General description: The xdcore files contain quasar probabilities in three redshift ranges derived using the XDQSO technique, as described in Bovy et al. (2011). The quasar probabilities are assigned based on models for the underlying flux distributions of quasars and stars applied to the single-epoch ugriz fluxes of all 160,904,060 point-sources with dereddened i-band magnitude between 17.75 and 22.45 mag in DR8.
Naming convention: Filenames have the form xdcore_RUN6.fits.
File type: FITS
| HDU0 | NULL | Empty |
| HDU1 fields | Binary FITS Table | Quasar probabilities |
Note: Additional HDUs may be present for engineering purposes, but are not supported and are subject to change. Users should refrain from using HDUs not listed here.
HDU 1 contains quasar probabilities based on single-epoch SDSS ugriz data as described in the binary table documented below.
OBJID Unique SDSS identifier composed from [skyVersion,rerun,run,camcol,field,obj].
RUN SDSS imaging run number
RERUN SDSS processing rerun number
CAMCOL Camera column
FIELD Field number
ID The object ID within a field
RA Right ascension in decimal degrees (J2000.0)
DEC Declination in decimal degrees (J2000.0)
PHOTOMETRIC Indicates whether this object was observed under good imaging conditions (True/False)
PSFMAG[5] PSF Uebercalibrated ugriz asinh magnitude (corrected for Galactic extinction)
PSFMAGERR[5] Error in PSF ugriz asinh magnitude
EXTINCTION_U Extinction in u band; A_u/A_g/A_r/A_i/A_z= 5.155/3.793/2.751/2.086/1.479
QSOLOWZLIKE Relative-flux density factor p({f_j/f_i} | f_i,z < 2.2 quasar)
QSOMIDZLIKE Same as previous, but for 2.2 ≤ z ≤ 3.5 quasar
QSOHIZLIKE Same as previous, but for z > 3.5 quasar
STARLIKE Same as previous, but for star
QSOLOWZNUMBER Number density as a function of apparent magnitude for this object for the z < 2.2 quasar class
QSOMIDZNUMBER Same as previous, but for 2.2 ≤ z ≤ 3.5 quasar
QSOHIZNUMBER Same as previous, but for z > 3.5 quasar
STARNUMBER Same as previous, but for star
PQSOLOWZ Probability that the object is a z < 2.2 quasar
PQSOMIDZ Probability that the object is a 2.2 ≤ z ≤ 3.5 quasar
PQSOHIZ Probability that the object is a z > 3.5 quasar
PQSO Probability that the object is a quasar (sum of previous three)
PSTAR Probability that the object is a star
BITMASK BOSS quasar target selection bitmask (see Sheldon et al., 2011, in preparation; appendix A of Bovy et al. 2011)
GOOD good flag: 0: passes all BOSS cuts, 1: fails basic BOSS cut (see paper), 2: fails other BOSS cuts (see Bovy et al. 2011).