Extreme UV QSOs

Abstract

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

Astronomical Journal, in press

References in corpus (8)

• The Galaxy Evolution Explorer: A Space Ultraviolet Survey Mission
• A Physical Model for the Co-evolution of QSOs and of their Spheroidal Hosts
• The Rest-Frame Extreme Ultraviolet Spectral Properties of QSOs
• Quasars and the Big Blue Bump
• Statistical Properties of the GALEX/SDSS matched source catalogs, and classification of the UV sources
• Environments of QSOs at Redshifts 0.9 to 1.3
• The unusual UV continuum of quasar Ton 34 and the possibility of crystalline dust absorption
• QSOs in the combined SDSS/GALEX database

Cited by in corpus (12)

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• The Ultraviolet Sky: An Overview from the GALEX Surveys
• Catalogs of Hot White Dwarfs in the Milky Way from GALEX's Ultraviolet Sky Surveys. Constraining Stellar Evolution
• The Canada-France Imaging Survey: First results from the u-band component
• GALEX observations of quasar variability in the ultraviolet
• Matched photometric catalogs of GALEX UV sources with Gaia DR2 and SDSS DR14 databases (GUVmatch)
• Catalog of Planetary Nebulae detected by GALEX and corollary optical surveys
• Interesting Features in the Combined GALEX and Sloan Color Diagrams of Solar-like Galactic Populations
• Detecting Variability in Massive Astronomical Time-Series Data II: Variable Candidates in the Northern Sky Variability Survey
• The Next Generation Virgo Cluster Survey. XXVIII. Characterization of the Galactic White Dwarf Population
• Hot white dwarf candidates from the IGAPS-GALEX cross-match
• Hot Stars in the GALEX Ultraviolet Sky Surveys (GUVcat_AISxSDSS_HS) and the Binary Fraction of Hot Evolved Stars