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K-Band Selected Sample of Quasars


Quasar candidates in the 220-square-degree footprint of Stripe 82 that were selected by matching SDSS and UKIDSS photometry

Finding Targets

An object whose ANCILLARY_TARGET2 value include one or more of the bitmasks in the following table was targeted for spectroscopy as part of this ancillary target program. See SDSS-III bitmasks to learn how to use these values to identify objects in this ancillary target program.

(bit name)
Bit in ANCILLARY_TARGET2 Target Description Target density
KQSO_BOSS 2 Quasars selected from UKIDSS photometry 1


Potential quasars were identified by photometering data from the UKIRT Infrared Deep Sky Survey (UKIDSS) at the position of SDSS sources to a limiting magnitude KAB < 19.0 (KVega < 17.1). The goal of this ancillary target program was to identify highly red and reddened quasars that would have been missed by the main BOSS Quasar Target Selection algorithms. The sample described here allows investigations of, for example, the incidence of broad absorption line (BAL) quasars, or of highly reddened gravitationally-lensed quasars.

This ancillary target program superseded the Reddened Quasars target selection program, since the superior UKIDSS photometry could target red, reddened, and high-redshift quasars better than 2MASS photometry. In addition, the color cut of (uPSF - gPSF) > 0.4 used here better complemented the BOSS mission to target mostly higher-redshift quasars.

The targets not included in Stripe 82 were effectively incorporated into the BONUS sample through the XDQSO target selection (Bovy et al. 2011, Bovy et al. 2012); therefore, this ancillary program will not be continued for the remainder of the BOSS footprint.

This ancillary program superseded the ancillary program A Large Sample of Reddened Quasars>, as the superior UKIDSS photometry could better target red, reddened and high redshift quasars than 2MASS. In addition, the cut of (uPSF - gPSF) > 0.4 better complemented the BOSS mission to target mostly higher redshift quasars.

Primary contact

Richard McMahon
University of Cambridge
rgm -at-

Target selection details

In the original selection, approximately 2,000 targets were identified that have (gPSF - iPSF) < 1.153 x (iPSF - K) - 1.401, to avoid the color space locus of the stellar main sequence, and (uPSF - gPSF) > 0.4 to exclude UV-excess quasars (i.e., unreddened quasars at redshifts of about z > 2.15).


Bovy, J., Hennawi, J.F., Hogg, D.W., Myers, A.D., Kirkpatrick, J.A., Schlegel, D.J., Ross, N.P., Sheldon, E.S., McGreer, I.D., Schneider, D.P., & Weaver, B.A., 2011, ApJ, 729, 141, doi:10.1088/0004-637X/729/2/141
Bovy, J., Myers, A.D., Hennawi, J.F., Hogg, D.W., McMahon, R.G., Schiminovich, D., Sheldon, E.S., Brinkmann, J., Schneider, D.P., & Weaver, B.A., 2012, ApJ, 749, 41, doi:10.1088/0004-637X/749/1/41