Abstract
Models of the chemical evolution of the Milky Way suggest that the observed abundances of elements heavier than helium (‘metals’) require a continuous infall of gas with metallicity (metal abundance) about 0.1 times the solar value. An infall rate integrated over the entire disk of the Milky Way of ∼1 solar mass per year can solve the ‘G-dwarf problem’—the observational fact that the metallicities of most long-lived stars near the Sun lie in a relatively narrow range1,2,3. This infall dilutes the enrichment arising from the production of heavy elements in stars, and thereby prevents the metallicity of the interstellar medium from increasing steadily with time. However, in other spiral galaxies, the low-metallicity gas needed to provide this infall has been observed only in associated dwarf galaxies4 and in the extreme outer disk of the Milky Way5,6. In the distant Universe, low-metallicity hydrogen clouds (known as ‘damped Lyα absorbers’) are sometimes seen near galaxies7,8. Here we report a metallicity of 0.09 times solar for a massive cloud that is falling into the disk of the Milky Way. The mass flow associated with this cloud represents an infall per unit area of about the theoretically expected rate, and ∼0.1–0.2 times the amount required for the whole Galaxy.
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References
Van den Bergh,S. The frequency of stars with different metal abundances. Astron. J. 67, 486–490 (1962).
Giovagnoli,A. & Tosi,M. Chemical evolution models with a new stellar nucleosynthesis. Mon. Not. R. Astron. Soc. 273, 499–504 (1995).
Pagel,B. E. J. Nucleosynthesis and Chemical Evolution of Galaxies (Cambridge Univ. Press, 1997).
Skillman,E. D., Bomans,D. J. & Kobulnicky,H. A. Interstellar medium abundances in the Pegasus dwarf irregular galaxy. Astrophys. J. 474, 205–216 (1997).
Rudolph,A. L., Simpson,J. P., Haas,M. R., Erickson,E. F. & Fich,M. Far-infrared abundance measurements in the outer galaxy. Astrophys. J. 489, 94–101 (1997).
Ferguson,A. M. N., Gallagher,J. S. & Wyse,R. F. G. The extreme outer regions of disk galaxies. I. Chemical abundances of HII regions. Astron. J. 116, 673–690 (1998).
Lu,L., Sargent,W. L. W. & Barlow,T. A. The N/Si abundance ratio in 15 damped Lyα galaxies: implications for the origin of nitrogen. Astron. J. 115, 55–61 (1998).
Pettini,M., Ellison,S. L., Steidel,C. C. & Bowen,D. V. Metal abundances at z < 1.5: fresh clues to the chemical enrichment history of damped Lyα systems. Astrophys. J. 510, 576–589 (1999).
Wakker,B. P. & van Woerden,H. High-velocity clouds. Annu. Rev. Astron. Astrophys. 35, 217–266 (1997).
Savage,B. D. & Sembach,K. R. Interstellar abundances from absorption-line observations with the Hubble Space Telescope. Annu. Rev. Astron. Astrophys. 34, 279–329 (1996).
Lu,L. et al. The metallicity and dust content of HVC 287.5 + 22.5 + 240: evidence for a Magellanic Clouds origin. Astron. J. 115, 162–167 (1998).
Reynolds,R. J., Tufte,S. L., Haffner,L. M., Jaehnig,K. & Percival,J. W. The Wisconsin H-alpha Mapper (WHAM): A brief review of performance characteristics and early scientific results. Publ. Astron. Soc. Aust. 15, 14–18 (1998).
Hartmann,D. & Burton,W. B. Atlas of Galactic Neutral Hydrogen (Cambridge Univ. Press, 1997).
Wakker,B. P. et al. in Stromlo Workshop on High-velocity Clouds (eds Gibson, B. K. & Putman, M. E.) 26–37 (ASP Conf. Ser. 166, Astronomical Soc. of the Pacific, San Francisco, 1999).
Anders,E. & Grevesse,N. Abundances of the elements—Meteoritic and solar. Geochim. Cosmochim. Acta 53, 197–214 (1989).
van Woerden,H., Peletier,R. F., Schwarz,U. J., Wakker,B. P. & Kalberla,P. M. W. in Stromlo Workshop on High-velocity Clouds (eds Gibson, B. R. & Putman, M. E.) 1–25 (ASP Conf. Ser. 166, Astronomical Soc. of the Pacific, San Francisco, 1999).
van Woerden,H., Schwarz,U. J., Peletier,R. F., Wakker,B. P. & Kalberla,P. M. W. A confirmed location in the Galactic halo for the high-velocity cloud ‘Chain A’. Nature 400, 138–141 (1999).
Snowden,S. L., Egger,R., Finkbeiner,D. P., Freyberg,M. J. & Plucinsky,P. P. Progress on establishing the spatial distribution of material responsible for the 1/4 kev soft x-ray diffuse background local and halo components. Astrophys. J. 493, 715–729 (1998).
Wolfire,M. G., McKee,C. F., Hollenbach,D. & Tielens,A. G. G. M. The multiphase structure of the galactic halo: high-velocity clouds in a hot corona. Astrophys. J. 453, 673–684 (1995).
Wakker,B. P., Murphy,E. M., van Woerden,H. & Dame,T. M. A sensitive search for molecular gas in high-velocity clouds. Astrophys. J. 488, 216–223 (1997).
Bregman,J. N. The galactic fountain of high-velocity clouds. Astrophys. J. 236, 577–591 (1980).
Blitz,L., Spergel,D., Teuben,P., Hartmann,D. & Burton,W. B. High velocity clouds: building blocks of the Local Group. Astrophys. J. 514, 818–843 (1999).
Zwaan,M. A., Briggs,F. H., Sprayberry,D. & Sorar,E. The HI mass function of galaxies from a deep survey in the 21-cm line. Astrophys. J. 490, 173–186 (1997).
Oort,J. H. The formation of galaxies and the origin of the high velocity hydrogen. Astron. Astrophys. 7, 381–404 (1970).
Yanny,B. & York,D. G. Emission-line objects near quasi-stellar object absorbers. III Clustering and colors of moderate redshift HII regions. Astrophys. J. 391, 569–576 (1992).
Gardiner,L. T. & Noguchi,M. N-body simulations of the Small Magellanic Cloud and the Magellanic Stream. Mon. Not. R. Astron. Soc. 278, 191–208 (1996).
Haffner,L. M., Reynolds,R. J. & Tufte,S. L. WHAM observations of Hα, SII, and NII toward the Perseus Arm: probing the physical conditions of the WIM. Astrophys. J. 523, 223–233 (1999).
Verner,D. A., Barthel,P. D. & Tytler,D. Atomic data for absorption lines from the ground level at wavelengths greater than 228 Å. Astron. Astrophys. 108, 287–340 (1994).
Wakker,B. P., van Woerden,H., Schwarz,U. J., Peletier,R. F. & Douglas,N. G. The Ca+ abundance of HVC complex C. Astron. Astrophys. 306, L25–L28 (1996).
Acknowledgements
This work was supported by the Space Telescope Science Institute. The Hubble Space Telescope is operated by the Association of Universities for Research in Astronomy, Inc. The Effelsberg Telescope belongs to the Max Planck Institute for Radio Astronomy in Bonn. The Westerbork Radio Observatory is operated by the Netherlands Foundation for Research in Astronomy (ASTRON/NFRA) with financial support from NWO.
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Wakker, B., Howk, J., Savage, B. et al. Accretion of low-metallicity gas by the Milky Way. Nature 402, 388–390 (1999). https://doi.org/10.1038/46498
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DOI: https://doi.org/10.1038/46498
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