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Ubiquitous velocity fluctuations throughout the molecular interstellar medium


The density structure of the interstellar medium determines where stars form and release energy, momentum and heavy elements, driving galaxy evolution1,2,3,4. Density variations are seeded and amplified by gas motion, but the exact nature of this motion is unknown across spatial scales and galactic environments5. Although dense star-forming gas probably emerges from a combination of instabilities6,7, convergent flows8 and turbulence9, establishing the precise origin is challenging because it requires gas motion to be quantified over many orders of magnitude in spatial scale. Here we measure10,11,12 the motion of molecular gas in the Milky Way and in nearby galaxy NGC 4321, assembling observations that span a spatial dynamic range 10−1–103 pc. We detect ubiquitous velocity fluctuations across all spatial scales and galactic environments. Statistical analysis of these fluctuations indicates how star-forming gas is assembled. We discover oscillatory gas flows with wavelengths ranging from 0.3–400 pc. These flows are coupled to regularly spaced density enhancements that probably form via gravitational instabilities13,14. We also identify stochastic and scale-free velocity and density fluctuations, consistent with the structure generated in turbulent flows9. Our results demonstrate that the structure of the interstellar medium cannot be considered in isolation. Instead, its formation and evolution are controlled by nested, interdependent flows of matter covering many orders of magnitude in spatial scale.

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Fig. 1: Ubiquitous velocity fluctuations throughout the molecular ISM.
Fig. 2: Correlated density and velocity fluctuations.

Data availability

The 13CO (1−0) data of the Galactic Disk are from the Boston University-FCRAO GRS. The GRS data are publicly available at The Mopra data are publicly available at The ALMA HNCO 4(0,4) − 3(0,3) data of G0.253+0.016 are from project 2011.0.00217.S (principal investigator: J. Rathborne) and the raw data are publicly available through the ALMA archive ( All other data that support the findings of this study are available from the corresponding author on reasonable request. Source data are provided with this paper.

Code availability

SCOUSEPY and ACORNS, as well as the codes used for our statistical analyses, are freely available at GAUSSPY+ is available at Assistance with this software can be provided by the corresponding author.


  1. 1.

    McKee, C. F. & Ostriker, E. C. Theory of star formation. Annu. Rev. Astron. Astrophys. 45, 565–687 (2007).

    ADS  Google Scholar 

  2. 2.

    Zinnecker, H. & Yorke, H. W. Toward understanding massive star formation. Annu. Rev. Astron. Astrophys. 45, 481–563 (2007).

    ADS  Google Scholar 

  3. 3.

    Naab, T. & Ostriker, J. P. Theoretical challenges in galaxy formation. Annu. Rev. Astron. Astrophys. 55, 59–109 (2017).

    ADS  Google Scholar 

  4. 4.

    Kruijssen, J. M. D. et al. Fast and inefficient star formation due to short-lived molecular clouds and rapid feedback. Nature 569, 519–522 (2019).

    ADS  Google Scholar 

  5. 5.

    Dobbs, C. L. et al. in Protostars Planets VI (eds. H. Beuther et al.) 3–26 (Univ. of Arizona Press, 2014).

  6. 6.

    Elmegreen, B. G. & Elmegreen, D. M. Regular strings of H II regions and superclouds in spiral galaxies - clues to the origin of cloudy structure. Mon. Not. R. Astron. Soc. 203, 31–45 (1983).

    ADS  Google Scholar 

  7. 7.

    Kim, W.-T., Ostriker, E. C. & Stone, J. M. Magnetorotationally driven galactic turbulence and the formation of giant molecular clouds. Astrophys. J. 599, 1157–1172 (2003).

    ADS  Google Scholar 

  8. 8.

    Vázquez-Semadeni, E., Palau, A., Ballesteros-Paredes, J., Gómez, G. C. & Zamora-Avilés, M. Global hierarchical collapse in molecular clouds. towards a comprehensive scenario. Mon. Not. R. Astron. Soc. 490, 3061–3097 (2019).

    ADS  Google Scholar 

  9. 9.

    Padoan, P. et al. in Protostars Planets VI (eds. H. Beuther et al.) 77–100 (Univ. of Arizona Press, 2014).

  10. 10.

    Henshaw, J. D. et al. Molecular gas kinematics within the central 250 pc of the Milky Way. Mon. Not. R. Astron. Soc. 457, 2675–2702 (2016).

    ADS  Google Scholar 

  11. 11.

    Henshaw, J. D. et al. ‘The Brick’ is not a brick: a comprehensive study of the structure and dynamics of the central molecular zone cloud G0.253+0.016. Mon. Not. R. Astron. Soc. 485, 2457–2485 (2019).

    ADS  Google Scholar 

  12. 12.

    Riener, M. et al. GAUSSPY.: A fully automated Gaussian decomposition package for emission line spectra. Astron. Astrophys. 628, A78 (2019).

    Google Scholar 

  13. 13.

    Henshaw, J. D., Longmore, S. N. & Kruijssen, J. M. D. Seeding the galactic centre gas stream: gravitational instabilities set the initial conditions for the formation of protocluster clouds. Mon. Not. R. Astron. Soc. 463, L122–L126 (2016).

    ADS  Google Scholar 

  14. 14.

    Elmegreen, B. G., Elmegreen, D. M. & Efremov, Y. N. Regularly spaced infrared peaks in the dusty spirals of messier 100. Astrophys. J. 863, 59 (2018).

    ADS  Google Scholar 

  15. 15.

    Jackson, J. M. et al. The boston university-five college radio astronomy observatory galactic ring survey. Astrophys. J. Suppl. 163, 145–159 (2006).

    ADS  Google Scholar 

  16. 16.

    Jones, P. A. et al. Spectral imaging of the central molecular zone in multiple 3-mm molecular lines. Mon. Not. R. Astron. Soc. 419, 2961–2986 (2012).

    ADS  Google Scholar 

  17. 17.

    Henshaw, J. D., Caselli, P., Fontani, F., Jiménez-Serra, I. & Tan, J. C. The dynamical properties of dense filaments in the infrared dark cloud G035.39-00.33. Mon. Not. R. Astron. Soc. 440, 2860–2881 (2014).

    ADS  Google Scholar 

  18. 18.

    Klessen, R. S. & Hennebelle, P. Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks. Astron. Astrophys. 520, A17 (2010).

    ADS  Google Scholar 

  19. 19.

    Tafalla, M. & Hacar, A. Chains of dense cores in the taurus L1495/B213 complex. Astron. Astrophys. 574, A104 (2015).

    ADS  Google Scholar 

  20. 20.

    Lang, P. et al. PHANGS CO kinematics: disk orientations and rotation curves at 150 pc resolution. Astrophys. J. (in the press).

  21. 21.

    Elmegreen, B. G., Elmegreen, D. M. & Seiden, P. E. Spiral-arm amplitude variations and pattern speeds in the grand design galaxies M51, M81, and M100. Astrophys. J. 343, 602–607 (1989).

    ADS  Google Scholar 

  22. 22.

    Meidt, S. E. et al. Gas kinematics on giant molecular cloud scales in M51 with PAWS: cloud stabilization through dynamical pressure. Astrophys. J. 779, 45 (2013).

    ADS  Google Scholar 

  23. 23.

    Heyer, M. & Dame, T. M. Molecular clouds in the Milky Way. Annu. Rev. Astron. Astrophys. 53, 583–629 (2015).

    ADS  Google Scholar 

  24. 24.

    Larson, R. B. Turbulence and star formation in molecular clouds. Mon. Not. R. Astron. Soc. 194, 809–826 (1981).

    ADS  Google Scholar 

  25. 25.

    André, P. et al. in Protostars Planets VI (eds. H. Beuther et al.) 27–51 (Univ. of Arizona Press, 2014).

  26. 26.

    Henshaw, J. D. et al. Investigating the structure and fragmentation of a highly filamentary IRDC. Mon. Not. R. Astron. Soc. 463, 146–169 (2016).

    ADS  Google Scholar 

  27. 27.

    Misugi, Y., Inutsuka, S.-i & Arzoumanian, D. An origin for the angular momentum of molecular cloud cores: a prediction from filament fragmentation. Astrophys. J. 881, 11 (2019).

    ADS  Google Scholar 

  28. 28.

    Schneider, S. & Elmegreen, B. G. A catalog of dark globular filaments. Astrophys. J. Suppl. 41, 87–95 (1979).

    ADS  Google Scholar 

  29. 29.

    Elmegreen, B. G. Supercloud formation by gravitational collapse of magnetic gas in the crest of a spiral density wave. Astrophys. J. 433, 39–47 (1994).

    ADS  Google Scholar 

  30. 30.

    Nagasawa, M. Gravitational instability of the isothermal gas cylinder with an axial magnetic field. Progr. Theor. Phys. 77, 635–652 (1987).

    ADS  Google Scholar 

  31. 31.

    Inutsuka, S.-I. & Miyama, S. M. Self-similar solutions and the stability of collapsing isothermal filaments. Astrophys. J. 388, 392–399 (1992).

    ADS  Google Scholar 

  32. 32.

    de Vaucouleurs, G. et al. Third Reference Catalogue of Bright Galaxies (Springer, 1991).

  33. 33.

    Elmegreen, D. M. et al. Grand design and flocculent spirals in the Spitzer survey of stellar structure in galaxies (S4G). Astrophys. J. 737, 32 (2011).

    ADS  Google Scholar 

  34. 34.

    Knapen, J. H., Beckman, J. E., Heller, C. H., Shlosman, I. & de Jong, R. S. The central region in M100: observations and modeling. Astrophys. J. 454, 623 (1995).

    ADS  Google Scholar 

  35. 35.

    Knapen, J. H., Beckman, J. E., Cepa, J. & Nakai, N. Molecular gas observations and enhanced massive star formation efficiencies in M100. Astron. Astrophys. 308, 27–39 (1996).

    ADS  Google Scholar 

  36. 36.

    Ragan, S. E. et al. Giant molecular filaments in the Milky Way. Astron. Astrophys. 568, A73 (2014).

    Google Scholar 

  37. 37.

    Goodman, A. A. et al. The bones of the Milky Way. Astrophys. J. 797, 53 (2014).

    ADS  Google Scholar 

  38. 38.

    Zucker, C., Battersby, C. & Goodman, A. The skeleton of the Milky Way. Astrophys. J. 815, 23 (2015).

    ADS  Google Scholar 

  39. 39.

    Abreu-Vicente, J. et al. Giant molecular filaments in the Milky Way. II: the fourth galactic quadrant. Astron. Astrophys. 590, A131 (2016).

    Google Scholar 

  40. 40.

    Zucker, C., Battersby, C. & Goodman, A. Physical properties of large-scale galactic filaments. Astrophys. J. 864, 153 (2018).

    ADS  Google Scholar 

  41. 41.

    Simon, R., Rathborne, J. M., Shah, R. Y., Jackson, J. M. & Chambers, E. T. The characterization and galactic distribution of infrared dark clouds. Astrophys. J. 653, 1325–1335 (2006).

    ADS  Google Scholar 

  42. 42.

    Kainulainen, J. & Tan, J. C. High-dynamic-range extinction mapping of infrared dark clouds: dependence of density variance with sonic Mach number in molecular clouds. Astron. Astrophys. 549, A53 (2013).

    ADS  Google Scholar 

  43. 43.

    Jiménez-Serra, I. et al. Parsec-scale SiO emission in an infrared dark cloud. Mon. Not. R. Astron. Soc. 406, 187–196 (2010).

    ADS  Google Scholar 

  44. 44.

    Nguyên Luong, Q. et al. The Herschel view of massive star formation in G035.39-00.33: dense and cold filament of W48 undergoing a mini-starburst. Astron. Astrophys. 535, A76 (2011).

    Google Scholar 

  45. 45.

    Henshaw, J. D. et al. Complex, quiescent kinematics in a highly filamentary infrared dark cloud. Mon. Not. R. Astron. Soc. 428, 3425–3442 (2013).

    ADS  Google Scholar 

  46. 46.

    Henshaw, J. D. et al. Unveiling the early-stage anatomy of a protocluster hub with ALMA. Mon. Not. R. Astron. Soc. 464, L31–L35 (2017).

    ADS  Google Scholar 

  47. 47.

    Jiménez-Serra, I. et al. Gas kinematics and excitation in the filamentary IRDC G035.39-00.33. Mon. Not. R. Astron. Soc. 439, 1996–2013 (2014).

    ADS  Google Scholar 

  48. 48.

    Sokolov, V. et al. Multicomponent kinematics in a massive filamentary infrared dark cloud. Astrophys. J. 872, 30 (2019).

    ADS  Google Scholar 

  49. 49.

    Ferrière, K., Gillard, W. & Jean, P. Spatial distribution of interstellar gas in the innermost 3 kpc of our galaxy. Astron. Astrophys. 467, 611–627 (2007).

    ADS  Google Scholar 

  50. 50.

    Longmore, S. N. et al. G0.253 + 0.016: a molecular cloud progenitor of an arches-like cluster. Astrophys. J. 746, 117 (2012).

    ADS  Google Scholar 

  51. 51.

    Longmore, S. N. et al. Variations in the galactic star formation rate and density thresholds for star formation. Mon. Not. R. Astron. Soc. 429, 987–1000 (2013).

    ADS  Google Scholar 

  52. 52.

    Mills, E. A. C. et al. The dense gas fraction in galactic center clouds. Astrophys. J. 868, 7 (2018).

    ADS  Google Scholar 

  53. 53.

    Ginsburg, A. et al. Dense gas in the galactic central molecular zone is warm and heated by turbulence. Astron. Astrophys. 586, A50 (2016).

    Google Scholar 

  54. 54.

    Krieger, N. et al. The survey of water and ammonia in the galactic center (swag): molecular cloud evolution in the central molecular zone. Astrophys. J. 850, 77 (2017).

    ADS  Google Scholar 

  55. 55.

    Shetty, R., Beaumont, C. N., Burton, M. G., Kelly, B. C. & Klessen, R. S. The linewidth-size relationship in the dense interstellar medium of the central molecular zone. Mon. Not. R. Astron. Soc. 425, 720–729 (2012).

    ADS  Google Scholar 

  56. 56.

    Clark, P. C., Glover, S. C. O., Ragan, S. E., Shetty, R. & Klessen, R. S. On the temperature structure of the galactic center cloud G0.253+0.016. Astrophys. J. Lett. 768, L34 (2013).

    ADS  Google Scholar 

  57. 57.

    Kruijssen, J. M. D. & Longmore, S. N. Comparing molecular gas across cosmic time-scales: the Milky Way as both a typical spiral galaxy and a high-redshift galaxy analogue. Mon. Not. R. Astron. Soc. 435, 2598–2603 (2013).

    ADS  Google Scholar 

  58. 58.

    Walker, D. L. et al. Star formation in a high-pressure environment: an SMA view of the galactic centre dust ridge. Mon. Not. R. Astron. Soc. 474, 2373–2388 (2018).

    ADS  Google Scholar 

  59. 59.

    Yusef-Zadeh, F., Muno, M., Wardle, M. & Lis, D. C. The origin of diffuse X-ray and γ-ray emission from the galactic center region: cosmic-ray particles. Astrophys. J. 656, 847–869 (2007).

    ADS  Google Scholar 

  60. 60.

    Sofue, Y. Galactic-center molecular arms, ring, and expanding shell. I: kinematical structures in longitude-velocity diagrams. Publ. Astron. Soc. Jpn 47, 527–549 (1995).

    ADS  Google Scholar 

  61. 61.

    Molinari, S. et al. A 100 pc elliptical and twisted ring of cold and dense molecular clouds revealed by Herschel around the galactic center. Astrophys. J. Lett. 735, L33 (2011).

    ADS  Google Scholar 

  62. 62.

    Kruijssen, J. M. D., Dale, J. E. & Longmore, S. N. The dynamical evolution of molecular clouds near the galactic centre. I: orbital structure and evolutionary timeline. Mon. Not. R. Astron. Soc. 447, 1059–1079 (2015).

    ADS  Google Scholar 

  63. 63.

    Kauffmann, J., Pillai, T. & Zhang, Q. The galactic center cloud G0.253.0.016: a massive dense cloud with low star formation potential. Astrophys. J. Lett. 765, L35 (2013).

    ADS  Google Scholar 

  64. 64.

    Rathborne, J. M. et al. A cluster in the making: ALMA reveals the initial conditions for high-mass cluster formation. Astrophys. J. 802, 125 (2015).

    ADS  Google Scholar 

  65. 65.

    Mills, E. A. C. et al. Abundant CH3 OH masers but no new evidence for star formation in GCM0.253+0.016. Astrophys. J. 805, 72 (2015).

    ADS  Google Scholar 

  66. 66.

    Rathborne, J. M. et al. G0.253+0.016: a centrally condensed, high-mass protocluster. Astrophys. J. 786, 140 (2014).

    ADS  Google Scholar 

  67. 67.

    Sun, J. et al. Cloud-scale molecular gas properties in 15 nearby galaxies. Astrophys. J. 860, 172 (2018).

    ADS  Google Scholar 

  68. 68.

    Tully, R. B. et al. The extragalactic distance database. Astron. J. 138, 323–331 (2009).

    ADS  Google Scholar 

  69. 69.

    Reid, M. J. et al. Trigonometric parallaxes of high mass star forming regions: the structure and kinematics of the Milky Way. Astrophys. J. 783, 130 (2014).

    ADS  Google Scholar 

  70. 70.

    Molinari, S. et al. Clouds, filaments, and protostars: the Herschel Hi-GAL Milky Way. Astron. Astrophys. 518, L100 (2010).

    ADS  Google Scholar 

  71. 71.

    Battersby, C. et al. Characterizing precursors to stellar clusters with Herschel. Astron. Astrophys. 535, A128 (2011).

    Google Scholar 

  72. 72.

    Mills, E. A. C. & Battersby, C. Origins of scatter in the relationship between HCN 1-0 and dense gas mass in the galactic center. Astrophys. J. 835, 76 (2017).

    ADS  Google Scholar 

  73. 73.

    Foster, J. B. et al. The Millimetre Astronomy Legacy Team 90 GHz (MALT90) pilot survey. Astrophys. J. Suppl. 197, 25 (2011).

    ADS  Google Scholar 

  74. 74.

    Jackson, J. M. et al. MALT90: the Millimetre Astronomy Legacy Team 90 GHz survey. Publ. Astron. Soc. Aus. 30, e057 (2013).

    ADS  Google Scholar 

  75. 75.

    Riener, M. et al. Autonomous gaussian decomposition of the galactic ring survey. I: global statistics and properties of the 13CO emission data. Astron. Astrophys. 633, A14 (2020).

    Google Scholar 

  76. 76.

    Pagani, L., Daniel, F. & Dubernet, M. L. On the frequency of N2H+ and N2D+. Astron. Astrophys. 494, 719–727 (2009).

    ADS  Google Scholar 

  77. 77.

    Burton, W. B. On the kinematic distribution of galactic neutral hydrogen. Astron. Astrophys. 19, 51–65 (1972).

    ADS  Google Scholar 

  78. 78.

    Lazarian, A. & Pogosyan, D. Velocity modification of H I power spectrum. Astrophys. J. 537, 720–748 (2000).

    ADS  Google Scholar 

  79. 79.

    Ostriker, E. C., Stone, J. M. & Gammie, C. F. Density, velocity, and magnetic field structure in turbulent molecular cloud models. Astrophys. J. 546, 980–1005 (2001).

    ADS  Google Scholar 

  80. 80.

    Beaumont, C., Goodman, A. & Greenfield, P. in Astronomical Data Analysis Software and Systems XXIV (eds Taylor, A. R. & Rosolowsky, E.) 101–110 (Astronomical Society of the Pacific, 2015).

  81. 81.

    Robitaille, T., Beaumont, C., Qian, P., Borkin, M. & Goodman, A. glueviz v0.13.1: multidimensional data exploration (2017);

  82. 82.

    Reid, M. J. et al. Trigonometric parallaxes of high-mass star-forming regions: our view of the Milky Way. Astrophys. J. 885, 131 (2019).

    ADS  Google Scholar 

  83. 83.

    Clarke, S. D. et al. Synthetic C 18O observations of fibrous filaments: the problems of mapping from PPV to PPP. Mon. Not. R. Astron. Soc 479, 1722–1746 (2018).

    ADS  Google Scholar 

  84. 84.

    Langer, W. D., Velusamy, T., Morris, M. R., Goldsmith, P. F. & Pineda, J. L. Kinematics and properties of the central molecular zone as probed with [C II]. Astron. Astrophys. 599, A136 (2017).

    ADS  Google Scholar 

  85. 85.

    Longmore, S. N. et al. H2O southern galactic plane survey (HOPS): paper III—properties of dense molecular gas across the inner Milky Way. Mon. Not. R. Astron. Soc. 470, 1462–1490 (2017).

    ADS  Google Scholar 

  86. 86.

    Koch, E. W. & Rosolowsky, E. W. Filament identification through mathematical morphology. Mon. Not. R. Astron. Soc. 452, 3435–3450 (2015).

    ADS  Google Scholar 

  87. 87.

    Ossenkopf, V. & MacLow, M. M. Turbulent velocity structure in molecular clouds. Astron. Astrophys. 390, 307–326 (2002).

    ADS  Google Scholar 

  88. 88.

    Koch, E. W. et al. Spatial power spectra of dust across the local group: no constraint on disc scale height. Mon. Not. R. Astron. Soc. 492, 2663–2682 (2020).

    ADS  Google Scholar 

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We thank T. Müller from the Max Planck Institut für Astronomie for assisting with the data visualization and production of the Supplementary Videos. We thank J. Rathborne for making the data on G0.253+0.016 available, and P. Caselli, B. Elmegreen and J. Soler for discussions. J.M.D.K. and M.C. acknowledge funding from the German Research Foundation (DFG) in the form of an Emmy Noether Research Group grant (number KR4801/1-1) and DFG Sachbeihilfe grant (number KR4801/2-1). J.M.D.K. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme via the ERC Starting Grant MUSTANG (grant agreement number 714907). M.R. and J.K. acknowledge funding from the European Union’s Horizon 2020 research and innovation program under grant agreement number 639459 (PROMISE). The work of A.K.L. and J.S. is partially supported by the National Science Foundation (NSF) under grant numbers 1615105, 1615109 and 1653300, and by NASA under ADAP grant numbers NNX16AF48G and NNX17AF39G. E.R. acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC) under funding reference number RGPIN-2017-03987. C.B. acknowledges support from the NSF under grant number 1816715. R.S.K. and S.C.O.G. acknowledge funding from the Deutsche Forschungsgemeinschaft (DFG) via the Collaborative Research Center (SFB 881 The Milky Way System; subprojects A1, B1, and B2) and from the Heidelberg Cluster of Excellence STRUCTURES in the framework of Germany’s Excellence Strategy (grant number EXC-2181/1-390900948). E.S. acknowledges funding from the ERC under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 694343). F.B. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme (grant agreement number 726384). J.P. acknowledges funding from the Programme National ‘Physique et Chimie du Milieu Interstellaire’ (PCMI) of CNRS/INSU with INC/INP, co-funded by CEA and CNES. The GRS is a joint project of Boston University and Five College Radio Astronomy Observatory, funded by the NSF under grant numbers AST-9800334, AST-0098562, AST-0100793, AST-0228993 and AST-0507657. The N2H+ (1−0) data of the CMZ was obtained using the Mopra radio telescope, a part of the Australia Telescope National Facility which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. The University of New South Wales (UNSW) digital filter bank (the UNSW-MOPS) used for the observations with Mopra was provided with support from the Australian Research Council (ARC), UNSW, Sydney and Monash Universities, as well as CSIRO.

Author information




J.D.H., J.M.D.K. and S.N.L. were responsible for the experiment design. J.D.H. led the project, carried out the experiment, developed the analysis methods, interpreted the results and wrote the text, to which J.M.D.K, S.N.L. and M.R. contributed. E.R. created the mock datasets and designed the observational estimator 2D model test. J.D.H. and M.R. were responsible for data visualization. Supplementary Videos 1–5 were coproduced by J.D.H. Supplementary Videos 610 were produced by M.R. J.D.H. performed the spectral decomposition for all regions except for the GRS data for which M.R. was responsible. All authors contributed to aspects of the data reduction and analysis, the interpretation of the results, and the writing of the manuscript.

Corresponding author

Correspondence to Jonathan D. Henshaw.

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The authors declare no competing interests.

Additional information

Peer review information Nature Astronomy thanks Mark Heyer and Alex Lazarian for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Summary of the observations.

Here we highlight the observations and region selection for the data presented in Figure 1. The scales probed by our Galactic disc selection (seen in square brackets) are relevant for a distance of 3 kpc. Out of each of these environments we select sub-regions for the statistical analysis presented in Fig. 2 (see Statistical analysis of the observational data).

Extended Data Fig. 2 Maps of the regions selected for statistical analysis.

The upper panels display our galactic disc environments. From left to right we show part of the main southern spiral arm in NGC 4321 (a), a GMC in the Galactic disc (b), and an individual filament located within that same GMC (c). The bottom panels display our selected regions in the CMZ: The series of molecular clouds investigated by ref. 13 (d) and an individual GMC located within the CMZ gas stream (e). The cyan points in panel ‘a’ refer to the locations of star forming complexes identified in the mid-infrared14. In the upper left of each panel we indicate the tracer used to create each image. Scale bars are included in the bottom right corner of each image. These regions correspond to the areas over which we perform our statistical analysis (see Statistical analysis of the observational data and Fig. 2).

Extended Data Fig. 3 Distribution of our density proxy (top) and velocity centroids (bottom) along the crest of the structures displaying periodicity.

From left to right we show distance along the crest of each structure versus mean density (top) and velocity (bottom), for our selected regions in NGC 4321 (a, b), the CMZ (c, d), and IRDC G035.39-00.33 (e, f), respectively (see Extended Data Fig. 2). The coloured shaded region in each panel represents the standard deviation of the data measured orthogonal to the crest. Source data

Extended Data Fig. 4 A comparison between our density proxy and the line-of-sight velocity differential.

Here we show the profile of our density proxy (coloured lines) with the normalised velocity differential (black line) along the crests of our our selected regions in NGC 4321 (a), the CMZ (b), and IRDC G035.39-00.33 (c), respectively. Note that in panel ‘b’ we show emission of N2H+ (1-0) rather than the column density distribution displayed in Extended Data Fig. 3c (see the discussion in the Supplementary Information). The black dotted line highlights where the derivative of the velocity is 0.0 kms−1 pc−1.

Supplementary information

Supplementary Information

Supplementary Figs. 1– 6, models and discussion.

Supplementary Video 1

Ubiquitous velocity fluctuations throughout the molecular interstellar medium. Here we show a movie highlighting the p-p-v structure of NGC4321. The data points are equivalent to those presented in Fig. 1a.

Supplementary Video 2

Equivalent to Supplementary Video 1, but for the Galactic Disk.

Supplementary Video 3

Equivalent to Supplementary Video 1, but for the G035.39-00.33.

Supplementary Video 4

Equivalent to Supplementary Video 1, but for the CMZ.

Supplementary Video 5

Equivalent to Supplementary Video 1, but for G0.253+0.016.

Supplementary Video 6

A movie highlighting the velocity fluctuations throughout NGC4321. Here we show the position-velocity location of data extracted using our spectral decomposition method for individual slices through the other position axis.

Supplementary Video 7

Equivalent to Supplementary Video 6, but for the Galactic disc. Here we show the full decomposition of the GRS data set and not just the region displayed in Fig. 1b and in Supplementary Video 2. This demonstrates that the velocity fluctuations are detected throughout the entire area covered by the GRS survey.

Supplementary Video 8

Equivalent to Supplementary Video 6, but for G035.39-00.33.

Supplementary Video 9

Equivalent to Supplementary Video 6, but for the CMZ.

Supplementary Video 10

Equivalent to Supplementary Video 6, but for G0.253+0.016.

Source data

Source Data Fig. 2

Source data for Fig. 2.

Source Data Extended Data Fig. 3

Source data for Extended Data Fig. 3.

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Henshaw, J.D., Kruijssen, J.M.D., Longmore, S.N. et al. Ubiquitous velocity fluctuations throughout the molecular interstellar medium. Nat Astron 4, 1064–1071 (2020).

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Further reading

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