Exploring z>0.6 LRGs from SDSS and WISE
|University of Pittsburgh|
A spectroscopic survey of distant (z > 0.6) luminous red galaxies (LRGs) selected using WISE photometry, with the goal of better calibrating photometric redshifts of these galaxies, and therefore improving distance estimates
An object whose
ANCILLARY_TARGET2 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 bitmasks to learn how to use these values to identify objects in this ancillary target program.
|Program (bit name)||Bit number||Target Description||Number of Fibers|
|HIZ_LRG||21||A candidate z > 0.6 LRG, selected using a narrower r-i color constraint and observed at higher priority||8,291|
|LRG_ROUND3||22||A candidate z > 0.6 LRG, selected using a broader r-i color constraint and observed at lower priority||2,543|
This ancillary science program used WISE and SDSS photometry to identify a sample of luminous red galaxies (LRGs) at redshift z > 0.6. The search for these galaxies takes advantage of the fact that old stellar populations show a local maximum in their spectral energy distributions at 1.6 µm (corresponding to a local minimum in the opacity of the H- ion) — and at z ~ 0.6, this “1.6 µm bump” is redshifted into the WISE W1 band.
The resulting sample can be used to calibrate photometric redshifts in this range, and to test target selection techniques for the SDSS’s upcoming eBOSS survey.
Targets for this program were divided into a higher priority sample indicated by the target flag
HIZ_LRG and a lower priority sample indicated by
LRG_ROUND3. For both samples, objects were required to have
(imodel < 20.0 || zmodel < 20.0) && (zfib2 < 21.7 || ifib2 < 22.0)
Objects in the
HIZ_LRG sample were selected to have
(r – i) > 0.98 && (r – W1) > 2(r – i) – 0.5
LRG_ROUND3 sample used the same r – W1 cut, but the (r – i) color cut was bluer, with (r – i) > 0.85, to explore a broader range of galaxy colors.