Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

The gravitationally unstable gas disk of a starburst galaxy 12 billion years ago


Galaxies in the early Universe that are bright at submillimetre wavelengths (submillimetre-bright galaxies) are forming stars at a rate roughly 1,000 times higher than the Milky Way. A large fraction of the new stars form in the central kiloparsec of the galaxy1,2,3, a region that is comparable in size to the massive, quiescent galaxies found at the peak of cosmic star-formation history4 and the cores of present-day giant elliptical galaxies. The physical and kinematic properties inside these compact starburst cores are poorly understood because probing them at relevant spatial scales requires extremely high angular resolution. Here we report observations with a linear resolution of 550 parsecs of gas and dust in an unlensed, submillimetre-bright galaxy at a redshift of z = 4.3, when the Universe was less than two billion years old. We resolve the spatial and kinematic structure of the molecular gas inside the heavily dust-obscured core and show that the underlying gas disk is clumpy and rotationally supported (that is, its rotation velocity is larger than the velocity dispersion). Our analysis of the molecular gas mass per unit area suggests that the starburst disk is gravitationally unstable, which implies that the self-gravity of the gas is stronger than the differential rotation of the disk and the internal pressure due to stellar-radiation feedback. As a result of the gravitational instability in the disk, the molecular gas would be consumed by star formation on a timescale of 100 million years, which is comparable to gas depletion times in merging starburst galaxies5.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: CO morphology and kinematics of AzTEC-1.
Fig. 2: Spectra and maps of the two large clumps.
Fig. 3: Radially averaged Toomre Q parameter.
Fig. 4: Pixel-to-pixel variations in the physical properties.


  1. 1.

    Swinbank, A. M. et al. Intense star formation within resolved compact regions in a galaxy at z = 2.3. Nature 464, 733–736 (2010).

    ADS  Article  PubMed  CAS  Google Scholar 

  2. 2.

    Ikarashi, S. et al. Compact starbursts in z ~ 3–6 submillimeter galaxies revealed by ALMA. Astrophys. J. 810, 133 (2015).

    ADS  Article  CAS  Google Scholar 

  3. 3.

    Simpson, J. M. et al. The SCUBA-2 cosmology legacy survey: ALMA resolves the rest-frame far-infrared emission of sub-millimeter galaxies. Astrophys. J. 799, 81 (2015).

    ADS  Article  CAS  Google Scholar 

  4. 4.

    van Dokkum, P. et al. Forming compact massive galaxies. Astrophys. J. 813, 23 (2015).

    ADS  Article  Google Scholar 

  5. 5.

    Kennicutt, R. C. Jr. The global Schmidt law in star-forming galaxies. Astrophys. J. 498, 541–552 (1998).

    ADS  Article  CAS  Google Scholar 

  6. 6.

    Hughes, D. H. et al. High-redshift star formation in the Hubble Deep Field revealed by a submillimetre-wavelength survey. Nature 394, 241–247 (1998).

    ADS  Article  CAS  Google Scholar 

  7. 7.

    Barger, A. J. et al. Submillimetre-wavelength detection of dusty star-forming galaxies at high redshift. Nature 394, 248–251 (1998).

    ADS  Article  CAS  Google Scholar 

  8. 8.

    Chapman, S. C. et al. A redshift survey of the submillimeter galaxy population. Astrophys. J. 622, 772–796 (2005).

    ADS  Article  CAS  Google Scholar 

  9. 9.

    Bothwell, M. S. et al. A survey of molecular gas in luminous sub-millimetre galaxies. Mon. Not. R. Astron. Soc. 429, 3047–3067 (2013).

    ADS  Article  CAS  Google Scholar 

  10. 10.

    Ivison, R. J. et al. Herschel-ATLAS: a binary HyLIRG pinpointing a cluster of starbursting protoellipticals. Astrophys. J. 772, 137 (2013).

    ADS  Article  CAS  Google Scholar 

  11. 11.

    Tacconi, L. J. et al. Submillimeter galaxies at z ~ 2: evidence for major mergers and constraints on lifetimes, IMF, and CO-H2 conversion factor. Astrophys. J. 680, 246–262 (2008).

    ADS  Article  CAS  Google Scholar 

  12. 12.

    Hodge, J. A. et al. Evidence for a clumpy, rotating gas disk in a submillimeter galaxy at z = 4. Astrophys. J. 760, 11 (2012).

    ADS  Article  CAS  Google Scholar 

  13. 13.

    Iono, D. et al. Clumpy and extended starbursts in the brightest unlensed submillimeter galaxies. Astrophys. J. 829, L10 (2016).

    ADS  Article  Google Scholar 

  14. 14.

    Tadaki, K.-i. et al. Bulge-forming galaxies with an extended rotating disk at z ~ 2. Astrophys. J. 834, 135 (2017).

    ADS  Article  CAS  Google Scholar 

  15. 15.

    Swinbank, A. M. et al. ALMA resolves the properties of star-forming regions in a dense gas disk at z ~ 3. Astrophys. J. 806, L17 (2015).

    ADS  Article  CAS  Google Scholar 

  16. 16.

    Sharda, P. et al. Testing star formation laws in a starburst galaxy at redshift 3 resolved with ALMA. Mon. Not. R. Astron. Soc. 477, 4380–4390 (2018).

    ADS  Article  Google Scholar 

  17. 17.

    Bolatto, A. D. et al. The resolved properties of extragalactic giant molecular clouds. Astrophys. J. 686, 948–965 (2008).

    ADS  Article  CAS  Google Scholar 

  18. 18.

    Cappellari, M. Structure and kinematics of early-type galaxies from integral field spectroscopy. Annu. Rev. Astron. Astrophys. 54, 597–665 (2016).

    ADS  Article  CAS  Google Scholar 

  19. 19.

    Veale, M. et al. The MASSIVE survey – V. Spatially resolved stellar angular momentum, velocity dispersion, and higher moments of the 41 most massive local early-type galaxies. Mon. Not. R. Astron. Soc. 464, 356–384 (2017).

    ADS  Article  Google Scholar 

  20. 20.

    Naab, T. et al. The ATLAS3D project – XXV. Two-dimensional kinematic analysis of simulated galaxies and the cosmological origin of fast and slow rotators. Mon. Not. R. Astron. Soc. 444, 3357–3387 (2014).

    ADS  Article  CAS  Google Scholar 

  21. 21.

    Genzel, R. et al. The Sins survey of z ~ 2 galaxy kinematics: properties of the giant star-forming clumps. Astrophys. J. 733, 101 (2011).

    ADS  Article  CAS  Google Scholar 

  22. 22.

    Bournaud, F. et al. The long lives of giant clumps and the birth of outflows in gas-rich galaxies at high-redshift. Astrophys. J. 780, 57–75 (2014).

    ADS  Article  CAS  Google Scholar 

  23. 23.

    Mandelker, N. et al. The population of giant clumps in simulated high-z galaxies: in situ and ex situ migration and survival. Mon. Not. R. Astron. Soc. 443, 3675–3702 (2014).

    ADS  Article  Google Scholar 

  24. 24.

    Genzel, R. et al. The SINS/zC-SINF survey of z ~ 2 galaxy kinematics: evidence for gravitational quenching. Astrophys. J. 785, 75 (2014).

    ADS  Article  CAS  Google Scholar 

  25. 25.

    Thompson, T. et al. Radiation pressure-supported starburst disks and active galactic nucleus fueling. Astrophys. J. 630, 167–185 (2005).

    ADS  Article  Google Scholar 

  26. 26.

    Cacciato, M. et al. Evolution of violent gravitational disc instability in galaxies: late stabilization by transition from gas to stellar dominance. Mon. Not. R. Astron. Soc. 421, 818–831 (2012).

    ADS  Google Scholar 

  27. 27.

    Tacconi, L. J. et al. Phibss: molecular gas content and scaling relations in z ~ 1–3 massive, main-sequence star-forming galaxies. Astrophys. J. 768, 74 (2013).

    ADS  Article  CAS  Google Scholar 

  28. 28.

    Narayanan, D. et al. The star-forming molecular gas in high-redshift submillimetre galaxies. Mon. Not. R. Astron. Soc. 400, 1919–1935 (2009).

    ADS  Article  Google Scholar 

  29. 29.

    Ueda, J. et al. Cold molecular gas in merger remnants. I. Formation of molecular gas disks. Astrophys. J. Suppl. Ser. 214, 1 (2014).

    ADS  Article  CAS  Google Scholar 

  30. 30.

    Dekel, A. et al. Cold streams in early massive hot haloes as the main mode of galaxy formation. Nature 457, 451–454 (2009).

    ADS  Article  PubMed  CAS  Google Scholar 

  31. 31.

    Scott, K. B. et al. AzTEC millimetre survey of the COSMOS field – I. Data reduction and source catalogue. Mon. Not. R. Astron. Soc. 385, 2225–2238 (2008).

    ADS  Article  Google Scholar 

  32. 32.

    Yun, M. S. et al. Early science with the Large Millimeter Telescope: CO and [C ii] emission in the z = 4.3 AzTEC J095942.9+022938 (COSMOS AzTEC-1). Mon. Not. R. Astron. Soc. 454, 3485–3499 (2015).

    ADS  Article  CAS  Google Scholar 

  33. 33.

    Toft, S. et al. Submillimeter galaxies as progenitors of compact quiescent galaxies. Astrophys. J. 782, 68 (2014).

    ADS  Article  Google Scholar 

  34. 34.

    Chabrier, G. The galactic disk mass function: reconciliation of the Hubble Space Telescope and nearby determinations. Astrophys. J. 586, L133–L136 (2003).

    ADS  Article  CAS  Google Scholar 

  35. 35.

    McMullin, J. P., Waters, B., Schiebel, D., Young, W. & Golap, K. CASA architecture and applications. ASP Conf. Ser. 376, 127–130 (2007).

    ADS  Google Scholar 

  36. 36.

    Smolčić, V. et al. The redshift and nature of AzTEC/COSMOS 1: a starburst galaxy at z = 4.6. Astrophys. J. 731, L27 (2011).

    ADS  Article  CAS  Google Scholar 

  37. 37.

    Laigle, C. et al. The COSMOS2015 catalog: exploring the 1 < z < 6 universe with half a million galaxies. Astrophys. J. Suppl. Ser. 24, 224 (2016).

    Google Scholar 

  38. 38.

    Roseboom, I. G. et al. The Herschel multi-tiered extragalactic survey: SPIRE-mm photometric redshifts. Mon. Not. R. Astron. Soc. 419, 2758–2773 (2012).

    ADS  Article  Google Scholar 

  39. 39.

    Oliver, S. J. et al. The Herschel multi-tiered extragalactic survey: HerMES. Mon. Not. R. Astron. Soc. 424, 1614–1635 (2012).

    ADS  Article  Google Scholar 

  40. 40.

    Smolčić, V. et al. The VLA-COSMOS 3 GHz large project: continuum data and source catalog release. Astron. Astrophys. 602, A1 (2017).

    Article  CAS  Google Scholar 

  41. 41.

    da Cunha, E., Charlot, S. & Elbaz, D. A simple model to interpret the ultraviolet, optical and infrared emission from galaxies. Mon. Not. R. Astron. Soc. 388, 1595–1617 (2008).

    ADS  Article  CAS  Google Scholar 

  42. 42.

    da Cunha, E. et al. An ALMA survey of sub-millimeter galaxies in the extended Chandra deep field south: physical properties derived from ultraviolet-to-radio modeling. Astrophys. J. 806, 110 (2015).

    ADS  Article  CAS  Google Scholar 

  43. 43.

    Bruzual, G. & Charlot, S. Stellar population synthesis at the resolution of 2003. Mon. Not. R. Astron. Soc. 344, 1000–1028 (2003).

    ADS  Article  Google Scholar 

  44. 44.

    Papadopoulos, P. P., Thi, W.-F. & Viti, S. C i lines as tracers of molecular gas, and their prospects at high redshifts. Mon. Not. R. Astron. Soc. 351, 147–160 (2004).

    ADS  Article  CAS  Google Scholar 

  45. 45.

    Weiß, A. et al. Gas and dust in the Cloverleaf quasar at redshift 2.5. Astron. Astrophys. 409, L41–L45 (2003).

    ADS  Article  Google Scholar 

  46. 46.

    Weiß, A. et al. Atomic carbon at redshift ~2.5. Astron. Astrophys. 429, L25–L28 (2005).

    ADS  Article  CAS  Google Scholar 

  47. 47.

    Danielson, A. L. R. et al. The properties of the interstellar medium within a star-forming galaxy at z = 2.3. Mon. Not. R. Astron. Soc. 410, 1687–1702 (2011).

    ADS  CAS  Google Scholar 

  48. 48.

    Bothwell, M. S. et al. ALMA observations of atomic carbon in z ~ 4 dusty star-forming galaxies. Mon. Not. R. Astron. Soc. 466, 2825–2841 (2017).

    ADS  Article  Google Scholar 

  49. 49.

    White, G. J. et al. CO and C i maps of the starburst galaxy M 82. Astron. Astrophys. 284, L23–L26 (1994).

    ADS  CAS  Google Scholar 

  50. 50.

    Wilson, C. et al. Luminous infrared galaxies with the submillimeter array. I. Survey overview and the central gas to dust ratio. Astrophys. J. Suppl. Ser. 178, 189–224 (2008).

    ADS  Article  CAS  Google Scholar 

  51. 51.

    Bolatto, A. D., Wolfire, M. & Leroy, A. K. The CO-to-H2 conversion factor. Annu. Rev. Astron. Astrophys. 51, 207–268 (2013).

    ADS  Article  CAS  Google Scholar 

  52. 52.

    Downes, D. & Solomon, P. M. Rotating nuclear rings and extreme starbursts in ultraluminous galaxies. Astrophys. J. 507, 615–654 (1998).

    ADS  Article  CAS  Google Scholar 

  53. 53.

    Carilli, C. L. & Walter, F. Cool gas in high-redshift galaxies. Annu. Rev. Astron. Astrophys. 51, 105–161 (2013).

    ADS  Article  CAS  Google Scholar 

  54. 54.

    Bournaud, F. et al. Modeling CO emission from hydrodynamic simulations of nearby spirals, starbursting mergers, and high-redshift galaxies. Astron. Astrophys. 575, A56 (2015).

    Article  CAS  Google Scholar 

  55. 55.

    Bouche, N. et al. GalPak3D: a Bayesian parametric tool for extracting morphokinematics of galaxies from 3D data. Astrophys. J. 150, 92 (2015).

    Google Scholar 

  56. 56.

    Toomre, A. On the gravitational stability of a disk of stars. Astrophys. J. 139, 1217–1238 (1964).

    ADS  Article  Google Scholar 

  57. 57.

    Wang, B. et al. Gravitational instability and disk star formation. Astrophys. J. 427, 759–769 (1994).

    ADS  Article  Google Scholar 

  58. 58.

    Binney, J. & Tremaine, S. Galactic Dynamics 2nd edn, 494–496 (Princeton Univ. Press, Princeton, 2008).

    MATH  Google Scholar 

  59. 59.

    Romeo, A. B. & Wiegert, J. The effective stability parameter for two-component galactic discs: is \({Q}^{-1}\approx {Q}_{{\rm{stars}}}^{-1}+{Q}_{{\rm{gas}}}^{-1}\)? Mon. Not. R. Astron. Soc. 416, 1191–1196 (2011).

    ADS  Article  Google Scholar 

Download references


We thank J. Baba for discussions about a gravitational instability in SMGs. This work was supported by JSPS KAKENHI JP17J04449. We thank the ALMA staff and in particular the EA-ARC staff for their support. This research has made use of data from ALMA and HerMES project ( ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (South Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. HerMES is a Herschel Key Programme utilizing Guaranteed Time from the SPIRE instrument team, ESAC scientists and a mission scientist. Data analysis was in part carried out on the common-use data analysis computer system at the Astronomy Data Center (ADC) of the National Astronomical Observatory of Japan.

Reviewer information

Nature thanks F. Bournaud and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Author information




K.T. led the project and reduced the ALMA data. K.T. and D.I. wrote the manuscript. M.S.Y. reduced the Large Millimeter Telescope data and edited the final manuscript. Other authors contributed to the interpretation and commented on the ALMA proposal and the paper.

Corresponding author

Correspondence to K. Tadaki.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Galaxy-integrated CO (4–3), CO (1–0) and C i (2–1) spectra of AzTEC-1.

The CO (4–3) spectrum is extracted using an 0.8″-diameter aperture in the natural-weighted map cube. The C i (1–0) and C i (2–1) spectra are extracted from the peak positions in map cubes with 1.7″ × 1.1″ and 0.8″ × 0.7″ resolution, respectively. Yellow shaded regions show the velocity range v = −315 km s−1 to v = +315 km s−1, in which the velocity-integrated line fluxes are measured.

Extended Data Fig. 2 Galaxy-integrated SED of AzTEC-1.

Red circles show the photometric data from Subaru (r′, i′, z′)37, VISTA (Ks)37, Spitzer (3.6 μm, 4.4 μm)37, Herschel (250 μm, 350 μm, 500 μm)38,39, ALMA (860 μm, 2.1 mm, 3.2 mm) and JVLA (10 cm)40. The black line shows the best-fitting SED model from MAGPHYS41,42.

Extended Data Fig. 3 CO spectra along the kinematic major axis.

Spectra are extracted at a position angle of PA = −64°. The spatial offset x from the galactic centre is shown at the upper left of each panel. Red lines indicate the spectra of the best-fitting dynamical model produced by GalPaK3D.

Extended Data Fig. 4 Full MCMC chain for 20,000 iterations.

Red solid lines and black dashed lines indicate the median and 95% confidence interval of the last 60% of the MCMC chain.

Extended Data Table 1 Line fluxes in AzTEC-1

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Tadaki, K., Iono, D., Yun, M.S. et al. The gravitationally unstable gas disk of a starburst galaxy 12 billion years ago. Nature 560, 613–616 (2018).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing