The optical and near‐infrared properties of 2837 quasars in the United Kingdom Infrared Telescope Infrared Deep Sky Survey

The United Kingdom Infrared Telescope (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 YJHK imaging, to K = 18.2 (5σ, 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 the UKIDSS has already surpassed the 2MASS in terms of photons gathered, and using this new data set we examine the near‐infrared (NIR) properties of 2837 quasars found in the SDSS and newly catalogued by the UKIDSS in ∼189 deg 2 . The matched quasars include the right ascension range 22 h –4 h on the Southern Equatorial Stripe (SDSS Stripe 82), an area of significant future follow‐up possibilities with deeper surveys and pointed observations. The sample covers the redshift and absolute magnitude ranges 0.08 ≤ z ≤ 5.03 and −29.5 ≤ M i ≤−22.0 , and 98 per 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 a quasar–star separation using the NIR passbands. The combination of SDSS ugriz photometry with the YJHK NIR photometry from the UKIDSS over large areas of the sky has enormous potential for advancing our understanding of the quasar population.