We describe the automated spectral classification , redshift determination , and parameter measurement pipeline in use for the Baryon Oscillation Spectroscopic Survey ( BOSS ) of the Sloan Digital Sky Survey III ( SDSS-III ) as of the survey ’ s Ninth Data Release ( DR9 ) , encompassing 831,000 moderate-resolution optical spectra .
We give a review of the algorithms employed , and describe the changes to the pipeline that have been implemented for BOSS relative to previous SDSS-I/II versions , including new sets of stellar , galaxy , and quasar redshift templates .
For the color-selected “ CMASS ” sample of massive galaxies at redshift 0.4 \lesssim z \lesssim 0.8 targeted by BOSS for the purposes of large-scale cosmological measurements , the pipeline achieves an automated classification success rate of 98.7 % and confirms 95.4 % of unique CMASS targets as galaxies ( with the balance being mostly M stars ) .
Based on visual inspections of a subset of BOSS galaxies , we find that approximately 0.2 % of confidently reported CMASS sample classifications and redshifts are incorrect , and about 0.4 % of all CMASS spectra are objects unclassified by the current algorithm which are potentially recoverable .
The BOSS pipeline confirms that \sim 51.5 % of the quasar targets have quasar spectra , with the balance mainly consisting of stars and low signal-to-noise spectra .
Statistical ( as opposed to systematic ) redshift errors propagated from photon noise are typically a few tens of km s ^ { -1 } for both galaxies and quasars , with a significant tail to a few hundreds of km s ^ { -1 } for quasars .
We test the accuracy of these statistical redshift error estimates using repeat observations , finding them underestimated by a factor of 1.19 to 1.34 for galaxies , and by a factor of 2 for quasars .
We assess the impact of sky-subtraction quality , signal-to-noise ratio , and other factors on galaxy redshift success .
Finally , we document known issues with the BOSS DR9 spectroscopic data set , and describe directions of ongoing development .