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A dynamically young and perturbed Milky Way disk - Nature

  • ️Soubiran, C.
  • ️Wed Sep 19 2018

Data availability

The datasets used and analysed for this study are derived from data available in the public Gaia archive (https://gea.esac.esa.int/archive). The Bayesian distances for the Gaia sources with radial velocity37are available at http://www.astro.lu.se/~paul/GaiaDR2_RV_star_distance.csv.gz. The rest of the relevant datasets and toy models are available from the corresponding author on reasonable request.

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Acknowledgements

This work made use of data from ESA mission Gaia (https://www.cosmos.esa.int/gaia), which was processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This project received funding from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement number 745617. This work was supported by the MDM-2014-0369 of ICCUB (Unidad de Excelencia ‘María de Maeztu’) and the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement GENIUS FP7-606740. A.H. acknowledges financial support from a VICI grant from the Netherlands Organisation for Scientific Research (NWO). We acknowledge the MINECO (Spanish Ministry of Economy) through grants ESP2016-80079-C2-1-R (MINECO/FEDER, UE) and ESP2014-55996-C2-1-R (MINECO/FEDER, UE). This work been funded in part by the Agenzia Spaziale Italiana (ASI) through contract 2014-025-R.1.2015 through the Italian Istituto Nazionale di Astrofisica (INAF). E.P. acknowledges the financial support of the 2014 PhD fellowship programme of INAF.

Author information

Authors and Affiliations

  1. Institut de Ciències del Cosmos, Universitat de Barcelona (IEEC-UB), Barcelona, Spain

    T. Antoja, M. Romero-Gómez & F. Figueras

  2. Kapteyn Astronomical Institute, University of Groningen, Groningen, The Netherlands

    A. Helmi

  3. GEPI, Observatoire de Paris, Université PSL, CNRS, Meudon, France

    D. Katz & C. Babusiaux

  4. Université Grenoble Alpes, CNRS, IPAG, Grenoble, France

    C. Babusiaux

  5. INAF—Osservatorio Astrofisico di Torino, Pino Torinese, Italy

    R. Drimmel & E. Poggio

  6. Institute of Astronomy, University of Cambridge, Cambridge, UK

    D. W. Evans

  7. Università di Torino, Dipartimento di Fisica, Torino, Italy

    E. Poggio

  8. Institut UTINAM, CNRS UMR6213, Université Bourgogne Franche-Comté, OSU THETA Franche-Comté Bourgogne, Observatoire de Besançon, Besançon, France

    C. Reylé & A. C. Robin

  9. Mullard Space Science Laboratory, University College London, Dorking, UK

    G. Seabroke

  10. Laboratoire d’astrophysique de Bordeaux, Université Bordeaux, CNRS, Pessac, France

    C. Soubiran

Authors

  1. T. Antoja

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  2. A. Helmi

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  3. M. Romero-Gómez

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  4. D. Katz

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  5. C. Babusiaux

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  6. R. Drimmel

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  7. D. W. Evans

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  8. F. Figueras

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  9. E. Poggio

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  10. C. Reylé

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  11. A. C. Robin

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  12. G. Seabroke

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  13. C. Soubiran

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Contributions

T.A. contributed to the sample preparation, analysed and interpreted the data, performed most of the modelling and wrote the paper together with A.H. A.H. also provided interpretation of the findings. M.R.-G. performed the simulation with the barred potential and contributed to sample preparation. D.K., C.B., R.D., D.W.E., F.F., E.P., C.R., A.C.R., G.S. and C.S. contributed to sample preparation and validation of the Gaia data. All authors reviewed the manuscript.

Corresponding author

Correspondence to T. Antoja.

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Extended data figures and tables

Extended Data Fig. 1 Velocities of the stars at the solar Galactocentric radius.

Two-dimensional histograms of combinations of radial, azimuthal and vertical Galactic cylindrical velocities for the stars in our sample of Gaia data located at 8.24 kpc < R < 8.44 kpc, in bins of 1 km s−1. VR and Vϕ are positive towards the Galactic anticentre and the direction of Galactic rotation, respectively. The darkness is proportional to the number of counts. a, Although the bimodality seen here, separating the Hercules stream from the rest of the distribution, was known45,46, as well as some other elongated structures in this velocity projection11,47,48, the numerous and thin arches are a new phenomenon revealed by Gaia data12. The semi-circular dotted line marks an arbitrary line of constant kinetic energy in the plane \({E}_{k}=({V}_{R}^{2}+{V}_{\phi }^{2})/2\), as predicted for the substructure generated in horizontal phase mixing7,8. b, The data have a box-like appearance, where the extent in VZ of the arches varies with Vϕ (arrows), probably created by the correlation between the spiral shape and Vϕ seen in Fig. 1c. c, Although some velocity asymmetries where noticed before in the Vϕ–VZ projection11 and attributed to the Galaxy warp, the sharp shell-like features involving VZ, especially at VZ ≈ −30 km s−1 and VZ ≈ 25 km s−1, were not previously evident. These shells are different projections of the snail shell pattern of Fig. 1a.

Extended Data Fig. 2 Location of the stars in the sample.

a, b, Two-dimensional histograms with bins of 0.05 kpc in the X–Y (a) and X–Z (b) projections of our sample of Gaia data. The dotted lines mark the selection of stars in the solar Galactic ring between radii of 8.24 kpc and 8.44 kpc. The Sun is located at (X, Y, Z) = (−8.34, 0, 0.027) kpc and the Galactic centre (GC) is marked with a black dot.

Extended Data Fig. 3 Modelled vertical positions and velocities of stars with time.

The plots show the snail shells created in the phase space evolution under an anharmonic potential. a–c, Phase-space evolution at different times (t = 0, 10, 100, 200, 1,000 Myr) for an ensemble of particles at a fixed Galactocentric radius of R = 8.5 kpc with an initial Gaussian distribution in Z(t = 0) with mean of −0.1 kpc and dispersion of 0.04 kpc and in VZ(t = 0) with mean of −2 km s−1 and dispersion of 1 km s−1. d–f, Same as a–c, but for a skewed normal distribution of initial radius with skewness of 10, location parameter of 8.4 kpc and scale parameter of 0.2 kpc. In all cases, the evolution is under an anharmonic oscillator derived from the expansion of a Miyamoto–Nagai disk for small Z. In a and d the stars are colour-coded by vertical period.

Extended Data Fig. 4 Vertical frequency for orbits in a Galaxy model.

a, b, Frequencies as a function of Galactocentric radius R computed in the updated model from ref. 41, colour coded by the vertical amplitude (a) and by the vertical velocity amplitude (b) of the orbits.

Extended Data Fig. 5 Position of the spiral turns in the vertical positions and velocities.

The Z–VZ plane for stars at Galactocentric radii of 8.24 kpc to 8.44 kpc, coloured as a function of median guiding radius Rg in bins of ΔZ = 0.04 kpc and ΔVZ = 2 km s−1, with vertical and horizontal lines showing the approximate locations of the observed snail shell (turn-around and mid-plane points).

Extended Data Table 1 Time estimates from the turn-around points of the spiral

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Extended Data Table 2 Time estimates from the mid-plane points of the spiral

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Antoja, T., Helmi, A., Romero-Gómez, M. et al. A dynamically young and perturbed Milky Way disk. Nature 561, 360–362 (2018). https://doi.org/10.1038/s41586-018-0510-7

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  • Received: 26 April 2018

  • Accepted: 26 July 2018

  • Published: 19 September 2018

  • Issue Date: 20 September 2018

  • DOI: https://doi.org/10.1038/s41586-018-0510-7

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