Near Infrared Photometric properties of 130,000 Quasars: An SDSS-UKIDSS
  matched catalog
  We present a catalog of over 130,000 quasars candidates with NIR photometric
properties, with an areal coverage of approximately 1,200 deg^2. This is
achieved by matching the Sloan Digital Sky Survey (SDSS) in the optical ugriz
bands, to the UKIRT Infrared Digital Sky Survey (UKIDSS) Large Area Survey
(LAS) in the near-infrared YJHK bands. We match the ~1 million SDSS DR6
Photometric Quasar catalog to Data Release 3 of the UKIDSS LAS (ULAS), and
produce a catalog with 130,827 objects with detections in one or more NIR
bands, of which 74,351 objects have optical and K-band detections and 42,133
objects have the full 9-band photometry. The majority ~85 of the SDSS objects
were not matched simply because there were not covered by the ULAS. Our matched
catalog has a surface density of ~53 deg^-2 for K >18.27 objects; tests using
our matched catalog, along with data from the UKIDSS DXS, implies that our
limiting magnitude is i ~ 20.6. Color-redshift diagrams, for the optical and
NIR, show the close agreement between our matched catalog and recent quasar
color models at redshift z > 2.0, while at higher redshifts, the models
generally appear to be bluer than the mean observed quasar colors. The gJK and
giK color-spaces are used to examine methods of differentiating between stars
and (mid-redshift) quasars, key to currently ongoing quasar surveys. Finally,
we report on the NIR photometric properties of high, z>4.6, and very high,
z>5.7, redshift previously discovered quasars.
