Cosmos Photometric Redshifts with 30-Bands for 2-deg2
Kneib, J. -P.; Aussel, H.; Le Floc'h, E.; Sanders, D. B.; Ilbert, O.; Murayama, T.; Taniguchi, Y.; Salvato, M.; Bolzonella, M.; Brusa, M.; Tanaka, M.; Silverman, J.; Hasinger, G.; Mainieri, V.; Capak, P.; Arnouts, S.; Surace, J.; Carollo, C. M.; Lilly, S.; McCracken, H. J.; Scoville, N.; Mignoli, M.; Zamorani, G.; Tasca, L.; Le Fèvre, O.; Kartaltepe, J.; Thompson, D.; Mobasher, B.; Peng, Y.; Garilli, B.; Bardelli, S.; Zucca, E.; Cucciati, O.; Scodeggio, M.; Leauthaud, A.; Bongiorno, A.; Schiminovich, D.; Pérez-Montero, E.; Caputi, K. I.; Renzini, A.; Zamojski, M.; Contini, T.; Tresse, L.; Mellier, Y.; Kampczyk, P.; Coppa, G.; de la Torre, S.; de Ravel, L.; Franzetti, P.; Iovino, A.; Knobel, C.; Lamareille, F.; Le Brun, V.; Maier, C.; Ricciardelli, E.; Vergani, D.; Shioya, Y.; Cook, R.; Sasaki, S.; Kovac, K.; Le Borgne, J. F.; Pellò, R.; Looper, D.
United States, France, Japan, Germany, Italy, Switzerland
Abstract
We present accurate photometric redshifts (photo-z) in the 2-deg2 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 χ2 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 ([O II], Hβ, Hα, and Lyα) 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., Δz = z s - z p) indicates a dispersion of σ_{Δ 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, 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 σ_{Δ z/(1+z_s)}=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 (σ_{Δ z/(1+z_s)}=0.06 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.