COSMOS PHOTOMETRIC REDSHIFTS WITH 30-BANDS FOR 2-deg²

Abstract

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 χ 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], 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. ∆z = z s − z p ) indicates a dispersion of σ ∆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, CFHTLS and COMBO-17 survey fields. At fainter magnitudes i + AB < 24 and z < 1.25, the accuracy is σ ∆z/(1+zs) = 0.012. The deep NIR and IRAC coverage enables the photo-z to be extended to z ∼ 2 albeit with a lower accuracy (σ ∆z/(1+zs) = 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 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.

Comparing Dark Energy Survey andHST–CLASH observations of the galaxy cluster RXC J2248.7−4431: implications for stellar mass versus dark matter

“…We run LEPHARE on both CLASH (with five, eight and all 17 filters) and DES (five filters) catalogues, fitting the 31 synthetic SEDs templates given by the COSMOS (see Ilbert et al 2009) libraries. We use four galaxy extinction values ranging from 0.05 to 0.3 using a Calzetti et al (2000) extinction law for DES.…”

Dusty star-forming galaxies at high redshift

“…as in the COSMOS field; Scoville et al, 2007) has made photometric redshifts increasingly reliable (e.g. Ilbert et al, 2009) and much less observationally expensive than obtaining spectroscopic redshifts. Spectroscopic redshifts for faint (i ∼ 23 − 25) galaxies might require a few hours of integration on an >8 m class telescope.…”

A cooperative approach among methods for photometric redshifts estimation: an application to KiDS data

“…As reference template set we adopted the 31 SED models used for COSMOS photo-z's (Ilbert et al 2009) (see Fig. 1).…”

“…However, we followed the setup discussed in Ilbert et al (2009), i.e. we did not apply any galactic extinction correction for models redder than the Sc templates; the galactic extinction curve provided by Prevot et al (1984) is used for templates redder than SB3 model, while Calzetti et al (2000) is adopted for those bluer (including SB3 template).…”

“…we did not apply any galactic extinction correction for models redder than the Sc templates; the galactic extinction curve provided by Prevot et al (1984) is used for templates redder than SB3 model, while Calzetti et al (2000) is adopted for those bluer (including SB3 template). Emission lines added to the templates were also implemented as discussed in Ilbert et al (2009). Finally, Le PHARE also provides an adaptive procedure, which calculates the shifts in the photometric zero-points.…”