Enhancing Photometric Redshift Catalogs Through Color-Space Analysis: Application to KiDS-Bright Galaxies
Abstract
We present a method to refine photometric redshift galaxy catalogs by comparing their color-space matching with overlapping spectroscopic calibration data. We focus on cases where photometric redshifts (photo-$z$) are estimated empirically. Identifying galaxies that are poorly represented in spectroscopic data is crucial, as their photo-$z$ may be unreliable due to extrapolation beyond the training sample. Our approach uses a self-organizing map (SOM) to project a multi-dimensional parameter space of magnitudes and colors onto a 2-D manifold, allowing us to analyze the resulting patterns as a function of various galaxy properties. Using SOM, we compare the Kilo-Degree Survey bright galaxy sample (KiDS-Bright), limited to $r<20$ mag, with various spectroscopic samples, including the Galaxy And Mass Assembly (GAMA). Our analysis reveals that GAMA under-represents KiDS-Bright at its faintest ($r\gtrsim19.5$) and highest-redshift ($z\gtrsim0.4$) ranges, however no strong trends in color or stellar mass. By incorporating additional spectroscopic data from the SDSS, 2dF, and early DESI, we identify SOM cells where photo-$z$ are estimated suboptimally. We derive a set of SOM-based criteria to refine the photometric sample and improve photo-$z$ statistics. For the KiDS-Bright sample, this improvement is modest: exclusion of the least represented 20% of the sample reduces photo-$z$ scatter by less than 10%. We conclude that GAMA, used for KiDS-Bright photo-$z$ training, is sufficiently representative for reliable redshift estimation across most of the color space. Future spectroscopic data from surveys such as DESI should be better suited for exploiting the full improvement potential of our method.
Authors 14
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Center for Theoretical Physics · Polish Academy of Sciences
Affiliation as printed
Center for Theoretical Physics , Polish Academy of Sciences , Al. Lotników 32/46 , 02-668 , Warsaw , Poland
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Center for Theoretical Physics · Polish Academy of Sciences
Affiliation as printed
Center for Theoretical Physics , Polish Academy of Sciences , Al. Lotników 32/46 , 02-668 , Warsaw , Poland
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Center for Theoretical Physics · Polish Academy of Sciences
Affiliation as printed
Center for Theoretical Physics , Polish Academy of Sciences , Al. Lotników 32/46 , 02-668 , Warsaw , Poland
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Affiliation as printed
Ruhr University Bochum , Faculty of Physics and Astronomy , Astronomical Institute (AIRUB) , German Centre for Cosmological Lensing , 44780 Bochum , Germany
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Affiliation as printed
Ruhr University Bochum , Faculty of Physics and Astronomy , Astronomical Institute (AIRUB) , German Centre for Cosmological Lensing , 44780 Bochum , Germany
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Royal Observatory · Ruhr University Bochum · University of Edinburgh
Affiliation as printed
Institute for Astronomy , University of Edinburgh , Royal Observatory , Blackford Hill , Edinburgh , EH9 3HJ , UK
Ruhr University Bochum , Faculty of Physics and Astronomy , Astronomical Institute (AIRUB) , German Centre for Cosmological Lensing , 44780 Bochum , Germany
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Affiliation as printed
Ruhr University Bochum , Faculty of Physics and Astronomy , Astronomical Institute (AIRUB) , German Centre for Cosmological Lensing , 44780 Bochum , Germany
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Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas · University of Portsmouth
Affiliation as printed
Centro de Investigaciones Energé ticas , Medioambientales y Tecnoló gicas (CIEMAT) , Av. Complutense 40 , E-28040 Madrid , Spain
Institute of Cosmology & Gravitation , Dennis Sciama Building , University of Portsmouth , Portsmouth , PO1 3FX , UK
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , the Netherlands
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Donostia International Physics Center · Ruhr University Bochum
Affiliation as printed
Donostia International Physics Center , Manuel Lardizabal Ibilbidea , 4 , 20018 Donostia , Gipuzkoa , Spain
Ruhr University Bochum , Faculty of Physics and Astronomy , Astronomical Institute (AIRUB) , German Centre for Cosmological Lensing , 44780 Bochum , Germany
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California Institute of Technology
Affiliation as printed
Division of Physics, Mathematics and Astronomy , California Institute of Technology , 1200 E California Blvd , Pasadena , CA 91125
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Osservatorio Astronomico di Padova · National Institute for Astrophysics
Affiliation as printed
INAF -Osservatorio Astronomico di Padova , via dell'Osservatorio 5 , 35122 Padova , Italy
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Affiliation as printed
Institute of Cosmology & Gravitation , Dennis Sciama Building , University of Portsmouth , Portsmouth , PO1 3FX , UK
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