Abstract
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 zā=ā4.3, 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.
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Acknowledgements
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 (http://hermes.sussex.ac.uk/). 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.
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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.
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Extended data figures and tables
Extended Data Fig. 1 Galaxy-integrated CO (4ā3), CO (1ā0) and C i (2ā1) spectra of AzTEC-1.
The CO (4ā3) spectrum is extracted using an 0.8ā³-diameter aperture in the natural-weighted map cube. The CĀ i (1ā0) and CĀ i (2ā1) spectra are extracted from the peak positions in map cubes with 1.7ā³āĆā1.1ā³ and 0.8ā³āĆā0.7ā³ resolution, respectively. Yellow shaded regions show the velocity range vā=āā315Ā kmĀ sā1 to vā=ā+315Ā kmĀ sā1, in which the velocity-integrated line fluxes are measured.
Extended Data Fig. 3 CO spectra along the kinematic major axis.
Spectra are extracted at a position angle of PAā=āā64Ā°. 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.
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Tadaki, K., Iono, D., Yun, M.S. et al. The gravitationally unstable gas disk of a starburst galaxy 12 billion years ago. Nature 560, 613ā616 (2018). https://doi.org/10.1038/s41586-018-0443-1
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DOI: https://doi.org/10.1038/s41586-018-0443-1
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Xinhang Shen
As Einstein's relativity and the Big Bang theory have been disproved, the discovery of this paper gives us a completely new idea about the age of the universe. For 12 billion years, the light of the galaxy has just reached the earth. If the universe then were at the age of 1.8 billion years and it kept expanding in a fixed acceleration from its birth to now, the distance between the earth and the galaxy should be ignorable at that time. The fact that the light has caught the earth now means that the current speed of the earth leaving the location of the galaxy at 12 billion years ago is still smaller than the speed of light. Then the speed of the earth 12 billion years ago leaving the location of the galaxy at 12 billion years ago should be much much smaller than the speed of light. Thus, how could the light needed 12 billion years to catch such a slow moving earth in an ignorable distance? It is obvious a contradiction which tells us that the distance between the earth and the galaxy at 12 billion years ago was not ignorable, but close to 12 billion light years, as the move of the earth during the 12 billion year period is ignorable compared with the distance the light has traveled. As the universe already had such a large size at that moment, the age of the universe then should not be 1.8 billion years old, but much older.
Therefore, the age of the universe now should be much older than 13.8 billion years.
urho rauhala Replied to Xinhang Shen
Good question showing a major flaw of GR based time concept, also shared by some basic mistakes of traditional QM foundations such as Planck energy constant that actually includes the variable speed C4 of the decelerating expansion of Riemann 4-radius R4. The speed of light C along the 3-D space direction orthogonal to R4 direction is closely coupled to the dynamic contraction/expansion speed C4 such that the balance of the motion and gravitational energies of total mass M in universe is continually preserved. The ticking rate of atomic clocks and other processes (such as decay rate) at small values of R4 such as 1.8B l.y was close to 1,000 times higher than today such that in terms of today's definition of 'prolonged' second the GR based age 13.8 B yrs reduces to 9.2B yrs. This explains the fast star formation process of the ALMA observed disk while also revealing some 5-10 other blunders of GR/QM based postulates, including the 'epicycle mistakes' of Dark Energy/Matter, GW etc. See the books and papers of 'Suntola Dynamic Universe' bounce (vs BB) theory since 1995, collected today at PFS web site for open view.
Also note the 'cosmic entanglement' principle of DU where the motion of any mass object, such as Earth from its birth to today, has been continually interconnected (in a 'pipeline' fashion) to the gravitational states of ALL other mass objects of universe, acting as its 'anti-matter counterpart'. The same principle applies to binary star/NS/BH pairs during millions/billions of years before their local merge event - no or little unbalanced energy left to cause the GR postulated emission of GW for detection at the global optical or 'gravitational' distance of over 100 M years. See DU explanation of the 'indirect GR proof of GW' granted Nobel award in 1990's and paving the funding of LIGO related developments, unaware of the more general digital software/hardware developments of array algebra in digital photogrammetry and geodesy since 1975. The learned lessons of both DE/DM, GW and related automated multi-ray stereo image matching and range sensing/ultra-accurate time keeping technologies of array calculus are valuable for the new technologies of cosmic mapping projects. WFIRST and Gaia/Hubble efforts are partially wasted as they were inspired by the 2011 and 2017 Nobel 'confirmations' of GR based DE and GW mistakes.