Extreme UV QSOs
  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$<$2.6. For the low
redshift objects, the "blue" FUV-NUV color may be caused by enhanced Ly$\alpha$
emission, since Ly$\alpha$ transits the GALEX FUV band from z=0.1 to z=0.47.
Synthetic QSO templates constructed with Ly$\alpha$ up to 3 times stronger than
in standard templates match the observed UV colors of our low redshift sample.
The H$\alpha$ 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$\alpha$ 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
