The Optical and Near-Infrared Properties of 2837 Quasars in the UKIRT Infrared Deep Sky Survey (UKIDSS)

The UKIRT Infrared Deep Sky Survey (UKIDSS) is the first of a new generation of hemispheric imaging projects to extend the work of the Two Micron All Sky Survey (2MASS) by reaching three magnitudes deeper in Y JHK imaging, to K = 18.2 (5�, Vega) over wide fields. Better complementing existing optical surveys such as the Sloan Digital Sky Survey (SDSS), the resulting public imaging catalogues provide new photometry of rare object samples too faint to be reached previously. The first data release of UKIDSS has already surpassed 2MASS in terms of photons gathered, and using this new dataset we examine the near-infrared properties of 2837 quasars found in the SDSS and newly catalogued by the UKIDSS in �189deg 2 . The matched quasars include the RA range 22 h to 4 h on the Southern Equatorial Stripe (SDSS Stripe 82), an area of significant future followup possibilities with deeper surveys and pointed observations. The sample covers the redshift and absolute magnitude ranges 0.08 � z � 5.03 and 29.5 � Mi � 22.0, and 98per cent of SDSS quasars have matching UKIDSS data. We discuss the photometry, astrometry, and various colour properties of the quasars. We also examine the effectiveness of quasar/star separation using the near-infrared passbands. The combination of SDSS ugriz photometry with the Y JHK near-infrared photometry from UKIDSS over large areas of sky has enormous potential for advancing our understanding of the quasar population.