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Description
We present accurate photometric redshifts (photo-z) in the 2-deg^2^ COSMOS field. The redshifts are computed with 30 broad, intermediate, and narrowbands covering the UV (Galaxy Evolution Explorer), visible near-IR (NIR; Subaru, Canada-France-Hawaii Telescope (CFHT), United Kingdom Infrared Telescope, and National Optical Astronomy Observatory), and mid-IR (Spitzer/IRAC). A {chi}^2^ template-fitting method (Le Phare) was used and calibrated with large spectroscopic samples from the Very Large Telescope Visible Multi-Object Spectrograph and the Keck Deep Extragalactic Imaging Multi-Object Spectrograph. We develop and implement a new method which accounts for the contributions from emission lines ([OII], 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=zs-zp) indicates a dispersion of {sigma}_{Delta}z/(1+zs)_=0.007 at i^+^_AB_<22.5, a factor of 2-6 times more accurate than earlier photo-z in the COSMOS, CFHT Legacy Survey, and the Classifying Object by Medium-Band Observations-17 survey fields. At fainter magnitudes i^+^_AB_<24 and z<1.25, the accuracy is {sigma}_{Delta}z/(1+zs)_=0.012. The deep NIR and Infrared Array Camera coverage enables the photo-z to be extended to z~2, albeit with a lower accuracy ({sigma}_{Delta}z/(1+zs)_=0.006 at i^+^_AB_~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 multiwavelength COSMOS catalog includes approximately 607,617 objects. The COSMOS-30 photo-z enables the full exploitation of this survey for studies of galaxy and large-scale structure evolution at high redshift.
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