We present the discovery of nine quasars at z \sim 6 identified in the Sloan Digital Sky Survey ( SDSS ) imaging data .
This completes our survey of z \sim 6 quasars in the SDSS footprint .
Our final sample consists of 52 quasars at 5.7 < z \leq 6.4 , including 29 quasars with z _ { AB } \leq 20 mag selected from 11,240 deg ^ { 2 } of the SDSS single-epoch imaging survey ( the main survey ) , 10 quasars with 20 \leq z _ { AB } \leq 20.5 selected from 4223 deg ^ { 2 } of the SDSS overlap regions ( regions with two or more imaging scans ) , and 13 quasars down to z _ { AB } \approx 22 mag from the 277 deg ^ { 2 } in Stripe 82 .
They span a wide luminosity range of -29.0 \leq M _ { 1450 } \leq - 24.5 .
This well-defined sample is used to derive the quasar luminosity function ( QLF ) at z \sim 6 .
After combining our SDSS sample with two faint ( M _ { 1450 } \geq - 23 mag ) quasars from the literature , we obtain the parameters for a double power-law fit to the QLF .
The bright-end slope \beta of the QLF is well constrained to be \beta = -2.8 \pm 0.2 .
Due to the small number of low-luminosity quasars , the faint-end slope \alpha and the characteristic magnitude M _ { 1450 } ^ { \ast } are less well constrained , with \alpha = -1.90 _ { -0.44 } ^ { +0.58 } and M ^ { \ast } = -25.2 _ { -3.8 } ^ { +1.2 } mag .
The spatial density of luminous quasars , parametrized as \rho ( M _ { 1450 } < -26 ,z ) = \rho ( z = 6 ) 10 ^ { k ( z - 6 ) } , drops rapidly from z \sim 5 to 6 , with k = -0.72 \pm 0.11 .
Based on our fitted QLF and assuming an IGM clumping factor of C = 3 , we find that the observed quasar population can not provide enough photons to ionize the z \sim 6 IGM at \sim 90 % confidence .
Quasars may still provide a significant fraction of the required photons , although much larger samples of faint quasars are needed for more stringent constraints on the quasar contribution to reionization .