Catching the edge of the Phantom Galaxy (NIRCam and MIRI image)

M74 and NGC 628 (Phantom Galaxy)

A large spiral galaxy takes up the entirety of the image. The core is mostly bright white, but there are also swirling, detailed structures that resemble water circling a drain. There is small white and pale blue light that emanates from stars and dust at the core’s centre, but it is tightly limited to the core. The rings feature colours of deep red and orange and highlight filaments of dust around cavernous black bubbles.

In August 2022, to mark the launch of the Picture of the Month series, ESA/Webb published a stunning image of the Phantom Galaxy (also known as M74 and NGC 628). Now, this series is revisiting the target to feature new data on this iconic spiral galaxy.

M74 resides around 32 million light-years away from Earth in the constellation Pisces, and lies almost face-on to Earth. This, coupled with its well-defined spiral arms, makes it a favourite target for astronomers studying the origin and structure of galactic spirals.

This image features data from two of Webb’s instruments: MIRI (Mid-InfraRed Instrument) and NIRCam (Near-InfraRed Camera). Observations in the infrared reveal the galaxy’s creeping tendrils of gas, dust and stars. In this image the dark red regions trace the filamentary warm dust permeating the galaxy. The red regions show the reprocessed light from complex molecules forming on dust grains, while orange and yellow colours reveal the regions of gas ionised by the recently formed star clusters. Stellar feedback has a dramatic effect on the medium within the galaxy and creates a complex network of bright knots as well as cavernous black bubbles. The lack of gas in the nuclear region of this galaxy also provides an unobscured view of the nuclear star cluster at the galaxy's centre. M74 is a particular class of spiral galaxy known as a ‘grand design spiral’, meaning that its spiral arms are prominent and well-defined, unlike the patchy and ragged structure seen in some spiral galaxies.

M74 was observed by Webb as part of a series of observations collectively entitled Feedback in Emerging extrAgalactic Star clusTers, or FEAST (PI: A. Adamo). Many other targets of the FEAST programme, including NGC 4449, M51, and M83, were the subjects of previous ESA/Webb Picture of the Month images in 2023 and 2024. The FEAST observations were designed to shed light on the interplay between stellar feedback and star formation in environments outside the Milky Way galaxy. Stellar feedback is the term used to describe the outpouring of energy from stars into the environments which form them, and is a process that contributes significantly to determining the rates at which stars form. Understanding stellar feedback is vital for building accurate universal models of star formation.

The new Webb data obtained by the FEAST team has allowed scientists to look at the stellar nurseries in galaxies that are many light years away. Astronomers are learning how other galaxies are forming stars and how stars actively participate to model the galaxy interstellar medium. They have found that newly born stars slowly carve they gas and dust nurseries modifying the morphological appearance and essentially destructing them, as Webb has shown that this evolution is connected with star clusters. Furthermore, the team has concluded from their studies that the spiral arms captured by the extended coverage of the FEAST programme are the places where stars are forming more actively in the galaxy. The brighter and larger complexes of stellar nurseries are in the spiral arms fully captured by the new Webb data. The telescope is now revealing the map of hydrogen emission lines in the near-infrared. These lines are less affected than the dusts and reveals the places where new massive stars have just formed.

Links

• M74 (NIRCam image)
• Pan video: NIRCam and MIRI
• Pan video: NIRCam
• Video transitoning between images
• Science paper (A. Pedrini et al.)
• Science paper (B. Gregg et al.)

Source: ESA/Webb/potm

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Listen to the Universe: New NASA Sonifications and Documentary

IC 443 (Jellyfish Nebula)/M74 (Phantom Galaxy)/MSH 15-52 / PSR B1509-58

Credit Chandra X-ray: NASA/CXC/B.Gaensler et al; ROSAT X-ray: NASA/ROSAT/Asaoka & Aschenbach; Radio Wide: NRC/DRAO/D.Leahy; Optical: DSS; Sonification: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

JPEG (402 kb) - Large JPEG (7.2 MB) - Tiff (53.7 MB) - More Image

Tour: Listen to the Universe - More Videos

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Three new sonifications of images from NASA’s Chandra X-ray Observatory and other telescopes have been released. This work is also being featured in a new NASA+ documentary, "Listen to the Universe."

Sonification is the process of translating data into sounds. In the case of Chandra and other telescopes, scientific data are collected from space as digital signals that are commonly turned into visual imagery. The sonification project takes these data through another step of mapping the information into sound.

IC 443 (Jellyfish Nebula) (above)

IC 443 is a supernova remnant, or the debris of an exploded star, which astronomers have nicknamed the Jellyfish Nebula. A visual composite image of IC 443 includes X-rays from NASA’s Chandra X-ray Observatory and German ROSAT X-ray telescope (blue) along with radio data from the NSF’s Very Large Array (green) and optical data from the Digitized Sky Survey (red). The sonification of IC 443 begins with a top-down scan as the brightness of the data is correlated to the volume of the sound. The sounds are mapped to colors in the image with red light being heard as lower pitches, the green as medium, and the blue light as the higher pitches. This creates notes that sweep up and down in pitch continuously. Several colors are isolated and control the volume of sustained tones with red controlling the lowest note and white controlling the highest note. The background stars in the optical image have been converted to water drop sounds in the sonification.

M74 (Phantom Galaxy):

SonificationMessier 74 is a spiral galaxy like our Milky Way, which is seen face-on from Earth’s vantage point some 32 million light-years away. X-rays from Chandra (purple) have been combined with an infrared view of M74 from NASA’s James Webb Space Telescope (green, yellow, red, and magenta) as well as optical data from NASA’s Hubble Space Telescope (orange, cyan, and blue). In sonifying these data, a clockwise-moving radar-like scan starts around 12 o’clock. The distance from the center controls the frequencies of sound with light farther from the center being higher pitched. The Chandra sources correspond to relatively high musical pitches of glassy ethereal and clear plucked sounds. In the Webb data, large, medium, and small features are represented by low, medium, and high frequency ranges of pitches respectively with the brightest stars being heard as percussive sounds. The Hubble data have been turned into breathy synthesizer sounds along with thin metallic plucked sounds for bright stars and clusters.

MSH 15-52 / PSR B1509-58:

The third new sonification is of MSH 15-52, a cloud of energized particles blown away from a dead, collapsed star. This image includes X-rays from the Imaging X-ray Polarimetry Explorer, or IXPE, (purple) as well as Chandra (orange, green, and blue). These data have been combined with infrared data from the Dark Energy Plane Survey 2 (red and blue). In sound, the scan goes from the bottom to the top. The brightness of the Chandra data of the cloud have been converted into rough string-like sounds, while the blast wave is represented by a range of pitches of firework-type noises. The IXPE data are heard as wind-like sounds. The infrared data are mapped to musical pitches of a synthesizer sound. The light curve, or brightness over time, from the dead star’s collapsed core is heard in pulses that occur almost 7 times every second as it does in the original data.

These sonifications were led by the Chandra X-ray Center (CXC) and included as part of NASA's Universe of Learning (UoL) program. The collaboration was driven by visualization scientist Kimberly Arcand (CXC), astrophysicist Matt Russo, and musician Andrew Santaguida, (both of the SYSTEM Sounds project), along with consultant Christine Malec.

NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts. NASA's Universe of Learning materials are based upon work supported by NASA under cooperative agreement award number NNX16AC65A to the Space Telescope Science Institute, working in partnership with Caltech/IPAC, Center for Astrophysics | Harvard & Smithsonian, and the Jet Propulsion Laboratory.

Listen to the Universe (Documentary Trailer)

Source: NASA's Chandra X-Ray Observatory

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Visual Description:

The first image in this release is the Jellyfish Nebula, also called IC 443. This supernova remnant is shaped like a huge, colorful bubble containing shades of pink, blue, red, and green. Cloud-like structures, both inside the bubble and stretching outside of the bubble to our right and upper left, are filamentary in nature, as if fingers pulled at the edges of a cotton ball. Stars, seen as red dots, are flecked across the entire image.

The second image is Messier 74, a spiral galaxy like our own Milky Way. Seen face-on from our vantage point on Earth, the galaxy's sparkling arms spiral out from a bright white core. The core appears vibrant and alive, and crackles with lightning-like, pale blue light. Glowing, high-energy stars in purple, white, and orange, dot the lengths of the spiraling arms. Webs of murky dust crisscross the space between the curving silver blue arms, also known as dust lanes.

The last image is MSH 15-52, a pulsar wind nebula, which strongly resembles a ghostly purple hand with sparkling fingertips. A pulsar is a highly magnetized collapsed star that rotates and creates jets of matter flowing away from its poles. These jets, along with intense winds of particles, form pulsar wind nebulae. Here, the pulsar wind nebula known as MSH 15-52 resembles a hazy purple cloud set against a black, starry backdrop.

The shape of this pulsar wind nebula strongly resembles a human hand, including five fingers, a palm and wrist. The bright white spot near the base of the palm is the pulsar itself. The three longest fingertips of the hand shape point toward our upper right, or 1:00 on a clock face. There, a small, mottled, orange and yellow cloud appears to sparkle or glow like embers. This orange cloud is part of the remains of the supernova explosion that created the pulsar. The backdrop of stars was captured in infrared light.

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Fast Facts for IC 443 (Jellyfish Nebula):

Credit: Chandra X-ray: NASA/CXC/B.Gaensler et al; ROSAT X-ray: NASA/ROSAT/Asaoka & Aschenbach; Radio Wide: NRC/DRAO/D.Leahy; Optical: DSS; Sonification: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

About the Sound

Top-down scan with brightness controlling volume
Colors appearing in the nebula are mapped to sound in two ways.

Redder light is mapped to lower pitches while bluer light is mapped to higher pitches. This creates notes that sweep up and down in pitch continuously.
Several colors are isolated and control the volume of sustained tones with red controlling the lowest note and white controlling the highest note.
Background stars are converted to water drop sounds. The brightness of each star is mapped to volume and pitch and reverb is controlled by the brightness of the nebula in front of them.

Scale: The image is about 46.5 arcmin across (66 light-years across)
Category: Neutron Stars/X-ray Binaries, Supernovas & Supernova Remnants
Coordinates (J2000): RA 06h 17m 05.20s | Dec +22° 21´ 26.70"
Constellation: Gemini
Observation Date: January 12, 2005
Observation Time: 11 hours
Obs. ID: 5531
Instrument: ACIS
References: B. Gaensler et al. 2006, arXiv: astro-ph/0601304v2
Color Code: X-ray: blue; Radio: green; Optical: red
Distance Estimate: About 5,000 light-years

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Fast Facts for M74 (Phantom Galaxy):

Credit: X-ray: NASA/CXC/SAO; Optical: ESA/Hubble & NASA; IR: ESA/Webb, NASA & CSA, J. Lee and the PHANGS-JWST Team; Image Processing: N. Wolk and K. Arcand; Sonification: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

About the Sound:

Radar-like scan, clockwise from 12:00.

Brightness is mapped to volume and the distance from the center is mapped to pitch is various ways (farther from the center is higher pitched).

Binaural panning moves the apparent position of the sound clockwise around the listener’s head.

Infrared (JWST)

Distance from the center controls the pitch with large, medium, and small scale features mapped to low, med, and high ranges of frequencies.
Bright stars appearing red are accompanied by a percussive sound.

Optical (HST)

The distance from the center is mapped to musical pitches of a breathy synth sound.
Bright stars and clusters are rendered as thin plucked sounds.

X-ray (Chandra)

The distance from the center is mapped to high musical pitches of a glassy ethereal sound.
Compact sources are rendered as high musical pitches of a clear plucked sound.

Scale: Image is about 3.4 arcmin (32,000 light-years) across
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 1h 36m 42s | Dec +15° 47´ 01"
Constellation: Pisces
Observation Date: 13 observations from Jun 2001-Nov 2019
Observation Time: 81 hours 48 minutes (3 days 9 hours 48 minutes)
Obs. ID: 2057, 2058, 4753, 4854, 14801, 16000-16003, 16484, 16485, 20333, 21000
Instrument: ACIS
Color Code: X-ray: purple; Optical: orange, cyan, blue, IR: green, yellow, red, magenta
Distance Estimate: About 32 million light-years

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Fast Facts for MSH 15-52 / PSR B1509-58:

Credit: X-ray: NASA/CXC/Stanford Univ./R. Romani et al. (Chandra); NASA/MSFC (IXPE); Infrared: NASA/JPL-Caltech/DECaPS; Image Processing: NASA/CXC/SAO/J. Schmidt; Sonification: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

About the Sound

Bottom to top scan with brightness converted to audio frequency and volume using various techniques.
Horizontal position in the image is reflected in the stereo position of the sound.
Chandra (X-ray)

Brightness of pulsar nebula mapped to musical pitch on a rough string-like sound.
Brightness of blastwave emission mapped to pitch of affected fireworks sounds.

IXPE (X-ray)

Brightness mapped to continuous audio frequencies producing a wind-like sound.

DECAPS

The brightness of stars is mapped to musical pitches with a dreamy percussive synthesizer sound.

Pulsar Lightcurve

The composite includes a real-time sonification of the central pulsar’s X-ray emission (NuSTAR) which exhibits pulses 6.67 times every second. Its volume is loudest as the scanning line passes the pulsar itself.

Scale: Image is about 20 arcmin (93 light-years) across
Category: Supernovas & Supernova Remnants, Neutron Stars/X-ray Binaries
Coordinates (J2000): RA 15h 13m 55.52s | Dec -59° 08´ 08.8"
Constellation: Circinus
Observation Date: 10 pointings between 14 Aug 2000 and 19 June 2008
Observation Time: 93 hours 50 minutes (3 days 21 hours 50 minutes)
Obs. ID: 754, 3833, 3834, 4384, 5534, 5535, 5562, 6116, 6117, 9138
Instrument: ACIS
References: Romani, R. et al., ApJ, 2023; arXiv:2309.16067
Color Code: X-ray: orange, green, blue (Chandra), purple (IXPE); Infrared: red, blue
Distance Estimate: About 16,000 light-years

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NASA’s Webb Reveals Intricate Networks of Gas and Dust in Nearby Galaxies

NGC 1433 (MIRI Image)
Credits: Science: NASA, ESA, CSA, Janice Lee (NOIRLab)
Image Processing: Alyssa Pagan (STScI)

NGC 7496 (MIRI Image)
Science: NASA, ESA, CSA, Janice Lee (NOIRLab)
Image Processing: Joseph DePasquale (STScI)

NGC 1365 (MIRI Image)
Credits: Science: NASA, ESA, CSA, Janice Lee (NOIRLab)
Image Processing: Alyssa Pagan (STScI)

Release Images

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Researchers using NASA’s James Webb Space Telescope are getting their first look at star formation, gas, and dust in nearby galaxies with unprecedented resolution at infrared wavelengths. The data has enabled an initial collection of 21 research papers which provide new insight into how some of the smallest-scale processes in our universe – the beginnings of star formation – impact the evolution of the largest objects in our cosmos: galaxies.

The largest survey of nearby galaxies in Webb’s first year of science operations is being carried out by the Physics at High Angular resolution in Nearby Galaxies (PHANGS) collaboration, involving more than 100 researchers from around the globe. The Webb observations are led by Janice Lee, Gemini Observatory chief scientist at the National Science Foundation’s NOIRLab and affiliate astronomer at the University of Arizona in Tucson.

The team is studying a diverse sample of 19 spiral galaxies, and in Webb’s first few months of science operations, observations of five of those targets – M74, NGC 7496, IC 5332, NGC 1365, and NGC 1433 – have taken place. The results are already astounding astronomers.

“The clarity with which we are seeing the fine structure certainly caught us by surprise,” said team member David Thilker of Johns Hopkins University in Baltimore, Maryland.

“We are directly seeing how the energy from the formation of young stars affects the gas around them, and it’s just remarkable,” said team member Erik Rosolowsky of the University of Alberta, Canada.

The images from Webb’s Mid-Infrared Instrument (MIRI) reveal the presence of a network of highly structured features within these galaxies – glowing cavities of dust and huge cavernous bubbles of gas that line the spiral arms. In some regions of the nearby galaxies observed, this web of features appears built from both individual and overlapping shells and bubbles where young stars are releasing energy.

“Areas which are completely dark in Hubble imaging light up in exquisite detail in these new infrared images, allowing us to study how the dust in the interstellar medium has absorbed the light from forming stars and emitted it back out in the infrared, illuminating an intricate network of gas and dust,” said team member Karin Sandstrom of the University of California, San Diego.

The high-resolution imaging needed to study these structures has long evaded astronomers – until Webb came into the picture. “The PHANGS team has spent years observing these galaxies at optical, radio, and ultraviolent wavelengths using NASA’s Hubble Space Telescope, the Atacama Large Millimeter/Submillimeter Array, and the Very Large Telescope’s Multi Unit Spectroscopic Explorer,” added team member Adam Leroy of the Ohio State University. “But, the earliest stages of a star’s lifecycle have remained out of view because the process is enshrouded within gas and dust clouds.”

Webb’s powerful infrared capabilities can pierce through the dust to connect the missing puzzle pieces.

For example, specific wavelengths observable by MIRI (7.7 and 11.3 microns) and Webb’s Near-Infrared Camera (3.3 microns) are sensitive to emission from polycyclic aromatic hydrocarbons, which play a critical role in the formation of stars and planets. These molecules were detected by Webb in the first observations by the PHANGS program.

Studying these interactions at the finest scale can help provide insights into the larger picture of how galaxies have evolved over time.

“Because these observations are taken as part of what's called a treasury program, they are available to the public as they are observed and received on Earth,” said Eva Schinnerer of the Max Planck Institute for Astronomy in Heidelberg, Germany, and leader of the PHANGS collaboration.

The PHANGS team will work to create and release data sets that align Webb’s data to each of the complementary data sets obtained previously from the other observatories, to help accelerate discovery by the broader astronomical community.

“Thanks to the telescope's resolution, for the first time we can conduct a complete census of star formation, and take inventories of the interstellar medium bubble structures in nearby galaxies beyond the Local Group,” Lee said. “That census will help us understand how star formation and its feedback imprint themselves on the interstellar medium, then give rise to the next generation of stars, or how it actually impedes the next generation of stars from being formed.”

The research by the PHANGS team is being conducted as part of General Observer program 2107. The team’s initial findings, comprised of 21 individual studies, were recently published in a special focus issue of The Astrophysical Journal Letters.

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency), and CSA (Canadian Space Agency).

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About This Release

Credits:

Media Contact:

Hannah Braun
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science:

Janice Lee (NOIRLab), Eva Schinnerer

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents:

• ApJL PHANGS Special Issue

Source: NASA's James Webb Space Telescope/News

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What 100,000 Star Factories in 74 Galaxies Tell Us about Star Formation across the Universe

 

Six ALMA-imaged galaxies out of a collection of the 74. The images were taken as part of the PHANGS-ALMA survey to study the properties of star-forming clouds in disk galaxies. Credit: ALMA (ESO/NAOJ/NRAO); NRAO/AUI/NSF, B. Saxton. Hi-res image

ALMA image of galaxy NGC 4321, also known as Messier 100, an intermediate spiral galaxy located about 55 million light-years from Earth in the constellation Coma Berenices. It is imaged as part of the PHANGS-ALMA survey to study the properties of star-forming clouds in disk galaxies. Credit: ALMA (ESO/NAOJ/NRAO); NRAO/AUI/NSF, B. Saxton. Hi-res image

ALMA image of NGC 628, also known as Messier 74, a spiral galaxy in the constellation Pisces, located approximately 32 million light-years from Earth. It is imaged as part of the PHANGS-ALMA survey to study the properties of star-forming clouds in disk galaxies. Credit: ALMA (ESO/NAOJ/NRAO); NRAO/AUI/NSF, B. Saxton. Hi-res image

Composite ALMA (orange) and Hubble (blue) image of NGC 628, also known as Messier 74, a spiral galaxy in the constellation Pisces, located approximately 32 million light-years from Earth. It is imaged as part of the PHANGS-ALMA survey to study the properties of star-forming clouds in disk galaxies. Credit: NRAO/AUI/NSF, B. Saxton: ALMA (ESO/NAOJ/NRAO); NASA/Hubble. Hi-res image


Galaxies come in a wide variety of shapes and sizes. Some of the most significant differences among galaxies, however, relate to where and how they form new stars. Compelling research to explain these differences has been elusive, but that is about to change. The Atacama Large Millimeter/submillimeter Array (ALMA) is conducting an unprecedented survey of nearby disk galaxies to study their stellar nurseries. With it, astronomers are beginning to unravel the complex and as-yet poorly understood relationship between star-forming clouds and their host galaxies.

A vast, new research project with ALMA, known as PHANGS-ALMA (Physics at High Angular Resolution in Nearby GalaxieS), delves into this question with far greater power and precision than ever before by measuring the demographics and characteristics of a staggering 100,000 individual stellar nurseries spread throughout 74 galaxies.

PHANGS-ALMA, an unprecedented and ongoing research campaign, has already amassed a total of 750 hours of observations and given astronomers a much clearer understanding of how the cycle of star formation changes, depending on the size, age, and internal dynamics of each individual galaxy. This campaign is ten- to one-hundred-times more powerful (depending on your parameters) than any prior survey of its kind.

“Some galaxies are furiously bursting with new stars while others have long ago used up most of their fuel for star formation. The origin of this diversity may very likely lie in the properties of the stellar nurseries themselves,” said Erik Rosolowsky, an astronomer at the University of Alberta in Canada and a co-Principal Investigator of the PHANGS-ALMA research team.

He presented initial findings of this research at the 233rd meeting of the American Astronomical Society being held this week in Seattle, Washington. Several papers based on this campaign have also been published in the Astrophysical Journal and the Astrophysical Journal Letters. 

“Previous observations with earlier generations of radio telescopes provide some crucial insights about the nature of cold, dense stellar nurseries,” Rosolowsky said. “These observations, however, lacked the sensitivity, fine-scale resolution, and power to study the entire breadth of stellar nurseries across the full population of local galaxies. This severely limited our ability to connect the behavior or properties of individual stellar nurseries to the properties of the galaxies that they live in.”

For decades, astronomers have speculated that there are fundamental differences in the way disk galaxies of various sizes convert hydrogen into new stars. Some astronomers theorize that larger, and generally older galaxies, are not as efficient at stellar production as their smaller cousins. The most logical explanation would be that these big galaxies have less efficient stellar nurseries. But testing this idea with observations has been difficult.

For the first time, ALMA is allowing astronomers to conduct the necessary wide-ranging census to determine how the large-scale properties (size, motion, etc.) of a galaxy influence the cycle of star formation on the scale of individual molecular clouds. These clouds are only about a few tens to a few hundreds of light-years across, which is phenomenally small on the scale of an entire galaxy, especially when seen from millions of light-years away.

“Stars form more efficiently in some galaxies than others, but the dearth of high-resolution, cloud-scale observations meant our theories were weakly tested, which is why these ALMA observations are so critical,” said Adam Leroy, an astronomer at The Ohio State University and co-Principal Investigator on the PHANGS-ALMA team.

Part of the mystery of star formation, the astronomers note, has to do with the interstellar medium – all the matter and energy that fills the space between the stars.

Astronomers understand that there is an ongoing feedback loop in and around the stellar nurseries. Within these clouds, pockets of dense gas collapse and form stars, which disrupts the interstellar medium.

“Indeed, comparing early PHANGS observations with the locations of newly formed stars shows that the newly formed stars quickly destroy their birth clouds,” said Rosolowsky. “The PHANGS team is studying how this disruption plays out in different types of galaxies, which may be a key factor in star-forming efficiency.”

For this research, ALMA is observing molecules of carbon monoxide (CO) from all relatively massive, generally face-on spiral galaxies visible from the Southern Hemisphere. Molecules of CO naturally emit the millimeter-wavelength light that ALMA can detect. They are particularly effective at highlighting the location of star-forming clouds.

“ALMA is a stunningly efficient machine to map carbon monoxide over large areas in nearby galaxies,” said Leroy. “It was able to perform this survey because of the combined power of the 12-meter dishes, which study fine-scale features, and the smaller, 7-meter dishes at the center of the array, which are sensitive to large-scale features, essentially filling in the gaps.”

A companion survey, PHANGS-MUSE, is using the Very Large Telescope to obtain optical imaging of the first 19 galaxies observed by ALMA. MUSE stands for the Multi-Unit Spectroscopic Explorer. Another survey, PHANGS-HST uses the Hubble Space Telescope to survey 38 of these galaxies to find their youngest stellar clusters. Together, these three surveys give a startlingly complete picture of how well galaxies form stars by probing cold molecular gas, its motion, the location of ionized gas (regions where stars are already forming), and the galaxies’ complete stellar populations.

“In astronomy, we have no ability to watch the cosmos change over time; the timescales simply dwarf human existence,” noted Rosolowsky. “We can’t watch one object forever, but we can observe hundreds of thousands of star-forming clouds in galaxies of different sizes and ages to infer how galactic evolution works. That is the real value of the PHANGS-ALMA campaign.”

“We also look at thousands to tens of thousands of star-forming regions within each galaxy, catching them across their life cycle. This lets us build a picture of the birth and death of stellar nurseries across galaxies, something almost impossible before ALMA,” added Leroy.

So far, PHANGS-ALMA has studied about 100,000 Orion Nebula-like objects in the nearby universe. It is expected that the campaign will eventually observe around 300,000 star-forming regions.

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Additional Information

These results are being published in a series of papers in the Astrophysical Journal and the Astrophysical Journal Letters. Already accepted and published:

“Cloud-scale Molecular Gas Properties in 15 Nearby Galaxies,” J. Sun, et al., 2018 June. 25, Astrophysical Journal [http://iopscience.iop.org/article/10.3847/1538-4357/aac326]

“Star Formation Efficiency per Free-fall Time in nearby Galaxies,” D. Utomo, et al., 2018 July 11, Astrophysical Journal Letters [http://iopscience.iop.org/article/10.3847/2041-8213/aacf8f/meta]

“A 50 pc Scale View of Star Formation Efficiency across NGC 628,” K. Kreckel, et al., 2018 August 14, Astrophysical Journal Letters [http://iopscience.iop.org/article/10.3847/2041-8213/aad77d]

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 Ministry of Science and Technology (MOST) 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 the construction, commissioning and operation of ALMA.

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Contacts

Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
Email: nicolas.lira@alma.cl

Charles E. Blue
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia - USA
Phone: +1 434 296 0314
Cell phone: +1 202 236 6324
Email: cblue@nrao.edu

Calum Turner
ESO Assistant Public Information Officer
Garching bei München, Germany
Phone: +49 89 3200 6670
Email: calum.turner@eso.org

Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory
, Tokyo - Japan
Phone: +81 422 34 3630
Email: hiramatsu.masaaki@nao.ac.jp

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

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The Distribution of Atomic Hydrogen in Simulated Galaxies

In simulated galaxies of the hydrodynamical cosmological “EAGLE” simulation the distribution of atomic hydrogen agrees with observations in unprecedented detail. This success means that EAGLE can aid astrophysicists to better understand the processes shaping real galaxies, such as the origin of their atomic hydrogen. EAGLE is not quite perfect, however: the study also found that some simulated galaxies contain unphysically large holes in their atomic hydrogen discs, meaning further work for simulators to improve the models underlying the treatment of supernova explosions and the interstellar matter.

Fig. 1:  Observed distribution of atomic hydrogen (blue) in the nearby galaxy M74. Also shown are old stars (red) and UV radiation emitted by newborn stars (purple) - both of these are more strongly concentrated towards the galaxy’s centre than the atomic hydrogen. The green bar shows a length of 15 000 light years. Image: THINGS survey

Atomic hydrogen (abbreviated as “H I”) is an important component of galaxies, it is believed to feed the dense ‘interstellar matter’ from which stars can form. Although invisible to optical telescopes, astronomers have been able to make ever more accurate observations of this gas component using radio telescopes: this has revealed, for instance, that galaxies with the same stellar mass can differ in their H I content by more than an order of magnitude. By combining several radio antennas into one `supertelescope’ with the aid of interferometry it has also become possible to create high resolution maps showing the distribution of atomic hydrogen within individual galaxies (for an example, see Fig. 1).

But despite this wealth of observational data, astronomers are still puzzled by the question of why some galaxies contain so much more H I than others, and especially why `normal’ and `H I-rich’ galaxies still appear to follow common relations, as shown recently by the MPA-led “Bluedisk” project (see monthly highlights May 2013 and March 2014). A fundamental problem is that galaxies only evolve over periods of many millions of years, so that it is impossible to directly observe how the H I reservoir is built up. Instead, astronomers have to try and answer this question with the aid of models and simulations.

Fig. 2:  Gas in the large EAGLE simulation. Blue represents “cold” gas (T greater then 30,000 K), green warm, and red the hottest gas with T > 300,000 K. The small insets zoom in towards a single galaxy, highlighting the huge dynamic range of the simulation. © Richard Bower / James Trayford, ICC Durham

An international collaboration has recently completed the “EAGLE” simulation of galaxies which matches observed galaxies in several properties such as their stellar mass and size with unprecedented accuracy (see Fig. 2). A research team led by MPA scientist Yannick Bahe has now studied how well these simulated galaxies agree with real ones in terms of their atomic hydrogen content: an important test for the simulation model, which also determines whether EAGLE can give trustworthy clues on the evolution of H I in real galaxies.

To make this comparison, the scientists first had to post-process the simulation and calculate how much of the hydrogen in each simulation particle is actually atomic, i.e. not ionised or molecular. Once this was done, the total mass of H I in over 2000 simulated galaxies could be computed and compared to observational data from the “GASS” project. The resulting match between simulation and data is extremely good: it represents a significant improvement compared to previous simulations and indicates that the models used in EAGLE provide a reasonable description of the physical processes involved in forming galaxies.

Fig. 3:  The surface density of atomic hydrogen, plotted against distance from the galaxy centre. Yellow and blue bands show data from the “Bluedisk” project, comparing galaxies with normal (yellow) and exceptionally high (blue) total atomic hydrogen content. Red and green circles show simulated galaxies from EAGLE in the same categories. © MPA

 
Motivated by this initial success, the scientists tested the EAGLE simulations in more detail by comparing not just the total mass of H I, but also its distribution within galaxies to observations. The above-mentioned “Bluedisk” project has shown that this distribution is surprisingly independent of the total mass of H I as long as the galaxies’ H I discs are scaled to a common size (so called “self-similarity”). For an accurate comparison, the team now ‘observed’ the EAGLE galaxies in the same way as was done in Bluedisk. As can be seen in Fig. 3, both agree surprisingly well: EAGLE reproduces both the self-similarity between ‘normal’ and ‘H I-rich’ galaxies (red and green symbols in Fig. 3) and the detailed shape of the surface density profile – at least in the outer parts of the simulated galaxies.

In the central regions, however, EAGLE galaxies typically contain not enough atomic hydrogen. To test this discrepancy further, the scientists inspected more than 2000 images of the simulated galaxies, which finally gave the crucial clue: many simulated galaxies contain ‘holes’ in their hydrogen discs that are much larger than what is seen in observations. Once all simulated galaxies showing these large holes were excluded, the density profiles matched observations almost perfectly even in the centre.

Fig. 4:  Synthetic image showing atomic hydrogen in a simulated galaxy, in analogy to Fig. 1. 
Clearly visible are a number of large holes in the hydrogen disc. © MPA

Why, now, do some EAGLE galaxies contain these large holes? The scientists have not yet found a definitive answer, but it is likely that the way in which supernova explosions are modelled in the simulation plays a major role. This critical part of galaxy formation is still causing headaches for simulators: to include them in galaxy simulations in a fully self-consistent fashion, the resolution of the simulations would need to go up by many orders of magnitude. This will be, regrettably, impossible for a long time to come – even the biggest supercomputers today are just not big enough (see also highlight August 2015). As a result, EAGLE has to resort to using a highly simplified model for the effects of such supernovae. Another simplified model has to be employed for the dense interstellar matter, because a resolution level that would allow a fully self-consistent treatment can also not yet be achieved in simulations of a representative portion of the Universe. Although these simplified models produce galaxies which are realistic in many ways – such as their size – they do leave a noticeable artefact in some of the simulated hydrogen discs: the large holes discovered by the researchers.

It is therefore an important challenge for astrophysicists to optimise both the simulation codes and the models in such a way that – in conjunction with continually more powerful supercomputers – a self-consistent treatment of the dense interstellar medium can be achieved. Combined with improved supernova models, these future simulations will, hopefully, produce galaxies that match the real Universe even better than EAGLE does. However, the current study also demonstrates that EAGLE can already give valuable insight into the evolution of atomic hydrogen in galaxies. In a follow-up project, the researchers will examine the formation of the simulated galaxies to find out how and why some of them got so much more hydrogen than others.

 

Author: Bahe, Yannick

Email: ybahe@mpa-garching.mpg.de

Source: Max Planck Institute for Astrophysics