Y. Izotov, G. Stasinska, und N. Guseva. (2013)cite arxiv:1308.2100Comment: 23 pages, 14 figures, accepted for publication in Astronomy and Astrophysics.
J. Howk, N. Lehner, B. Fields, und G. Mathews. (2012)cite arxiv:1207.3081Comment: To appear in Nature. Includes main text and Supplementary Information.