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 \approx 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 ( \sim 85 \% ) of the SDSS objects were not matched simply because there were not covered by the ULAS .
The positional standard deviation of the SDSS Quasar to ULAS matches is \delta _ { R . A . } = 0.1370 ^ { \prime \prime } and \delta _ { Decl . } = 0.1314 ^ { \prime \prime } .
We find an absolute systematic astrometric offset between the SDSS Quasar catalog and the UKIDSS LAS , of | { R . A . _ { offset } } | = 0.025 ^ { \prime \prime } , and | { Decl . _ { offset } } | = 0.040 ^ { \prime \prime } ; we suggest the nature of this offset to be due to the matching of catalog , rather than image , level data .
Our matched catalog has a surface density of \approx 53 deg ^ { -2 } for K \leq 18.27 objects ; tests using our matched catalog , along with data from the UKIDSS DXS , implies that our limiting magnitude is i \approx 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 \lesssim 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 .