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Extreme UV QSOs
Bianchi, Luciana...

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Extreme UV QSOs by Bianchi, Luciana ( Author )
Lemonjar Open Access
N.A
13-01-2009
We present a sample of spectroscopically confirmed QSOs with FUV-NUV color (as measured by GALEX photometry) bluer than canonical QSO templates and than the majority of known QSOs. We analyze their FUV to NIR colors, luminosities and optical spectra. The sample includes a group of 150 objects at low redshift (z < 0.5), and a group of 21 objects with redshift 1.7<z<2.6. For the low redshift objects, the "blue" FUV-NUV color may be caused by enhanced Lyα emission, since Lyα transits the GALEX FUV band from z=0.1 to z=0.47. Synthetic QSO templates constructed with Lyα up to 3 times stronger than in standard templates match the observed UV colors of our low redshift sample. The Hα emission increases, and the optical spectra become bluer, with increasing absolute UV luminosity. The UV-blue QSOs at redshift about 2, where the GALEX bands sample restframe about 450-590A (FUV) and about 590-940A(NUV), are fainter than the average of UV-normal QSOs at similar redshift in NUV, while they have comparable luminosities in other bands. Therefore we speculate that their observed FUV-NUV color may be explained by a combination of steep flux rise towards short wavelengths and dust absorption below the Lyman limit, such as from small grains or crystalline carbon. The ratio of Lyα to CIV could be measured in 10 objects; it is higher (30% on average) than for UV-normal QSOs, and close to the value expected for shock or collisional ionization.
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Article
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36.88 KB
English
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MYR 0.00
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https://arxiv.org/abs/0901.1896
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