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Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk

Nature volume 555, pages 334–337 (2018)Cite this article

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Abstract

Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter1,2. The stellar halo—the faint, roughly spherical component of the Galaxy—reveals rich ‘fossil’ evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components3,4,5. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins6,7. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk8,9,10. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane—locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies11,12.

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Figure 1: Locations of the observed stars in Galactocentric Cartesian coordinates.
Figure 2: Chemical abundances of the observed stars.
Figure 3: Comparison of the positions of the observed stars with an N-body simulation.

References

  1. Freeman, K. & Bland-Hawthorn, J. The new galaxy: signatures of its formation. Annu. Rev. Astron. Astrophys. 40, 487–537 (2002)

    Article  ADS  Google Scholar 

  2. Bullock, J. S. & Johnston, K. V. Tracing galaxy formation with stellar halos. I. Methods. Astrophys. J. 635, 931–949 (2005)

    Article  ADS  Google Scholar 

  3. Helmi, A., White, S. D. M., de Zeeuw, P. T. & Zhao, H. Debris streams in the solar neighbourhood as relicts from the formation of the Milky Way. Nature 402, 53–55 (1999)

    Article  ADS  CAS  Google Scholar 

  4. Bell, E. F. et al. The accretion origin of the Milky Way’s stellar halo. Astrophys. J. 680, 295–311 (2008)

    Article  ADS  CAS  Google Scholar 

  5. Nissen, P. E. & Schuster, W. J. Two distinct halo populations in the solar neighborhood. Evidence from stellar abundance ratios and kinematics. Astron. Astrophys. 511, L10 (2010)

    Article  ADS  CAS  Google Scholar 

  6. Helmi, A. et al. Pieces of the puzzle: ancient substructure in the Galactic disc. Mon. Not. R. Astron. Soc. 365, 1309–1323 (2006)

    Article  ADS  CAS  Google Scholar 

  7. Stonkute, E., Tautvaišiene˙, G., Nordström, B. & Ženoviene˙, R. Stellar substructures in the solar neighbourhood. I. Kinematic group 3 in the Geneva-Copenhagen survey. Astron. Astrophys. 541, A157 (2012)

    Article  ADS  CAS  Google Scholar 

  8. Xu, Y. et al. Rings and radial waves in the disk of the Milky Way. Astrophys. J. 801, 105 (2015)

    Article  ADS  CAS  Google Scholar 

  9. Purcell, C. W., Bullock, J. S., Tollerud, E. J., Rocha, M. & Chakrabarti, S. The Sagittarius impact as an architect of spirality and outer rings in the Milky Way. Nature 477, 301–303 (2011)

    Article  ADS  CAS  PubMed  Google Scholar 

  10. Dorman, C. E. et al. A new approach to detailed structural decomposition from the SPLASH and PHAT surveys: kicked-up disk stars in the Andromeda galaxy? Astrophys. J. 779, 103 (2013)

    Article  ADS  Google Scholar 

  11. 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 

  12. Price-Whelan, A. M., Johnston, K. V., Sheffield, A. A., Laporte, C. F. P. & Sesar, B. A reinterpretation of the Triangulum-Andromeda stellar clouds: a population of halo stars kicked out of the Galactic disc. Mon. Not. R. Astron. Soc. 452, 676–685 (2015)

    Article  ADS  CAS  Google Scholar 

  13. Rocha-Pinto, H. J., Majewski, S. R., Skrutskie, M. F., Crane, J. D. & Patterson, R. J. Exploring halo substructure with giant stars: a diffuse star cloud or tidal debris around the Milky Way in Triangulum-Andromeda. Astrophys. J. 615, 732–737 (2004)

    Article  ADS  CAS  Google Scholar 

  14. Martin, N. F., Ibata, R. A. & Irwin, M. Galactic halo stellar structures in the Triangulum-Andromeda region. Astrophys. J. 668, L123–L126 (2007)

    Article  ADS  CAS  Google Scholar 

  15. Sheffield, A. A. et al. Exploring halo substructure with giant stars. XIV. The nature of the Triangulum-Andromeda stellar features. Astrophys. J. 793, 62 (2014)

    Article  ADS  Google Scholar 

  16. Sharma, S. et al. Group finding in the stellar halo using M-giants in the Two Micron All Sky Survey: an extended view of the Pisces overdensity? Astrophys. J. 722, 750–759 (2010)

    Article  ADS  Google Scholar 

  17. Li, T. S. et al. Exploring halo substructure with giant stars. XV. Discovery of a connection between the Monoceros Ring and the Triangulum-Andromeda overdensity? Astrophys. J. 844, 74 (2017)

    Article  ADS  CAS  Google Scholar 

  18. Johnston, K. V. et al. Disk heating, galactoseismology, and the formation of stellar halos. Galaxies 5, 3 (2017)

    Article  Google Scholar 

  19. Xue, X. X. et al. The Milky Way’s circular velocity curve to 60 kpc and an estimate of the dark matter halo mass from the kinematics of 2400 SDSS blue horizontal-branch stars. Astrophys. J. 684, 1143–1158 (2008)

    Article  ADS  CAS  Google Scholar 

  20. Bensby, T., Feltzing, S., Oey, M. S. Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood. Astron. Astrophys. 562, A71 (2014)

    Article  ADS  CAS  Google Scholar 

  21. Magrini, L. et al. The Gaia-ESO survey: radial distribution of abundances in the Galactic disc from open clusters and young-field stars. Astron. Astrophys. 603, A2 (2017)

    Article  CAS  Google Scholar 

  22. Yong, D., Carney, B.W., Friel, E.D. Elemental abundance ratios in stars of the outer galactic disk. IV. A new sample of open clusters. Astron. J. 144, 95 (2012)

    Article  ADS  CAS  Google Scholar 

  23. Feast, M. W., Menzies, J. W., Matsunaga, N. & Whitelock, P. A. Cepheid variables in the flared outer disc of our galaxy. Nature 509, 342–344 (2014)

    Article  ADS  CAS  PubMed  Google Scholar 

  24. Kovtyukh, V. et al. The chemical composition of Galactic beat Cepheids. Mon. Not. R. Astron. Soc. 460, 2077–2086 (2016)

    Article  ADS  CAS  Google Scholar 

  25. Odenkirchen, M., Grebel, E. K., Dehnen, W., Rix, H.-W. & Cudworth, K. M. Kinematic study of the disrupting globular cluster Palomar 5 using VLT spectra. Astron. J. 124, 1497–1510 (2002)

    Article  ADS  CAS  Google Scholar 

  26. Gratton, R., Sneden, C. & Carretta, E. Abundance variations within globular clusters. Annu. Rev. Astron. Astrophys. 42, 385–440 (2004)

    Article  ADS  CAS  Google Scholar 

  27. Tolstoy, E., Hill, V. & Tosi, M. Star-formation histories, abundances, and kinematics of dwarf galaxies in the Local Group. Annu. Rev. Astron. Astrophys. 47, 371–425 (2009)

    Article  ADS  CAS  Google Scholar 

  28. Gómez, F. A. et al. Vertical density waves in the Milky Way disc induced by the Sagittarius dwarf galaxy. Mon. Not. R. Astron. Soc. 429, 159–164 (2013)

    Article  ADS  Google Scholar 

  29. Laporte, C. F. P., Johnston, K. V., Gómez, F. A., Garavito-Camargo, N. & Besla, G. The influence of Sagittarius and the Large Magellanic Cloud on the Milky Way galaxy. Preprint at https://arxiv.org/abs/1710.02538 (2017)

  30. Vogt, S. S. et al. HIRES: the high-resolution echelle spectrometer on the Keck 10-m telescope. Proc. SPIE Int. Soc. Opt. Eng. 2198, 362 (1994)

    ADS  CAS  Google Scholar 

  31. Freudling, W. et al. Automated data reduction workflows for astronomy. The ESO reflex environment. Astron. Astrophys. 559, A96 (2013)

    Article  Google Scholar 

  32. Gustafsson, B. et al. A grid of MARCS model atmospheres for late-type stars. I. Methods and general properties. Astron. Astrophys. 486, 951–970 (2008)

    Article  ADS  CAS  Google Scholar 

  33. Weck, P. F., Schweitzer, A., Stancil, P. C., Hauschildt, P. H. & Kirby, K. The molecular continuum opacity of 24MgH in cool stellar atmospheres. Astrophys. J. 584, 459–464 (2003)

    Article  ADS  CAS  Google Scholar 

  34. Ruchti, G. R., Bergemann, M., Serenelli, A., Casagrande, L. & Lind, K. Unveiling systematic biases in the 1D LTE excitation-ionization balance of Fe for FGK stars: a novel approach to determination of stellar parameters. Mon. Not. R. Astron. Soc. 429, 126–134 (2013)

    Article  ADS  CAS  Google Scholar 

  35. Casagrande, L., Ramirez, I., Melendez, J., Bessell, M., Asplund, M. An absolutely calibrated Teff scale from the infrared flux method. Dwarfs and subgiants. Astron. Astrophys. 512, A54 (2010)

    Article  ADS  CAS  Google Scholar 

  36. Casagrande, L. et al. Towards stellar effective temperatures and diameters at 1 per cent accuracy for future surveys. Mon. Not. R. Astron. Soc. 439, 2060–2073 (2014)

    Article  ADS  Google Scholar 

  37. Kunder, A. et al. The radial velocity experiment (RAVE): fifth data release. Astron. J. 153, 75 (2017)

    Article  ADS  CAS  Google Scholar 

  38. Lind, K., Bergemann, M. & Asplund, M. Non-LTE line formation of Fe in late-type stars—II. 1D spectroscopic stellar parameters. Mon. Not. R. Astron. Soc. 427, 50–60 (2012)

    Article  ADS  CAS  Google Scholar 

  39. Valenti, J. A. & Piskunov, N. E. Spectroscopy made easy. A new tool for fitting observations with synthetic spectra. Astron. Astrophys. Suppl. Ser. 118, 595–603 (1996)

    Article  ADS  Google Scholar 

  40. Bergemann, M., Collet, R., Amarsi, A.M., Kovalev, M., Ruchti, G., Magic, Z. Non-local thermodynamic equilibrium stellar spectroscopy with 1D and <3D> models. I. Methods and application to magnesium abundances in standard stars. Astrophys. J. 847, 15 (2017)

    Article  ADS  CAS  Google Scholar 

  41. Bergemann, M., Lind, K., Collet, R., Magic, Z. & Asplund, M. Non-LTE line formation of Fe in late-type stars—I. Standard stars with 1D and <3D> model atmospheres. Mon. Not. R. Astron. Soc. 427, 27–49 (2012)

    Article  ADS  CAS  Google Scholar 

  42. Storey, P. J. & Zeippen, C. J. Theoretical values for the [Oiii] 5007/4959 line-intensity ratio and homologous cases. Mon. Not. R. Astron. Soc. 312, 813–816 (2000)

    Article  ADS  CAS  Google Scholar 

  43. Smette, A. et al. Molecfit: a general tool for telluric absorption correction. I. Method and application to ESO instruments. Astron. Astrophys. 576, A77 (2015)

    Article  CAS  Google Scholar 

  44. Amarsi, A. M., Asplund, M., Collet, R. & Leenaarts, J. Non-LTE oxygen line formation in 3D hydrodynamic model stellar atmospheres. Mon. Not. R. Astron. Soc. 455, 3735–3751 (2016)

    Article  ADS  CAS  Google Scholar 

  45. Lemasle, B. et al. VLT/FLAMES spectroscopy of red giant branch stars in the Fornax dwarf spheroidal galaxy. Astron. Astrophys. 572, A88 (2014)

    Article  CAS  Google Scholar 

  46. Lind, K., Asplund, M., Barklem, P. S., Belyaev, A. K. Non-LTE calculations for neutral Na in late-type stars using improved atomic data. Astron. Astrophys. 528, A103 (2011)

    Article  ADS  CAS  Google Scholar 

  47. Bergemann, M. Ionization balance of Ti in the photospheres of the Sun and four late-type stars. Mon. Not. R. Astron. Soc. 413, 2184–2198 (2011)

    Article  ADS  CAS  Google Scholar 

  48. Korotin, S.A. et al. Grid of theoretical NLTE equivalent widths of four Ba ii lines and barium abundance in cool stars. Astron. Astrophys. 581, A70 (2015)

    Article  CAS  Google Scholar 

  49. Villemoes, P., Arnesen, A., Heijkenskjold, F. & Wannstrom, A. Isotope shifts and hyperfine structure of 134–138Ba ii by fast ion beam-laser spectroscopy. J. Phys. B 26, 4289–4299 (1993)

    Article  ADS  CAS  Google Scholar 

  50. Van Hove, M., Borghs, G., DeBisschop, P. & Silverans, R. E. J-dependent isotope shifts in the 5d2DJ doublet of barium ii. J. Phys. B 15, 1805–1809 (1982)

    Article  ADS  CAS  Google Scholar 

  51. Silverans, R. E., Borghs, G., de Bisschop, P. & van Hove, M. Hyperfine structure of the 5d 2DJ states in the alkaline-earth Ba ion by fast-ion-beam laser-rf spectroscopy. Phys. Rev. A 33, 2117–2120 (1986)

    Article  ADS  CAS  Google Scholar 

  52. Lawler, J. E., Wickliffe, M. E., den Hartog, E. A. & Sneden, C. Improved laboratory transition parameters for Eu ii and application to the solar europium elemental and isotopic composition. Astrophys. J. 563, 1075–1088 (2001)

    Article  ADS  CAS  Google Scholar 

  53. Villemoes, P., Arnesen, A., Heijkenskjold, F., Kastberg, A. & Wannstrom, A. Hyperfine structure measurements of 151,153Eu ii with fast ion beam-laser spectroscopy. Phys. Lett. A 162, 178–181 (1992)

    Article  ADS  CAS  Google Scholar 

  54. Asplund, M., Grevesse, N., Sauval, A. J. & Scott, P. The chemical composition of the Sun. Annu. Rev. Astron. Astrophys. 47, 481–522 (2009)

    Article  ADS  CAS  Google Scholar 

  55. Serenelli, A. M., Bergemann, M., Ruchti, G. & Casagrande, L. Bayesian analysis of ages, masses and distances to cool stars with non-LTE spectroscopic parameters. Mon. Not. R. Astron. Soc. 429, 3645–3657 (2013)

    Article  ADS  CAS  Google Scholar 

  56. Bovy, J. et al. The stellar population structure of the Galactic disk. Astrophys. J. 823, 30 (2016)

    Article  ADS  Google Scholar 

  57. Schönrich, R. Galactic rotation and solar motion from stellar kinematics. Mon. Not. R. Astron. Soc. 427, 274–287 (2012)

    Article  ADS  Google Scholar 

  58. McWilliam, A. & Smecker-Hane, T. A. in Cosmic Abundances as Records of Stellar Evolution and Nucleosynthesis (eds Randich, S. & Pasquini, L. ) 236–237 (Springer, 2005)

  59. Sbordone, L. et al. The exotic chemical composition of the Sagittarius dwarf spheroidal galaxy. Astron. Astrophys. 465, 815–824 (2007)

    Article  ADS  CAS  Google Scholar 

  60. Mucciarelli, A. et al. Chemical abundances in the nucleus of the Sagittarius dwarf spheroidal galaxy. Astron. Astrophys. 605, A46 (2017)

    Article  CAS  Google Scholar 

  61. Shetrone, M. et al. VLT/UVES abundances in four nearby dwarf spheroidal galaxies. I. Nucleosynthesis and abundance ratios. Astron. J. 125, 684–706 (2003)

    Article  ADS  CAS  Google Scholar 

  62. Kirby, E. N. et al. Multi-element abundance measurements from medium-resolution spectra. II. Catalog of stars in Milky Way dwarf satellite galaxies. Astrophys. J. Suppl. Ser. 191, 352–375 (2010)

    Article  ADS  CAS  Google Scholar 

  63. Letarte, B. et al. A high-resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy. Astron. Astrophys. 523, A17 (2010)

    Article  CAS  Google Scholar 

  64. Cohen, J. G. & Melendez, J. Abundances in a large sample of stars in M3 and M13. Astron. J. 129, 303–329 (2005)

    Article  ADS  CAS  Google Scholar 

  65. Ramírez, S. V. & Cohen, J. G. Abundances in stars from the red giant branch tip to near the main-sequence turnoff in M71. III. Abundance ratios. Astron. J. 123, 3277–3297 (2002)

    Article  ADS  Google Scholar 

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Acknowledgements

We thank I. Georgiev for help with the telluric correction of the stellar spectrum taken with the UVES spectrograph at the VLT. A.M.S. was supported by grants ESP2015-66134-R and ESP2017-82674-R (MINECO). K.V.J.’s contributions were supported by a grant from the National Science Foundation (AST-1614743). L.C. acknowledges support from the Australian Research Council (grants DP150100250 and FT160100402). Parts of this research were conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. M.B. acknowledges support from Collaborative Research Center SFB 881 (Heidelberg University, subproject A5) of the Deutsche Forschungsgemeinschaft. C.F.P.L. is supported by a Junior Fellow of the Simons Society of Fellows award from the Simons Foundation. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number OCI-1053575. R.S. is supported by a Royal Society University Research Fellowship. We thank S. Majewski and K. Cunha for interesting discussions on the topic, and J. Bovy for help with implementing the disk-flare profile. We thank T. Müller for assistance with the final, production-quality versions of all figures. We thank the people who realized the Keck Telescope and its instruments and those who operate and maintain the Keck Observatory. We thank the indigenous Hawaiian community for their generous hospitality on their sacred mountain.

Author information

Authors and Affiliations

  1. Max Planck Institute for Astronomy, Koenigstuhl 17, Heidelberg, 69117, Germany

    Maria Bergemann & Andrew Gould

  2. Deutsche Börse AG, Mergenthalerallee 61, Eschborn, 65760, Germany

    Branimir Sesar

  3. Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, 91125, California, USA

    Judith G. Cohen

  4. Institute of Space Sciences (ICE, CSIC), Carrer de Can Magrans, Barcelona, E-08193, Spain

    Aldo M. Serenelli

  5. Institut d’Estudis Espacials de Catalunya (IEEC), C/Gran Capita, 2-4, Barcelona, E-08034, Spain

    Aldo M. Serenelli

  6. Department of Natural Sciences, LaGuardia Community College, City University of New York, 31-10 Thomson Avenue, Long Island City, 11101, New York, USA

    Allyson Sheffield

  7. Fermi National Accelerator Laboratory, PO Box 500, Batavia, 60510, Illinois, USA

    Ting S. Li

  8. Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, Canberra, 2611, Australian Capital Territory, Australia

    Luca Casagrande

  9. ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia,

    Luca Casagrande

  10. Department of Astronomy, Columbia University, 550 West 120th Street, Mail Code 5246, New York, 10027, New York, USA

    Kathryn V. Johnston & Chervin F. P. Laporte

  11. Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, 08544, New Jersey, USA

    Adrian M. Price-Whelan

  12. Rudolf-Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford, OX1 3NP, UK

    Ralph Schönrich

  13. Korea Astronomy and Space Science Institute, Daejon, 34055, South Korea

    Andrew Gould

  14. Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, 43210, Ohio, USA

    Andrew Gould

Authors
  1. Maria Bergemann
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Contributions

This project was led by M.B. and initiated by B.S. and K.V.J. The photometric selection of targets was made by B.S., T.S.L. and A.S. The high-resolution Keck spectra were obtained by J.G.C. The VLT proposal to observe the TriAnd star was prepared by B.S. Spectroscopic analysis of the spectra, including stellar parameters and chemical abundances, was carried out by M.B. L.C. measured stellar effective temperatures and A.M.S. carried out the Bayesian analysis of distances. C.F.P.L. provided the N-body simulation that describes the interaction of the Sagittarius galaxy with the Galactic disk. R.S. performed the analysis of stellar kinematics. A.M.P.-W. helped with interpretation of the results and comparison with the models. The manuscript was written mainly by M.B. and A.G. All authors contributed to the text and provided comments.

Corresponding author

Correspondence to Maria Bergemann.

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Extended data figures and tables

Extended Data Figure 1 Chemical abundances of the observed stars.

a, b, Chemical abundance ratios [Mg/Fe] (a) and [Ti/Fe] (b), plotted against metallicity ([Fe/H]), in the TriAnd and A13 overdensities, as well as in Milky Way disk and halo stars; the Fornax and Sagittarius (Sgr) dwarf spheroidal galaxies (dSph); open clusters in the Galactic outer disk; and globular clusters (with error bars reflecting intracluster abundance variation, derived as the r.m.s. variance of the sample, with N = 13 for the M3 cluster and N = 25 for M71). Source data are provided in Extended Data Tables 1 and 3.

Source data

Extended Data Figure 2 Comparison of the observed spectrum of elemental abundances and a model spectrum for a star in the A13 overdensity.

Shown are the Keck spectrum of the star 2MASS 07154242+6704006 (grey dots) and the best-fit model spectrum (red line). We used the Na i lines at 6,154 Å and 6,160 Å to determine the Na abundance of the star.

Source data

Extended Data Figure 3 Line-of-sight velocities (vlos) of the observed stars, plotted against Galactic longitude (l).

GSR, Galactic standard of rest. See Methods for further details.

Extended Data Table 1 Coordinates and 2MASS photometric magnitudes of the observed stars
Full size table
Extended Data Table 2 Radial velocities, stellar parameters and distances of the observed stars
Full size table
Extended Data Table 3 Chemical abundances of oxygen, magnesium, sodium, titanium, europium and barium in the observed stars
Full size table

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Bergemann, M., Sesar, B., Cohen, J. et al. Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk. Nature 555, 334–337 (2018). https://doi.org/10.1038/nature25490

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