极端UV类星体
Extreme UV QSOs
摘要：
我们提出了一个样本的光谱证实类星体的FUV-NUV颜色（GALEX测光测量）比典型的类星体模板，比大多数已知的类星体蓝。我们分析了它们的FUV到NIR颜色、光度和光谱。该样本包括一组150个低红移（z $<$ 0.5）的天体，以及一组21个红移为1.7 $<$ z $<$ 2.6的天体。对于低红移天体，“蓝色”FUV-NUV颜色可能是由增强的Ly $α$发射引起的，因为Ly $α$从z=0.1到z=0.47穿过GALEX FUV带。合成类星体模板构建与赖氨酸$α$高达3倍强于标准模板匹配我们的低红移样品的紫外线颜色。H $α$发射增加，并且随着绝对UV光度的增加，光谱变得更蓝。红移约为2的紫外-蓝色类星体，其中GALEX带的样本重帧约为450- 590 A（FUV）和约590- 940 A（NUV），比在NUV中类似红移的紫外-正常类星体的平均值要暗，而它们在其他波段的光度相当。因此，我们推测，他们观察到的FUV-NUV颜色可能是由陡峭的通量上升到短波长和低于莱曼极限的尘埃吸收，如小颗粒或结晶碳的组合来解释。可以在10个天体中测量到Ly $α$与CIV的比值;它高于（平均30%）紫外正常类星体，接近于冲击或碰撞电离的预期值。完整版本可从供应商网站获得：http://dolomiti.pha.jhu.edu/papers/2009_AJ_Extreme_UV_QSOs.pdf
英文摘要：
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$<$2.6. For the low redshift objects, the "blue" FUV-NUV color may be caused by enhanced Ly$α$ emission, since Ly$α$ transits the GALEX FUV band from z=0.1 to z=0.47. Synthetic QSO templates constructed with Ly$α$ up to 3 times stronger than in standard templates match the observed UV colors of our low redshift sample. The H$α$ 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 Ly$α$ 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. FULL VERSION AVAILABLE FROM AUTHOR'S WEB SITE: http://dolomiti.pha.jhu.edu/papers/2009_AJ_Extreme_UV_QSOs.pdf
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