We present — and make publicly available — accurate and precise photometric redshifts in the ACS footprint from the COSMOS field for objects with iAB<23. The redshifts are computed using a combination of narrow band photometry from PAUS, a survey with 40 narrow bands spaced at 100Å intervals covering the range from 4500Å to 8500Å, and 26 broad, intermediate, and narrow bands covering the UV, visible and near infrared spectrum from the COSMOS2015 catalogue. We introduce a new method that models the spectral energy distributions (SEDs) as a linear combination of continuum and emission line templates and computes its Bayes evidence, integrating over the linear combinations. The correlation between the UV luminosity and the OII line is measured using the 66 available bands with the zCOSMOS spectroscopic sample, and used as a prior which constrains the relative flux between continuum and emission line templates. The flux ratios between the OII line and Hα, Hβ and OIII are similarly measured and used to generate the emission line templates. Comparing to public spectroscopic surveys via the quantity Δz≡(zphoto−zspec)/(1+zspec), we find the photometric redshifts to be more precise than previous estimates, with σ68(Δz)≈(0.003,0.009) for galaxies at magnitude iAB∼18 and iAB∼23, respectively, which is 3× and 1.66× tighter than COSMOS2015. Additionally, we find the redshifts to be very accurate on average, yielding a median of the Δz distribution compatible with |median(Δz)|≤0.001 at all redshifts and magnitudes considered. Both the added PAUS data and new methodology contribute significantly to the improved results.
For extensive details see Alarcon et al. 2020.
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Some summary details:
- The catalog includes galaxies with magnitude I-AUTO < 23 in the COSMOS field.
- The photometric redshift is measured using the 40 narrow bands from PAUS, and a combination of narrow, intermediate and broad bands from different instruments from the COSMOS survey.
- The photometric redshift is run between redshift 0 and 3, in steps of 0.001 between redshift 0 and 1, in steps of 0.002 between redshift 1 and 1.5, and in steps of 0.01 between redshift 1.5 and 3.0.
- The photometric redshift is defined as the mode of the redshift distribution of each galaxy.
- The full redshift distribution is provided, at the redshifts values where the code is run.
- The flux line (and error) of the OII, OIII, Hbeta and Halpha lines is measured for each object at the photometric redshift using the best model. The measurements are corrected for internal galaxy dust extinction.
- The absolute magnitudes of the GALEX NUV, CFHT u, Subaru r and i bands are measured using the photometric redshift of the catalog and the best model. The measurements are corrected for internal galaxy dust extinction.
- The best model, extinction law and extinction value is given for each object.