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The Sagittarius impact as an architect of spirality and outer rings in the Milky Way

Nature volume 477, pages 301–303 (2011)Cite this article

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Abstract

Like many galaxies of its size, the Milky Way is a disk with prominent spiral arms rooted in a central bar1, although our knowledge of its structure and origin is incomplete. Traditional attempts to understand our Galaxy’s morphology assume that it has been unperturbed by major external forces. Here we report simulations of the response of the Milky Way to the infall of the Sagittarius2 dwarf galaxy (Sgr), which results in the formation of spiral arms, influences the central bar and produces a flared outer disk. Two ring-like wrappings emerge towards the Galactic anti-Centre in our model that are reminiscent of the low-latitude arcs observed in the same area of the Milky Way. Previous models have focused on Sgr itself3,4 to reproduce the dwarf’s orbital history and place associated constraints on the shape of the Milky Way gravitational potential, treating the Sgr impact event as a trivial influence on the Galactic disk. Our results show that the Milky Way’s morphology is not purely secular in origin and that low-mass minor mergers predicted to be common throughout the Universe5 probably have a similarly important role in shaping galactic structure.

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Figure 1: Visualizations of evolved disk end states in the simulation suite.
Figure 2: Face-on surface density visualizations of the Milky Way at four important moments during the ‘light Sgr’ simulation.
Figure 3: The observed Sgr tidal debris stream and remnant core in comparison to our ‘light Sgr’ simulation, in equatorial coordinates.
Figure 4: Endstate disk overdensities in the ‘heavy Sgr’ simulation.

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References

  1. Pohl, M., Englmaier, P. & Bissantz, N. Three-dimensional distribution of molecular gas in the barred Milky Way. Astrophys. J. 677, 283–291 (2008)

    Article  ADS  CAS  Google Scholar 

  2. Ibata, R. A., Gilmore, G. & Irwin, M. J. A dwarf satellite galaxy in Sagittarius. Nature 370, 194–196 (1994)

    Article  ADS  Google Scholar 

  3. Law, D. R., Johnston, K. V. & Majewski, S. R. A Two Micron All-Sky Survey view of the Sagittarius dwarf galaxy. IV. Modeling the Sagittarius tidal tails. Astrophys. J. 619, 807–823 (2005)

    Article  ADS  Google Scholar 

  4. Law, D. R. & Majewski, S. R. The Sagittarius dwarf galaxy: a model for evolution in a triaxial Milky Way halo. Astrophys. J. 714, 229–254 (2010)

    Article  ADS  Google Scholar 

  5. Johnston, K. V., Spergel, D. N. & Hernquist, L. The disruption of the Sagittarius dwarf galaxy. Astrophys. J. 451, 598–606 (1995)

    Article  ADS  Google Scholar 

  6. Niederste-Ostholt, M., Belokurov, V., Evans, N. W. & Peñarrubia, J. Re-assembling the Sagittarius dwarf galaxy. Astrophys. J. 712, 516–526 (2010)

    Article  ADS  Google Scholar 

  7. Conroy, C. & Wechsler, R. H. Connecting galaxies, halos, and star formation rates across cosmic time. Astrophys. J. 696, 620–635 (2009)

    Article  ADS  Google Scholar 

  8. Behroozi, P. S., Conroy, C. & Wechsler, R. H. A comprehensive analysis of uncertainties affecting the stellar mass-halo mass relation for 0 < z < 4. Astrophys. J. 717, 379–403 (2010)

    Article  ADS  CAS  Google Scholar 

  9. Widrow, L. M., Pym, B. & Dubinski, J. Dynamical blueprints for galaxies. Astrophys. J. 679, 1239–1259 (2008)

    Article  ADS  Google Scholar 

  10. Bissantz, N. & Gerhard, O. Spiral arms, bar shape and bulge microlensing in the Milky Way. Mon. Not. R. Astron. Soc. 330, 591–608 (2002)

    Article  ADS  Google Scholar 

  11. Nordström, B. et al. The Geneva-Copenhagen survey of the solar neighbourhood. Ages, metallicities, and kinematic properties of ∼14,000 F and G dwarfs. Astron. Astrophys. 418, 989–1029 (2004)

    Article  ADS  Google Scholar 

  12. Dinescu, D. I., Girard, T. M., van Altena, W. F. & López, C. E. Absolute Proper Motion of the Sagittarius Dwarf Galaxy and of the Outer Regions of the Milky Way Bulge. Astrophys. J. 618, L25–L28 (2005)

    Article  ADS  Google Scholar 

  13. Majewski, S. R., Skrutskie, M. F., Weinberg, M. D. & Ostheimer, J. C. A Two Micron All Sky Survey view of the Sagittarius dwarf galaxy. I. Morphology of the Sagittarius core and tidal arms. Astrophys. J. 599, 1082–1115 (2003)

    Article  ADS  Google Scholar 

  14. Kunder, A. & Chaboyer, B. Distance to the Sagittarius dwarf galaxy using Macho Project RR Lyrae stars. Astron. J. 137, 4478–4486 (2009)

    Article  ADS  Google Scholar 

  15. Lokas, E. L. et al. The inner structure and kinematics of the Sagittarius dwarf galaxy as a product of tidal stirring. Astrophys. J. 725, 1516–1527 (2010)

    Article  ADS  Google Scholar 

  16. Peñarrubia, J. et al. A comprehensive model for the Monoceros tidal stream. Astrophys. J. 626, 128–144 (2005)

    Article  ADS  Google Scholar 

  17. Momany, Y. et al. Outer structure of the Galactic warp and flare: explaining the Canis Major over-density. Astron. Astrophys. 451, 515–538 (2006)

    Article  ADS  CAS  Google Scholar 

  18. Kazantzidis, S., Bullock, J. S., Zentner, A. R., Kravtsov, A. V. & Moustakas, L. A. Cold Dark Matter substructure and galactic disks. I. Morphological signatures of hierarchical satellite accretion. Astrophys. J. 688, 254–276 (2008)

    Article  ADS  Google Scholar 

  19. Navarro, J. F., Frenk, C. S. & White, S. D. M. The structure of cold dark matter halos. Astrophys. J. 462, 563–575 (1996)

    Article  ADS  CAS  Google Scholar 

  20. Zemp, M., Moore, B., Stadel, J., Carollo, C. M. & Madau, P. Multimass spherical structure models for N-body simulations. Mon. Not. R. Astron. Soc. 386, 1543–1556 (2008)

    Article  ADS  Google Scholar 

  21. King, I. R. The profile of a star image. Publ. Astron. Soc. Pacif. 83, 199–201 (1971)

    Article  ADS  Google Scholar 

  22. Keselman, J. A., Nusser, A. & Peebles, P. J. E. Galaxy satellites and the weak equivalence principle. Phys. Rev. D. 80, 063517 (2009)

    Article  ADS  Google Scholar 

  23. Levine, E. S., Blitz, L. & Heiles, C. The spiral structure of the outer Milky Way in hydrogen. Science 312, 1773–1777 (2006)

    Article  ADS  CAS  Google Scholar 

  24. Reid, M. J. et al. Trigonometric parallaxes of massive star-forming regions. VI. Galactic structure, fundamental parameters, and noncircular motions. Astrophys. J. 700, 137–148 (2009)

    Article  ADS  CAS  Google Scholar 

  25. Sellwood, J. A. The lifetimes of spiral patterns in disc galaxies. Mon. Not. R. Astron. Soc. 410, 1637–1646 (2010)

    ADS  Google Scholar 

  26. Struck, C., Dobbs, C. L. & Hwang, J.-S. Slowly-breaking waves: the longevity of tidally induced spiral structure. Mon. Not. R. Astron. Soc. 414, 2498–2510 (2011)

    Article  ADS  CAS  Google Scholar 

  27. Majewski, S. R. et al. A Two Micron All Sky Survey view of the sagittarius dwarf galaxy. II. Swope telescope spectroscopy of M giant stars in the dynamically cold Sagittarius tidal stream. Astron. J. 128, 245–259 (2004)

    Article  ADS  Google Scholar 

  28. Correnti, M., Bellazzini, M., Ibata, R. A., Ferraro, F. R. & Varghese, A. The northern wraps of the Sagittarius stream as traced by red clump stars: distances, intrinsic widths, and stellar densities. Astrophys. J. 721, 329–356 (2010)

    Article  ADS  Google Scholar 

  29. Grillmair, C. J. Substructure in tidal streams: tributaries in the anticenter stream. Astrophys. J. 651, L29–L32 (2006)

    Article  ADS  Google Scholar 

  30. Ibata, R. A., Irwin, M. J., Lewis, G. F., Ferguson, A. M. N. & Tanvir, N. One ring to encompass them all: a giant stellar structure that surrounds the Galaxy. Mon. Not. R. Astron. Soc. 340, L21–L27 (2003)

    Article  ADS  Google Scholar 

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Acknowledgements

We would like to thank K. Johnston, M. Kaplinghat, D. Law, H. Morrison and A. Zentner for discussions and C. Struck for suggestions that improved this work. All simulations were performed on the GreenPlanet cluster at the University of California, Irvine.

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Authors and Affiliations

  1. Department of Physics and Astronomy, The University of Pittsburgh, Pittsburgh, 15260, Pennsylvania, USA

    Chris W. Purcell

  2. Department of Physics and Astronomy, Center for Cosmology, The University of California, Irvine, 92697, California, USA

    Chris W. Purcell, James S. Bullock, Erik J. Tollerud & Miguel Rocha

  3. Department of Physics, Florida Atlantic University, Boca Raton, 33431, Florida, USA

    Sukanya Chakrabarti

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  1. Chris W. Purcell
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  2. James S. Bullock
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  3. Erik J. Tollerud
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  4. Miguel Rocha
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  5. Sukanya Chakrabarti
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Contributions

C.W.P. helped to conceive the project, performed and analysed all simulations, and wrote the majority of the text. J.S.B. helped to conceive the project, contributed to the analysis, and co-authored the text. E.J.T. created the 3D visualizations and provided discussion and direction related to observational correlations. M.R. provided the code that was utilized to initialize the Sagittarius progenitors and insight on how to thereby achieve the desired properties of these systems. S.C. assisted with interpretation and analysis of the stellar disk instabilities and their time evolution.

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Correspondence to Chris W. Purcell.

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The authors declare no competing financial interests.

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Purcell, C., Bullock, J., Tollerud, E. et al. The Sagittarius impact as an architect of spirality and outer rings in the Milky Way. Nature 477, 301–303 (2011). https://doi.org/10.1038/nature10417

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