The age of the Milky Way inner halo

  • A Corrigendum to this article was published on 11 July 2012

Abstract

The Milky Way galaxy has several components, such as the bulge, disk and halo. Unravelling the assembly history of these stellar populations is often restricted because of difficulties in measuring accurate ages for low-mass, hydrogen-burning stars1,2. Unlike these progenitors, white dwarf stars3, the ‘cinders’ of stellar evolution, are remarkably simple objects and their fundamental properties can be measured with little ambiguity4,5. Here I report observations of newly formed white dwarf stars in the halo of the Milky Way, and a separate analysis of archival data in the well studied 12.5-billion-year-old globular cluster Messier 4. I measure the mass distribution of the remnant stars and invert the stellar evolution process to develop a mathematical relation that links this final stellar mass to the mass of their immediate progenitors, and therefore to the age of the parent population. By applying this technique to a small sample of four nearby and kinematically confirmed halo white dwarf stars, I calculate the age of local field halo stars to be 11.4 ± 0.7 billion years. The oldest globular clusters formed 13.5 billion years ago. Future observations of newly formed white dwarf stars in the halo could be used to reduce the uncertainty, and to probe relative differences between the formation times of the youngest globular clusters and the inner halo.

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Figure 1: Spectroscopic examination of white dwarfs in Messier 4 and the Milky Way halo.
Figure 2: The remnant mass and population age of the Milky Way halo.

References

  1. 1

    Soderblom, D. R. The ages of stars. Annu. Rev. Astron. Astrophys. 48, 581–629 (2010)

    ADS  Article  Google Scholar 

  2. 2

    Jofré, P. & Weiss, A. The age of the Milky Way halo stars from the Sloan Digital Sky Survey. Astron. Astrophys. 533, A59 (2011)

    ADS  Article  Google Scholar 

  3. 3

    Paczyński, B. Evolution of single stars. I. Stellar evolution from main sequence to white dwarf or carbon ignition. Acta Astron. 20, 47–58 (1970)

    ADS  Google Scholar 

  4. 4

    Wegner, G. & Schulz, H. Spectroscopy of suspected peculiar DA white dwarfs. I—Equivalent widths and line profiles. Astron. Astrophys. 43 (Suppl.). 473–478 (1981)

    ADS  CAS  Google Scholar 

  5. 5

    Bergeron, P., Saffer, R. A. & Liebert, J. A spectroscopic determination of the mass distribution of DA white dwarfs. Astrophys. J. 394, 228–247 (1992)

    ADS  Article  Google Scholar 

  6. 6

    Bedin, L. R. et al. The end of the white dwarf cooling sequence in M4: an efficient approach. Astrophys. J. 697, 965–979 (2009)

    ADS  Article  Google Scholar 

  7. 7

    Kalirai, J. S. et al. A deep, wide-field, and panchromatic view of 47 Tuc and the SMC with HST: observations and data analysis methods. Astron. J. 143, 11 (2012)

    ADS  Article  Google Scholar 

  8. 8

    Dotter, A. et al. The ACS survey of galactic globular clusters. IX. Horizontal branch morphology and the second parameter phenomenon. Astrophys. J. 708, 698–716 (2010)

    ADS  CAS  Article  Google Scholar 

  9. 9

    Dotter, A. et al. The Dartmouth Stellar Evolution Database. Astrophys. J. 178 (Suppl.). 89–101 (2008)

    CAS  Article  Google Scholar 

  10. 10

    Shapiro, S. L. & Teukolsky, S. A. Black Holes, White Dwarfs, and Neutron Stars: The Physics of Compact Objects 663 (Wiley-Interscience, 1983)

    Google Scholar 

  11. 11

    Tremblay, P.-E. & Bergeron, P. Spectroscopic analysis of DA white dwarfs: Stark broadening of hydrogen lines including nonideal effects. Astrophys. J. 696, 1755–1770 (2009)

    ADS  Article  Google Scholar 

  12. 12

    Renzini, A. & Fusi Pecci, F. Tests of evolutionary sequences using color-magnitude diagrams of globular clusters. Annu. Rev. Astron. Astrophys. 26, 199–244 (1988)

    ADS  CAS  Article  Google Scholar 

  13. 13

    Moehler, S. et al. Spectral types and masses of white dwarfs in globular clusters. Astron. Astrophys. 420, 515–525 (2004)

    ADS  Article  Google Scholar 

  14. 14

    Oppenheimer, B. R. et al. Direct detection of galactic halo dark matter. Science 292, 698–702 (2001)

    ADS  CAS  Article  Google Scholar 

  15. 15

    Gates, E. et al. Discovery of new ultracool white dwarfs in the Sloan Digital Sky Survey. Astrophys. J. 612, L129–L132 (2004)

    ADS  Article  Google Scholar 

  16. 16

    Kilic, M. et al. Visitors from the halo: 11 Gyr old white dwarfs in the solar neighborhood. Astrophys. J. 715, L21–L25 (2010)

    ADS  CAS  Article  Google Scholar 

  17. 17

    Napiwotzki, R. et al. Search for progenitors of supernovae type Ia with SPY. Astron. Nachr. 322, 411–418 (2001)

    ADS  CAS  Article  Google Scholar 

  18. 18

    Pauli, E.-M. et al. 3D kinematics of white dwarfs from the SPY project. II. Astron. Astrophys. 447, 173–184 (2006)

    ADS  Article  Google Scholar 

  19. 19

    Kalirai, J. S. et al. Stellar evolution in NGC 6791: mass loss on the red giant branch and the formation of low-mass white dwarfs. Astrophys. J. 671, 748–760 (2007)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Kalirai, J. S. et al. The initial-final mass relation: direct constraints at the low-mass end. Astrophys. J. 676, 594–609 (2008)

    ADS  CAS  Article  Google Scholar 

  21. 21

    Kalirai, J. S. et al. The masses of population II white dwarfs. Astrophys. J. 705, 408–425 (2009)

    ADS  CAS  Article  Google Scholar 

  22. 22

    Sarajedini, A. et al. The ACS survey of galactic globular clusters. I. Overview and clusters without previous Hubble Space Telescope photometry. Astron. J. 133, 1658–1672 (2007)

    ADS  Article  Google Scholar 

  23. 23

    Dotter, A., Sarajedini, A. & Anderson, J. Globular clusters in the outer galactic halo: new Hubble Space Telescope/Advanced Camera for Surveys imaging of six globular clusters and the galactic globular cluster age-metallicity relation. Astrophys. J. 738, 74 (2011)

    ADS  Article  Google Scholar 

  24. 24

    Carollo, D. et al. Two stellar components in the halo of the Milky Way. Nature 450, 1020–1025 (2007)

    ADS  CAS  Article  Google Scholar 

  25. 25

    Beers, T. C. et al. The case for the dual halo of the Milky Way. Astrophys. J. 746, 34 (2012)

    ADS  Article  Google Scholar 

  26. 26

    Zolotov, A. et al. The dual origin of stellar halos. Astrophys. J. 702, 1058–1067 (2009)

    ADS  CAS  Article  Google Scholar 

  27. 27

    Font, A. S. et al. Cosmological simulations of the formation of the stellar haloes around disc galaxies. Mon. Not. R. Astron. Soc. 416, 2802–2820 (2011)

    ADS  Article  Google Scholar 

  28. 28

    Tremblay, P.-E., Bergeron, P. & Gianninas, A. An improved spectroscopic analysis of DA white dwarfs from the Sloan Digital Sky Survey Data Release 4. Astrophys. J. 730, 128 (2011)

    ADS  Article  Google Scholar 

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Acknowledgements

The data presented in this paper were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. I acknowledge the significant cultural role and reverence that the summit of Mauna Kea has within the indigenous Hawaiian community. I am fortunate to have had the opportunity to conduct observations from this mountain. This work was also based on observations obtained at the Paranal Observatory of the European Southern Observatory. I thank A. Dotter, P. Bergeron, and P.-E. Tremblay for discussions related to stellar evolution and ages. I also thank U. Heber for providing us reduced spectra from the SPY Survey.

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Correspondence to Jason S. Kalirai.

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Kalirai, J. The age of the Milky Way inner halo. Nature 486, 90–92 (2012). https://doi.org/10.1038/nature11062

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