GALEX far-UV color selection of UV-bright high-redshift quasars

Abstract

We study the small population of z>2.7 quasars detected by GALEX, whose far-UV emission is not extinguished by intervening HI Lyman limit systems. These quasars are of particular importance to detect intergalactic HeII absorption along their sightlines. We correlate verified z>2.7 quasars to the GALEX GR4 source catalog, yielding 304 S/N>3 sources. However, ~50% of these are only detected in the GALEX NUV band, signaling the truncation of the FUV flux by low-redshift Lyman limit systems. We exploit the GALEX UV color to cull the most promising targets for follow-up studies, with blue (red) GALEX colors indicating transparent (opaque) sightlines. Monte Carlo simulations indicate a HeII detection rate of ~60% for quasars with FUV-NUV<1 at z<3.5, a ~50% increase over GALEX searches that do not include color information. We regard 52 quasars detected at S/N>3 to be most promising for HST follow-up, with an additional 114 quasars if we consider S/N>2 detections in the FUV. SDSS provides just half of the NUV-bright quasars that should have been detected by SDSS & GALEX. We revise the SDSS quasar selection function, finding that SDSS systematically misses quasars with blue u-g<2 colors at 3<z<3.5 due to overlap with the stellar locus in color space. Our color-dependent SDSS selection function naturally explains the inhomogeneous u-g color distribution of SDSS quasars with redshift and the color difference between color-selected and radio-selected SDSS quasars. Moreover, it yields excellent agreement between the observed and the predicted number of UV-bright SDSS quasars. We confirm our previous claims that SDSS preferentially selects 3<z<3.5 quasars with intervening HI Lyman limit systems. Our results imply that broadband optical color surveys for 3<z<3.5 quasars have likely underestimated their space density by selecting IGM sightlines with an excess of strong HI absorbers.

22 pages, 17 figures, accepted for publication in ApJ. Figure 1 replaced and Section 2 expanded, Tables 3 and 4 included, conclusions unchanged

References in corpus (26)

• The Sloan Digital Sky Survey Quasar Catalog V. Seventh Data Release
• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• The Sloan Digital Sky Survey Quasar Catalog IV. Fifth Data Release
• HeII Reionization and its Effect on the IGM
• A Direct Precision Measurement of the Intergalactic Lyman-alpha Opacity at 2<z<4.2
• The Evolution of Lyman Limit Absorption Systems to Redshift Six
• A Definitive Survey for Lyman Limit Systems at z~3.5 with the Sloan Digital Sky Survey
• An improved measurement of the flux distribution of the Ly-alpha forest in QSO absorption spectra: the effect of continuum fitting, metal contamination and noise properties
• Physical Properties, Baryon Content, and Evolution of the LyαForest: New Insights from High Resolution Observations at z < 0.4
• Voigt Profile Fitting to Quasar Absorption Lines: An Analytic Approximation to the Voigt-Hjerting Function
• The Keck+Magellan Survey for Lyman Limit Absorption I: The Frequency Distribution of Super Lyman Limit Systems
• An unbiased measurement of the UV background and its evolution via the proximity effect in quasar spectra
• A Monte Carlo simulation of the intergalactic absorption and the detectability of the Lyman continuum from distant galaxies
• Statistical Properties of the GALEX/SDSS matched source catalogs, and classification of the UV sources
• The UV spectrum of HS1700+6416 II. FUSE observations of the HeII Lyman alpha forest
• Reionisation scenarios and the temperature of the IGM
• Photo-heating and the fate of hard photons during the reionisation of HeII by quasars
• The Evolution of Lyman alpha Absorbers in the Redshift Range 0.5<z<1.9
• GALEX-SDSS Catalogs for Statistical Studies
• Continuous statistics of the Lyman-alpha forest at 0 < z < 1.6: the mean flux, flux distribution, and autocorrelation from HST FOS spectra
• The Faint End of the Quasar Luminosity Function at z~4
• Spectral shape of the UV ionizing background and HeII absorption at redshifts 1.8 < z < 2.9
• Fluctuations in the Ionizing Background During and After Helium Reionization
• A High Yield of New Sightlines for the Study of Intergalactic Helium: Far-UV-Bright Quasars from SDSS, GALEX, and HST
• Fluctuations of the intergalactic UV background towards two lines of sight
• Deep GALEX Observations of the Coma Cluster: Source Catalog and Galaxy Counts

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