Faint End of the Quasar Luminosity Function


Photo of Nathalie Palanque-Delabrouille
Nathalie Palanque-Delabrouille
Institute of Research into the Fundamental Laws of the Universe
CEA Saclay


A survey of quasars designed to extend BOSS quasar selection to include fainter quasars

Finding Targets

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
QSO_DEEP 56 Candidate quasar selected by time variability 2,484
LBG 57 Candidate Lyman-break galaxy selected by color 168


Targets that have the QSO_DEEP bit set were designed to extend the selection of quasars to fainter objects, in particular for application to measurements of the quasar luminosity function.

Target Selection

Targets in this program have the same variability selection as those in the Variability-selected Quasars at 1 < z < 4 to g = 22.5 ancillary target program (target flag QSO_VAR_LF), but were selected in the range 22 < g < 23.5 from SDSS Stripe 82 data. Pointlike objects were selected to a neural network threshold of 0.5. Slightly extended objects with -0.15 < (rPSF – rmodel < +0.15 were selected to a neural network threshold of 0.9.

Additional targets were included in the sample when they had a large probability of being a quasar according to the Kernel Density Estimation (KDE; Richards et al. 2009). Unresolved objects with KDE(1.0 < z < 2.2) ≥ 0.999 or slightly-resolved objects with -0.05 < (rPSF – rmodel) &lt +0.05 and KDE(z > 2.2) ≥ 0.985 were included.

Targets previously spectroscopically identified as quasars were not included in the sample, and therefore do not have the QSO_DEEP target flag bit set even if they pass the selection criteria.

Finally, a sample of Lyman-Break Galaxies was selected in color-space and assigned the LBG target flag bit. These targets are slightly extended objects that lie in one of two color-box regions (joined by OR):

  • 0 < g – r < 0.15 AND (u – g) > (g – r) + 0.2
  • 0 < g – r < 1.0 AND (u – g) > (g – r) + 1.25


Richards, G. T., et al. 2009, ApJS, 180, 67