We present accurate photometric redshifts in the 2-deg ^ { 2 } COSMOS field .
The redshifts are computed with 30 broad , intermediate , and narrow bands covering the UV ( GALEX ) , Visible-NIR ( Subaru , CFHT , UKIRT and NOAO ) and mid-IR ( Spitzer /IRAC ) .
A \chi ^ { 2 } template-fitting method ( Le Phare ) was used and calibrated with large spectroscopic samples from VLT-VIMOS and Keck-DEIMOS .
We develop and implement a new method which accounts for the contributions from emission lines ( [ O ii ] , H \beta , H \alpha and Ly \alpha ) to the spectral energy distributions ( SEDs ) .
The treatment of emission lines improves the photo-z accuracy by a factor of 2.5 .
Comparison of the derived photo-z with 4148 spectroscopic redshifts ( i.e . \Delta z = z _ { s } - z _ { p } ) indicates a dispersion of \sigma _ { \Delta z / ( 1 + z _ { s } ) } = 0.007 at i ^ { + } _ { AB } < 22.5 , a factor of 2 - 6 times more accurate than earlier photo-z in the COSMOS , CFHTLS and COMBO-17 survey fields .
At fainter magnitudes i ^ { + } _ { AB } < 24 and z < 1.25 , the accuracy is \sigma _ { \Delta z / ( 1 + z _ { s } ) } = 0.012 .
The deep NIR and IRAC coverage enables the photo-z to be extended to z \sim 2 albeit with a lower accuracy ( \sigma _ { \Delta z / ( 1 + z _ { s } ) } = 0.06 at i ^ { + } _ { AB } \sim 24 ) .
The redshift distribution of large magnitude-selected samples is derived and the median redshift is found to range from z _ { m } = 0.66 at 22 < i ^ { + } _ { AB } < 22.5 to z _ { m } = 1.06 at 24.5 < i ^ { + } _ { AB } < 25 .
At i ^ { + } _ { AB } < 26.0 , the multi-wavelength COSMOS catalog includes approximately 607,617 objects .
The COSMOS-30 photo-z enable the full exploitation of this survey for studies of galaxy and large scale structure evolution at high redshift .