6/14/2023 0 Comments Sdss astrometry![]() ![]() The resulting spectral energy distributions (SEDs) cover ∼350-9000 Å (rest frame), where the overall median SED peaks near the Lyα emission line, as found in other UV quasar studies. The UV-detected quasars are well separated from stars in UV-optical color-color space, with the UV-optical relative colors suggesting a marginally detected population of reddened objects due to absorption along the line of sight or dust associated with the quasar. The GALEX positions are shown to be consistent with the SDSS astrometry to within an rms scatter of 0.6″-0.7″ in each coordinate, and the empirically determined photometric errors from multiepoch GALEX observations significantly exceed the Poissonian errors quoted in the GR1 object catalogs. Statistical tests performed on the distributions of nondetections indicate that the optically selected quasars missed in the UV tend to be optically faint or at high redshift. ![]() Most of the DR3 sample quasars are detected in the near-UV until z ∼ 1.7, with the near-UV detection fraction dropping to ∼50% by z ∼ 2. Of the 6371 SDSS DR3 quasars covered by 204 GALEX GR1 tiles, 5380 (84%) have near-UV detections, while 3034 (48%) have both near-UV and far-UV detections using a matching radius of 7″. We present an analysis of the broadband UV and optical properties of z ≲ 3.4 quasars matched in the Galaxy Evolution Explorer (GALEX) General Data Release 1 (GR1) and the Sloan Digital Sky Survey (SDSS) Data Release 3 (DR3). ![]()
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