarily active region of the early universe where a future galaxy cluster is rapidly forming. By exploiting a powerful natural phenomenon known as gravitational lensing, ALMA revealed a compact, dust-enshrouded swarm of young galaxies forming stars at an exceptional rate more than 11 billion years ago.

The discovery marks the first strongly lensed protocluster core ever identified, providing an unprecedented, magnified view of one of the universe’s earliest large-scale structures in formation. Complementary observations with the NSF VLA helped characterize both the distant galaxies and the massive foreground cluster responsible for the lensing effect.

Galaxy clusters are the largest gravitationally bound structures in the universe. Their ancestors, known as protoclusters, are regions where galaxies are still assembling, rapidly converting gas into stars and growing in mass. Studying these systems allows astronomers to trace how today’s massive clusters emerged from much smaller, denser environments in the early cosmos.

ALMA’s high-resolution observations revealed that what initially appeared as a single bright source in all-sky survey data is actually a tightly packed group of at least 11 dusty, star-forming galaxies. These galaxies are confined to a region only a few hundred thousand light-years across — remarkably compact on cosmic scales — and are experiencing intense bursts of star formation.

Because these galaxies are heavily shrouded in dust, most of their visible light is absorbed and re-emitted at millimeter and submillimeter wavelengths. ALMA’s sensitivity to this cold dust and molecular gas allowed astronomers to detect the raw material fueling star formation and to measure the dynamics of the system with exceptional clarity.

The protocluster lies behind a massive foreground galaxy cluster whose gravity acts as a cosmic magnifying glass, bending and amplifying the light from the more distant system. This gravitational lensing effect dramatically boosts ALMA and the NSF VLA’s ability to resolve individual galaxies and study their properties in detail, effectively turning the universe itself into a telescope.

ALMA detected carbon monoxide (CO) emission, a key tracer of molecular gas, helping confirm that the galaxies share a common distance and form a physically connected structure. These observations show that the protocluster core contains enormous gas reservoirs capable of sustaining vigorous star formation and driving the rapid buildup of stellar mass.

Complementary observations with the NSF VLA provided radio-frequency data that helped map the foreground cluster and identify radio emission associated with both star formation and energetic processes within the system, strengthening the interpretation of the lensing configuration and the nature of the galaxies involved.

“Galaxy clusters are akin to a sprawling modern metropolis that was built upon an ancient civilization from the past. For example, if an archaeologist digs deeper into the ground, then they uncover an earlier civilization. Similarly, when astronomers observe objects farther away, they can look further back in time. In this way, the study of this distant protocluster gives us a glimpse into how one of the earliest ‘settlements’ of galaxies grew and evolved into the mature structures such as that foreground galaxy cluster that we observe today,” said Nicholas Foo, a graduate student at Arizona State University.

Protoclusters like this one represent the earliest construction phases of galaxy clusters seen in the present-day universe. By combining ALMA’s detailed view of cold gas and dust with complementary radio observations from the NSF VLA, astronomers can investigate how galaxies grow, interact, and evolve in the densest environments of the early cosmos.

This rare alignment of a young protocluster and a massive foreground lens provides an exceptional opportunity to test theories of galaxy and cluster formation. Future ALMA observations will further explore how these compact, dust-rich systems evolve and how their extreme environments shape the galaxies that will eventually populate massive clusters billions of years later.

Source: ALMA (Atacama Large Millimeter/submillimeter Array)/Press Release

Scientific Paper

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Additional Information

The results of this research appear as "PASSAGES: The Discovery of a Strongly Lensed Protocluster Core Candidate at Cosmic Noon" in the Astrophysical Journal by N. foo et al.

The original press release was published by the National Radio Astronomy Observatory of the United States, an ALMA partner, on behalf of North America.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (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 and Technology Council (NSTC) in Taiwan, 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 ALMA's construction, commissioning, and operation.

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Contacts:

Nicolás Lira
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Phone: +56 2 2467 6519
Email: nicolas.lira@alma.cl

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Bárbara Ferreira
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Yuichi Matsuda
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Astronomers Discover a Massive Galaxy 'Shipyard' in the Distant Universe

Several instruments joined forces to produce this image of the G237 protocluster, identifying its galaxies in different colors representing different wavelengths of observations. The image on the right zooms in on the central region of this massive galaxy “shipyard.” Credits: ESA/Herschel and XMM-Newton; NASA/Spitzer; NAOJ/Subaru; Large Binocular Telescope; ESO/VISTA. Polletta, M. et al. 2021; Koyama, Y. et al. 2021. Credits: ESA/Herschel and XMM-Newton; NASA/Spitzer; NAOJ/Subaru; Large Binocular Telescope; ESO/VISTA

Several instruments joined forces to produce this image of the G237 protocluster, identifying its galaxies in different colors representing different wavelengths of observations. The image on the right zooms in on the central region of this massive galaxy “shipyard.” Credits: ESA/Herschel and XMM-Newton; NASA/Spitzer; NAOJ/Subaru; Large Binocular Telescope; ESO/VISTA. Polletta, M. et al. 2021; Koyama, Y. et al. 2021. Credits: ESA/Herschel and XMM-Newton; NASA/Spitzer; NAOJ/Subaru; Large Binocular Telescope; ESO/VISTA

Even galaxies don't like to be alone. While astronomers have known for a while that galaxies tend to congregate in groups and in clusters, the process of going from formation to friend groups has remained an open question in cosmology.

In a paper published in the Astronomy & Astrophysics Journal, an international team of astronomers reports the discovery of objects that appear to be an emerging accumulation of galaxies in the making – known as a protocluster.

"This discovery is an important step toward reaching our ultimate goal: understanding the assembly of galaxy clusters, the most massive structures that exist in the universe," said Brenda Frye, an associate professor of astronomy at the University of Arizona's Steward Observatory and a co-author of the study.

To cite a local analog, the Milky Way, the galaxy that is home to our solar system, belongs to a galaxy cluster known as the Local Group, which in turn is a part of the Virgo supercluster. But what did a supercluster such as Virgo look like 11 billion years ago?

“We still know very little about protoclusters, in part because they are so faint, too faint to be detected by optical light,” Frye said. At the same time, they are known to radiate brightly in other wavelengths such as the sub-millimeter.”

Initially discovered by the European Space Agency’s Planck telescope as part of an all-sky survey, this protocluster showed up prominently in the far-infrared region of the electromagnetic spectrum. Sifting through a sample of more than 2000 candidate objects – structures that could be in the process of becoming clusters – the researchers came across a protocluster designated as PHz G237.01+42.50, or G237 for short. The observations looked promising, but to confirm its identity required follow-up observations with other telescopes.

Led by Mari Polletta at the National Institute for Astrophysics, or INAF in Milan, Italy, the team conducted the observations using the combined power of the Large Binocular Telescope in Arizona, which is managed by UArizona, and the Subaru Telescope in Japan. As a result of this combined study, the team identified 63 galaxies belonging to the G237 protocluster. The original discovery was published in a paper (https://ui.adsabs.harvard.edu/abs/2021MNRAS.503L...1K/abstract), and follow-up observations were also obtained using archival data, the Herschel Space Observatory, and the Spitzer Space Telescope.

"You can think of galaxy protoclusters such as G237 as a galaxy shipyard in which massive galaxies are being assembled, only this structure existed at a time when the universe was 3 billion years old," Frye said. "At the same time, the genealogy may be closer than you think. Because the universe is homogeneous and the same in all directions, we think that the Milky Way may have docked at a protocluster node similar to G237 when it was very young.”

At first, the observations of G237 implied a total star formation rate that was unrealistically high, and the team struggled to make sense of the data. The G237 protocluster seemed to be forming stars at a rate of 10,000 times that of the Milky Way, the authors note. At that rate, the protocluster is expected to rapidly use up its stellar fuel and subsequently settle down into a complex system similar to the Virgo supercluster.

"Each of the 63 galaxies discovered so far in G237 was like a star factory in overdrive," Frye said. "It's as if the galaxies were working on overtime to the assemble stars. The rate of production was unsustainable. As such a pace, the supply chains are expected to break in the near future, and in a way that permanently shuts down the galaxy shipyard.”

Such high yields can only be maintained by a continuous injection of fuel, which for stars is hydrogen gas. Frye said the result required an efficient and unbroken supply chain that drew in unreasonably-large amounts of fresh gas to fuel the star-forming factories.

"We don't know where that gas was coming from," she said.

Later, the team discovered that some of the light was coming from galaxies unrelated to the protocluster, but even after the irrelevant light was removed, the total star formation rate remained high, at least a thousand solar masses per year, according to Poletta. For comparison, the Milky Way produces about one solar mass each year.
“The picture we have pieced together now is that of a successful galaxy shipyard which is working at high efficiency to assemble galaxies and the stars within them and and has an energy supply that is more sustainable,” Frye said.

All galaxies in the universe are part of a giant structure that resembles a three-dimensional spider web shape called the cosmic web. The filaments of the cosmic web intersect at the nodes, which equate to the galaxy shipyards in the analogy used here.

“We believe that the filaments mediate the transfer of hydrogen gas from the diffuse medium of intergalactic space onto these hungry, newly forming protocluster structures in the nodes,” Frye said.

Pointing to future research, Polletta said: “We are in the process of analyzing more observations on this and other Planck protoclusters with the goal of tracing the gas that gives birth to these newly-forming stars and feeds the supermassive black holes, to determine its origin and explain the observed extraordinary activity.”

Frye said she is looking forward to combining data from the Large Binocular Telescope with planned observations using the James Webb Space Telescope, to be launched in December.

“Protoclusters offer an opportunity to investigate key questions in astronomy that only this new observatory can answer,” she said, “such as what mechanisms drive the prodigious star formation, and when will the hydrogen supply run out, forcing this galaxy shipyard to close its doors and turn into a supercluster similar to the one our Milky Way is in?”

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The two research papers are:

“A Planck-selected dusty protocluster at z=2.16 associated with a strong over-density of massive Hα emitting galaxies”, authored by Yusei Koyama, Maria del Carmen Polletta, Ichi Tanaka, Tadayuki Kodama, Hervé Dole, Geneviève Soucail, Brenda Frye, Matt Lehnert, Marco Scodeggio, 2021, MNRAS, 501, L1, Abstract here and publication here.

"Spectroscopic observations of PHz G237.01+42.50 : a galaxy protocluster at z=2.16 in the Cosmos field”, authored by M. Polletta, G. Soucail, H. Dole, M. D. Lehnert, E. Pointecouteau, G. Vietri, M. Scodeggio, L. Montier, Y. Koyama, G. Lagache, B. L. Frye, F. Cusano, and M. Fumana, 2021, A&A, Volume 654, A121.

The work reported here used different facilities around the world and in space:

• Subaru Telescope in Hawaii. MOIRCS: Multi-Object Infrared Camera and Spectrograph.
• Large Binocular Telescope in Arizona. Operated by different universities and research institutions in the USA, Germany, Italy. LUCI spectrograph — Large Binocular Telescope Near-infrared Spectroscopic Utility with Camera and Integral Field Unit for Extragalactic Research.
• Planck, an ESA mission dedicated to cosmology and the cosmic microwave background, observing the whole sky in the radio and sub-millimeter light
• ​Herschel, an ESA observatory dedicated to the cold and far-away universe, observing the far-infrared and sub-millimeter light
• ​Spitzer, a NASA great observatory observing in the infrared.

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Other links:

UA/LBTO pdf version of this PR here
UA News Release here
INAF Press Release (Italian) here​
CNRS Press Release (French) here
Subaru Press Release (Japanese - English)​

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About LBT

​The largest optical telescope in operation, the Large Binocular Telescope uses two 8.4-meter primary meters which offer the light gathering power of an 11.7m mirror and, when used in interferometric mode, the resolving power of an 22.7m telescope. A sophisticated Adaptive Optics System correcting for atmospheric disturbances enables LBT to generate crisp and clear images of the universe. Operated by the University of Arizona (UA) in Tucson, Arizona, USA, the LBT is an international collaboration of the UA, Italy (INAF: Istituto Nazionale di Astrofisica), Germany (LBTB: LBT Beteiligungsgesellschaft), and The Ohio State University (OSU) representing OSU, the University of Minnesota, the University of Virginia, and the University of Notre Dame. 

More information: http://www.lbto.org/

Source: Large Binocular Telescope Observatory (LBTO)

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“Yellowballs” Offer New Insights Into Star Formation

An example of a yellowball (left, circled) and a bubble (right, circled) as seen in infrared images from NASA's Spitzer Space Telescope. A typical yellowball has a diameter of about a light-year, while a bubble can grow to tens of light-years. This false-color image uses a blue-green-red color scheme to depict infrared wavelengths used in the Milky Way Project and gives rise to the ‘yellow’ color of the feature. Credit: NASA/JPL-Caltech.

A serendipitous discovery by citizen scientists has provided a unique new window into the diverse environments that produce stars and star clusters, revealing the presence of “stellar nurseries” before infant stars emerge from their birth clouds, according to Planetary Science Institute Senior Scientist Grace Wolf-Chase.

“Yellowballs are small compact features that were identified in infrared images acquired by the Spitzer Space Telescope during online discussions on the Milky Way Project, an initiative on the online citizen science platform zooniverse.org, that asked citizen scientists to help identify features associated with young, massive stars greater than 10 solar masses,” said Wolf-Chase, lead author of “The Milky Way Project: Probing Star Formation with First Results on Yellowballs from DR2” (https://doi.org/10.3847/1538-4357/abe87a) that appears in the Astrophysical Journal. “Early research suggested yellowballs are produced by young stars as they heat the surrounding gas and dust from which they were born.”

The yellowballs discovered by citizen scientists shed infrared light on a very early stage in the development of star clusters, when they are a ‘mere’ hundred thousand years old. “This is the point at which their presence is first revealed, but they remain embedded in their dusty birth cocoons,” Wolf-Chase said. “This allows us to link the properties of stars with their birth environments, as if a human were giving birth to a hundred or so infants at once.”

The research shows that forming star clusters – protoclusters – of essentially all masses go through a yellowball stage. Some of these protoclusters form massive stars greater than 10 solar masses that will sculpt their environments into “bubbles” through strong stellar winds and harsh ultraviolet radiation, while others won't. Over the course of a million years, bubbles can expand to tens of light years across.

“We also showed that we can glean information about the masses and ages of developing star clusters through the infrared ‘colors’ of yellowballs alone, without other extensive observations such as spectroscopy,” Wolf-Chase said. “This is important because observing time is limited and if we can tell a lot about thousands of these objects from a few, relatively simple observations, it's a great time-saver and helps us identify particularly interesting yellowballs for future higher-resolution observations.”

During the course of searching for ‘bubbles’ in the Milky Way Project, citizen scientists used the project’s discussion board to tag small, roundish, objects that appear “yellow” in the representative color infrared images. “Scientists initially thought these might be very young versions of the bubbles and we included identifying yellowballs as a principal goal in a version of the Milky Way Project that was launched in 2016,” Wolf-Chase said. “This resulted in the identification of 6,176 yellowballs over more than one-third of the Milky Way. Their distinctive ‘yellow’ appearance relates to wavelengths that trace complex organic molecules and dust as they are warmed by very young stars embedded in their birth clouds.”

“Our paper analyzes a subset of 516 yellowballs and shows only about 20% of yellowballs will form the bubbles associated with massive stars, while about 80% of these objects pinpoint the location of regions forming less massive stars,” Wolf-Chase said. “This work shows the great value of citizen science in opening a new window into our understanding of star formation.”

This image shows a swath of part of the Milky Way used in the analysis presented in the yellowballs paper. Yellowballs that represent regions which aren't associated with massive stars are circled. The image uses a green and red color scheme to highlight complex organic molecules and dust. Credit: Charles Kerton, Iowa State University/NASA/Spitzer

Media Contact:

Alan Fischer
Public Information Officer
520-382-0411
fischer@psi.edu

Science Contact:

Grace Wolf-Chase
Senior Scientist and Senior Education and Communication Specialist
630-414-2128
gwchase@psi.edu

Source: Planetary Science Institute (PSI)

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Dramatic Starbursts Hidden in Protoclusters at 12 Billion Years Ago

Figure 1: A schematic view of the image analysis in this work. First, the team selected protocluster candidates at 12 billion years ago from the deep and wide extragalactic survey with HSC. Then they used the archival full sky survey images at mid-far infrared taken by infrared space telescopes like Planck to investigate the infrared properties of galaxies in protoclusters. The spatial resolution and sensitivity of these images are too low to resolve distant galaxies individually, however, by stacking the images of the 180 protocluster candidates selected with HSC, the team successfully constrained the average total infrared flux of a protocluster. (Credit: NAOJ)

A team of astronomers from the National Astronomical Observatory of Japan (NAOJ) and the University of Tokyo has detected the strong infrared emissions from protoclusters at 12 billion years ago by using the deep and wide extragalactic survey with Hyper Suprime-Cam (HSC) on the Subaru Telescope and archival infrared data taken by various space telescopes. The detected infrared emissions were brighter than that which was expected from the galaxy population observed in the visible. These results indicate dramatic star formation and super massive black hole growth which are not observable in the optical but luminous in the infrared.

There are many galaxies in our Universe. There is an environmental dependence of galaxy type in that giant elliptical galaxies dominate galaxy overdense regions (clusters of galaxies) while spiral galaxies dominate general fields. To investigate how the environmental dependence of galaxies developed, the team studied progenitors of modern clusters of galaxies, called protoclusters. 

To constrain the typical properties of protoclusters, they needed to observe many protoclusters statistically. However, the surface number density of protoclusters is too low to search for them easily. Therefore, only a small number of protoclusters which existed over 10 billion years ago have been known. 

HSC on the Subaru Telescope enables an effective search for protoclusters. HSC is an optical camera with an extremely wide field of view (about 1.8 square degrees, equivalent to the area of nine full moons) and high sensitivity. Now, a deep and wide extragalactic survey is on-going with HSC (HSC-SSP). From the 120 square degree survey of the first HSC-SSP results, the team selected about 180 protocluster candidates. This is the largest catalog of protoclusters ever (March 4, 2018, Press Release from Subaru Telescope).

The Subaru Telescope is an optical telescope, but to study galaxy properties in more detail, observations at various wavelengths are needed. In the case of a rapidly star forming galaxy, most of the light from its young stars, which is an indicator of the star formation rate, is absorbed by its surrounding dust. The team needed to observe the infrared/radio emissions re-emitted from the dust to evaluate the star formation rate of a galaxy correctly. However, it is hard to observe in the infrared with ground-based telescopes because most of the infrared emissions are absorbed by water vapor in the atmosphere. There is no working space telescope with the sensitivity required to observe galaxies at 12 billion years ago in the infrared. ALMA can observe distant galaxies at radio wavelengths, however, its available wavelength range is limited and it is impractical to observe over 100 protoclusters.

To investigate the infrared properties of galaxies in protoclusters, the science team focused on the infrared data in public archives freely accessible to everyone. They used the archival full sky survey images at mid-far infrared taken by five (one is not a full sky survey) infrared space telescopes like Planck (Note 1). The spatial resolution and sensitivity of these images are too low to resolve distant galaxies individually, however, by stacking the images of the 180 protocluster candidates selected with HSC, they successfully constrained the average total infrared flux of a protocluster. Especially, the mid-far infrared flux (30-200 microns) of galaxies at 12 billion years ago has been unknown.

Figure 2: The derived average total infrared flux of a protocluster at 12 billion years ago. The red circles show the total fluxes from all the galaxies in a protocluster. Black points and the dotted line show the fluxes from a galaxy that was detected by HSC. The gray curve shows the infrared flux of a protocluster expected from the optical measurements by HSC. The dark gray region shows the difference in the flux between the actual infrared observations and the expectation from the HSC measurements. This difference implies that there are galaxies which are not observable in the optical but which are luminous in the infrared. (Credit: NAOJ)

Surprisingly, the average total infrared flux of a protocluster is brighter than that which was expected from the galaxy population found by HSC. This implies that there are galaxies which are not observable in the optical but which are luminous in the infrared.

What is the origin of this strong infrared emission? The team investigated the flux to wavelength distribution in the infrared and found that the average dust temperature of the protoclusters is warmer than that of a typical star forming galaxy. That implies that there are not only typical star forming galaxies but also growing super massive black holes at the centers of the galaxies (so called active galactic nuclei) and/or young hot dusty starburst galaxies which heat dust to higher temperatures. This study demonstrates the need to study protoclusters at wavelengths outside of the wavelength coverage of ground-based large telescopes like the Subaru Telescope and ALMA. 

To study the galaxies in protoclusters in more detail, individual protocluster galaxies need to be resolved in the mid to far-infrared, however, there is no telescope capable of such observations at this point. The leader of the team, Mariko Kubo (postdoctoral fellow at NAOJ) says, "In the future, SPICA, the future space telescope planned by Japan and ESA, will reveal the mid-far infrared forms of distant galaxies. On the other hand, unlike HSC, SPICA will not be made for wide field surveys. Our results partly complement SPICA's science."

This study was published in The Astrophysical Journal on December 20, 2019 (Mariko Kubo, Jun Toshikawa, Nobunari Kashikawa, Yi-Kuan Chiang, Roderik Overzier, Hisakazu Uchiyama, David L. Clements, David M. Alexander, Yuichi Matsuda, Tadayuki Kodama, Yoshiaki Ono, Tomotsugu Goto, Tai-An Cheng, and Kei Ito, 2019, ApJ 887, 214, "Planck Far-infrared Detection of Hyper Suprime-Cam Protoclusters at z∼4: Hidden AGN and Star Formation Activity"). This work was funded, in part, by the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (JP15H03645, JP17H04831, JP17KK0098, JP19H00697).

Source: Subaru Telescope

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Note 1: 

The science team used the data archived by the Planck, IRAS, WISE, Herschel, and AKARI space telescopes. These telescopes finished their missions a long time ago, but the data taken by them is in public data archives. Infrared space telescopes generally finish their lives within a few years because they have to load coolant (which should be exhausted) and operate in a harsh environment. For mid-infrared wavelength observations, the James Webb Space Telescope will be launched next year. However, there is no far-infrared observatory for distant galaxies between the Herschel space telescope, which finished its mission in 2013, and SPICA (planned to be launched in around 2030).

Links

• Double or Nothing: Astronomers Rethink Quasar Environment (March 4, 2018, Subaru Telescope Press Release)

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