Near Infrared Photometric properties of 130,000 Quasars: An SDSS-UKIDSS matched catalog

TL;DR

This paper presents a large catalog of over 130,000 quasar candidates with near-infrared photometry, matched from SDSS and UKIDSS surveys, enabling improved quasar identification and redshift analysis.

Contribution

The creation of a comprehensive NIR photometric quasar catalog by matching SDSS and UKIDSS data, providing new insights into quasar colors and redshift distributions.

Findings

High surface density of K >18.27 quasars (~53 deg^-2)

Good agreement between observed quasar colors and models at z > 2.0

Effective methods for star-quasar differentiation using color spaces

Abstract

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.