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Extremely metal-poor gas at a redshift of 7

Simcoe, Robert A. and Sullivan, Peter W. and Cooksey, Kathy L. and Kao, Melodie M. and Matejek, Michael S. and Burgasser, Adam J. (2012) Extremely metal-poor gas at a redshift of 7. Nature, 492 (7427). pp. 79-82. ISSN 0028-0836. doi:10.1038/nature11612.

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In typical astrophysical environments, the abundance of heavy elements ranges from 0.001 to 2 times the solar value. Lower abundances have been seen in selected stars in the Milky Way’s halo and in two quasar absorption systems at redshift z = 3 (ref. 4). These are widely interpreted as relics from the early Universe, when all gas possessed a primordial chemistry. Before now there have been no direct abundance measurements from the first billion years after the Big Bang, when the earliest stars began synthesizing elements. Here we report observations of hydrogen and heavy-element absorption in a spectrum of a quasar at z =  7.04, when the Universe was just 772 million years old (5.6 per cent of its present age). We detect a large column of neutral hydrogen but no corresponding metals (defined as elements heavier than helium), limiting the chemical abundance to less than 1/10,000 times the solar level if the gas is in a gravitationally bound proto-galaxy, or to less than 1/1,000 times the solar value if it is diffuse and unbound. If the absorption is truly intergalactic, it would imply that the Universe was neither ionized by starlight nor chemically enriched in this neighbourhood at z ≈ 7. If it is gravitationally bound, the inferred abundance is too low to promote efficient cooling, and the system would be a viable site to form the predicted but as yet unobserved massive population III stars.

Item Type:Article
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URLURL TypeDescription DOIArticle ReadCube access Paper
Simcoe, Robert A.0000-0003-3769-9559
Kao, Melodie M.0000-0001-5125-1414
Burgasser, Adam J.0000-0002-6523-9536
Additional Information:© 2012 Nature Publishing Group. Received 20 March 2012; Accepted 19 September 2012; Published online 05 December 2012. We thank J. O’Meara and A. Frebel for comments during the preparation of this Letter. M. Haehnelt also provided advice on methods for modelling the quasar near-zone, and G. Richards shared his composite QSO spectra in electronic form. This work includes data gathered with the 6.5-m Magellan Telescopes located at Las Campanas Observatory, Chile. R.A.S. acknowledges support from the NSF under awards AST-0908920 and AST-1109115. K.L.C. is supported by the NSF Astronomy and Astrophysics Postdoctoral Fellowship programme. Author Contributions: R.A.S. constructed the FIRE instrument, and together with P.W.S. designed and executed the observations, performed the analysis and prepared the manuscript. K.L.C. prepared observations and edited the manuscript. M.S.M. assisted with the pipeline software used to reduce the spectroscopic data, and M.M.K. wrote the software to perform eigenspectrum continuum fits. A.J.B. contributed to the spectrograph construction, and executed observations for the program. All authors helped with the scientific interpretations and commented on the manuscript.
Funding AgencyGrant Number
NSF Astronomy and Astrophysics FellowshipUNSPECIFIED
Subject Keywords:Astronomy; Physics
Issue or Number:7427
Record Number:CaltechAUTHORS:20130103-084223576
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36134
Deposited By: Tony Diaz
Deposited On:10 Jan 2013 19:25
Last Modified:09 Nov 2021 23:20

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