Top panel: luminosity of the He II line as a function of the redshift for the 39 identified He II emitters in our sample. The blue circles, red diamonds, black triangles, and green stars represent the reliable emitters with narrow He II lines, the reliable emitters with broad He II lines, the possible emitters, and the objects classified as AGN, respectively. The three axes on the right represent the star-formation rates needed to produce these He II luminosities for a top-heavy IMF with Salpeter slope extending from 1 M⊙ to 500 s M⊙ with metallicities Z = 0 (black), Z = 10-7 (red), and Z = 10-5 (blue), using the conversion in Schaerer (2003) (see text). Bottom panel: redshift distribution of the 39 He II emitters (empty histogram) and of the reliable ones (filled histogram).
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