Montage of the NOEMA Telescopes and the detected massive disk galaxies with spiral arms and bars that actively transported cold gas inward. © Jean-Baptiste Jolly
Spiral Arms and Bars Drive Gas Transport at Cosmic Noon
Studies from the Infrared & Submillimeter Astronomy Group at the Max Planck Institute for Extraterrestrial Physics (MPE) using NOEMA and JWST reveal that during cosmic noon, massive disk galaxies with spiral arms and bars actively transported cold gas inward. This process sustained star formation by distributing gas efficiently across galactic disks, challenging previous views of early chaotic galaxies.
Galaxies need a continuous supply of cold gas to form new stars. This was especially true during "cosmic noon", roughly 8 to 10 billion years ago, when galaxies across the universe were forming stars at rates far exceeding those seen today. A key question in galaxy evolution is therefore how this gas was distributed within galaxies, and how it was transported from the outer disk into the regions where stars, bulges, and central black holes form and grow. Two new studies from the NOEMA3D survey, led by the Infrared-Submillimeter-Astronomy Group at the Max Planck Institute for Extraterrestrial Physics (MPE) and collaborators, now provide one of the clearest observational views yet of these processes.
Using the NOrthern Extended Millimeter Array (NOEMA), a radio interferometer located in the French Alps, the team obtained the deepest millimeter-wave observations to date of cold molecular gas — traced via CO emission — in ten massive, star-forming galaxies at redshifts z ~ 1.1–1.6. With integration times of typically more than 20 hours per galaxy, the NOEMA3D survey resolves both the distribution and kinematics of molecular gas on kiloparsec scales. These observations were combined with high-resolution infrared imaging from the James Webb Space Telescope (JWST), which reveals the underlying stellar structure of the same galaxies in unprecedented detail.
What JWST shows is itself striking: many of these distant systems are not the chaotic, merger-dominated objects that early galaxies were long assumed to be. Instead, they are well-ordered disk galaxies with clear spiral arms and, in four out of ten cases, bars. Structural features previously thought to be rare or absent at these redshifts.
Galaxies need a continuous supply of cold gas to form new stars. This was especially true during "cosmic noon", roughly 8 to 10 billion years ago, when galaxies across the universe were forming stars at rates far exceeding those seen today. A key question in galaxy evolution is therefore how this gas was distributed within galaxies, and how it was transported from the outer disk into the regions where stars, bulges, and central black holes form and grow. Two new studies from the NOEMA3D survey, led by the Infrared-Submillimeter-Astronomy Group at the Max Planck Institute for Extraterrestrial Physics (MPE) and collaborators, now provide one of the clearest observational views yet of these processes.
Using the NOrthern Extended Millimeter Array (NOEMA), a radio interferometer located in the French Alps, the team obtained the deepest millimeter-wave observations to date of cold molecular gas — traced via CO emission — in ten massive, star-forming galaxies at redshifts z ~ 1.1–1.6. With integration times of typically more than 20 hours per galaxy, the NOEMA3D survey resolves both the distribution and kinematics of molecular gas on kiloparsec scales. These observations were combined with high-resolution infrared imaging from the James Webb Space Telescope (JWST), which reveals the underlying stellar structure of the same galaxies in unprecedented detail.
What JWST shows is itself striking: many of these distant systems are not the chaotic, merger-dominated objects that early galaxies were long assumed to be. Instead, they are well-ordered disk galaxies with clear spiral arms and, in four out of ten cases, bars. Structural features previously thought to be rare or absent at these redshifts.
G4_38065 is a massive spiral galaxy at z = 1.12. The velocity residuals, obtained by subtracting a model velocity map from the observed one, show clear patterns along the spiral arms which we interpret as inflowing gas refueling the galaxy. © Jean-Baptiste Jolly
Cold Gas Distribution Supports Star Formation Across Galactic Disks
The first study analyzes the kinematics of the molecular gas. All ten galaxies show ordered rotation consistent with a rotating disk. But after subtracting the best-fitting disk model, coherent velocity residuals remain in nearly every system, gas motions that cannot be accounted for by simple rotation alone. These residuals reach typical in-plane velocities of 50 to 100 km/s, substantially larger than comparable non-circular motions in nearby disk galaxies. Crucially, they are spatially correlated with the non-axisymmetric structures seen in the JWST images: spiral arms and bars. “For the first time, we can directly link spiral arms and bars to the motions of cold gas within galaxies,” says Jean-Baptiste Jolly. “This provides compelling evidence that these structures were already driving gas transport when the Universe was at the peak of its star-forming activity.”.
Spiral arms and bars are therefore not merely aesthetic features in galaxy images. They are dynamical structures that actively redistribute gas within the disk. When interpreted as radial inflows, the inferred molecular gas transport rates are often comparable to the galaxies' star formation rates, of order tens of solar masses per year. Such flows could move gas inward to feed central star formation, contribute to the growth of bulges, and potentially supply material to central supermassive black holes.
The companion study examines where the cold gas and dust are actually located. Comparing the spatial distributions of CO emission, neutral carbon [C I], dust continuum, stars, and star formation across the same ten galaxies, it finds that molecular gas and dust are generally extended over the full galactic disk, with sizes broadly comparable to the stellar component. This stands in sharp contrast to merger-driven compact starburst galaxies at similar redshifts, where dust and star formation are typically concentrated in small central regions. The resolved measurements further show that both the molecular gas fraction and the gas depletion time remain broadly flat across the disk, out to approximately twice the stellar effective radius. “The depth of the NOEMA observations allows us to trace the cold-gas reservoirs that fueled galaxy growth during cosmic noon,” says Jianhang Chen. “We can now see, in unprecedented detail, how galaxies sustained star formation across their disks over billions of years.”
Taken together, the two studies present a coherent picture of how massive disk galaxies sustained their star formation during a crucial epoch in cosmic history. Gas was present across the full disk; star formation proceeded with broadly similar efficiency at different radii. Internal structures, like spiral arms and bars, provided an efficient mechanism for moving gas inward. The NOEMA3D observations thereby connect the large-scale gas reservoirs of galaxies to the internal dynamical processes that regulate their growth.
These results also highlight the power of combining NOEMA and JWST. NOEMA provides the cold-gas kinematics and molecular gas maps; JWST reveals the stellar structures that shape the gas motion. Only by combining both telescopes can the link between morphology and gas dynamics be directly observed.
The broader implication is significant. By z ~ 1–2, massive star-forming galaxies already possessed organized disks with spiral arms and bars capable of driving significant gas transport. These structures likely played an important role in keeping galaxies on the star-forming main sequence and in shaping the buildup of disks, bulges, and black holes over cosmic time. The findings challenge the long-held view that early galaxies were predominantly turbulent and merger-driven. Many were already mature, well-ordered systems — not unlike our own Milky Way, but younger and considerably more active.
Spiral arms and bars are therefore not merely aesthetic features in galaxy images. They are dynamical structures that actively redistribute gas within the disk. When interpreted as radial inflows, the inferred molecular gas transport rates are often comparable to the galaxies' star formation rates, of order tens of solar masses per year. Such flows could move gas inward to feed central star formation, contribute to the growth of bulges, and potentially supply material to central supermassive black holes.
The companion study examines where the cold gas and dust are actually located. Comparing the spatial distributions of CO emission, neutral carbon [C I], dust continuum, stars, and star formation across the same ten galaxies, it finds that molecular gas and dust are generally extended over the full galactic disk, with sizes broadly comparable to the stellar component. This stands in sharp contrast to merger-driven compact starburst galaxies at similar redshifts, where dust and star formation are typically concentrated in small central regions. The resolved measurements further show that both the molecular gas fraction and the gas depletion time remain broadly flat across the disk, out to approximately twice the stellar effective radius. “The depth of the NOEMA observations allows us to trace the cold-gas reservoirs that fueled galaxy growth during cosmic noon,” says Jianhang Chen. “We can now see, in unprecedented detail, how galaxies sustained star formation across their disks over billions of years.”
Taken together, the two studies present a coherent picture of how massive disk galaxies sustained their star formation during a crucial epoch in cosmic history. Gas was present across the full disk; star formation proceeded with broadly similar efficiency at different radii. Internal structures, like spiral arms and bars, provided an efficient mechanism for moving gas inward. The NOEMA3D observations thereby connect the large-scale gas reservoirs of galaxies to the internal dynamical processes that regulate their growth.
These results also highlight the power of combining NOEMA and JWST. NOEMA provides the cold-gas kinematics and molecular gas maps; JWST reveals the stellar structures that shape the gas motion. Only by combining both telescopes can the link between morphology and gas dynamics be directly observed.
The broader implication is significant. By z ~ 1–2, massive star-forming galaxies already possessed organized disks with spiral arms and bars capable of driving significant gas transport. These structures likely played an important role in keeping galaxies on the star-forming main sequence and in shaping the buildup of disks, bulges, and black holes over cosmic time. The findings challenge the long-held view that early galaxies were predominantly turbulent and merger-driven. Many were already mature, well-ordered systems — not unlike our own Milky Way, but younger and considerably more active.
Contacts:
Dr. Jean-Baptiste Jolly
Postdoc Infrared-Group
Tel: +49 89 30000-3335
Email: jbjolly@mpe.mpg.de
Max-Planck-Institut für extraterrestrische Physik, Garching
Dr. Jianhang Chen
Postdoc Infrared-Group
Tel: +49 89 30000-3374
Email: jhchen@mpe.mpg.de
Max-Planck-Institut für extraterrestrische Physik, Garching
Original Publication
1. Chen, J., L. Tacconi, R. Genzel, R. Neri, K. Schuster, N. Förster Schreiber, J.-B. Jolly et al.
NOEMA3D: Spatially resolved dust, CO, and [C I] in massive star-forming main sequence galaxies at cosmic noon
A & A
DOI
2. Jolly, J.-B., L.J. Tacconi, R. Genzel, R. Neri, K. Schuster, J. Chen et al.
NOEMA3D: Resolving radial gas flows in disk galaxies at z ∼ 1.1 − 1.6 with high-resolution CO observations
A & A
Source | DOI
Further Information
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