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Reddened Quasars


A search for quasars reddened by dust absorption (either from intervening sources or sources local to the quasar) in the 220-square-degree survey area of Stripe 82.

Finding Targets

An object whose ANCILLARY_TARGET1 value includes 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 Target Description
RQSS_SF 32 Selected from SDSS and FIRST photometry
RQSS_SFC 33 Selected from SDSS and FIRST photometry (child object in SDSS imaging)
RQSS_STM 34 Selected from SDSS and 2MASS photometry
RQSS_STMC 35 Selected from SDSS and 2MASS photometry (child object in SDSS imaging)


Quasar candidates likely to be intrinsically reddened - quasar candidates with E(B-V) > 0.5 - were selected from SDSS photometry complemented by photometry from either the Faint Images of the Radio Sky at Twenty-one centimeters (FIRST; Gregg et al. 1996) or the Two Micron All-Sky Survey (2MASS; Skrutskie et al. 2006). The goal of observing these reddened quasars was to better determine the distribution of reddenings, both in intervening absorbers and at quasar redshifts - which in turn enables studies of reddening as a function of quasar properties.

Targets were selected based on color selection and stellar morphology. All targets were required to have 17 < zPSF < 21, with dereddened colors satisfying the equation (gPSF - iPSF) - 3σ(gPSF - iPSF) > 0.9.

Targets selected from SDSS plus FIRST data were denoted by sub-programs RQSS_SF or RQSS_SFC (the trailing C indicates that the target was a CHILD object in SDSS), and were additionally required to match within 2" of a FIRST source. Targets selected from SDSS plus 2MASS data (sub-programs RQSS_TM or RQSS_TMC) were additionally required to match within 3" of a 2MASS source having 11 < K < 15.1, (J - K) > 1.25, and a 7-dimensional color distance (Covey et al. 2007) greater than 50 (this is the distance in units of χ2 to the point on the stellar locus with the same (g – i) color as the object).

This ancillary target program was discontinued after the first year due to low yield, and targets are included on only 13 completed plates. It is superseded by the ancillary target program K-band Limited Sample of Quasars.

Primary contact

Pat Hall
York University
phall -at-


Covey, K. R., et al. 2007, AJ, 134, 2398
Gregg, M.D., Becker, R.H., White, R.L., Helfand, D.J., McMahon, R.G., Hook, I.M., 1996, AJ, 112, 407, doi:10.1086/118024
Skrutskie, M. F., et al. 2006, AJ, 131, 1163