Enhancing photometric redshift catalogs through color-space analysis: Application to KiDS-bright galaxies

Astronomy and Astrophysics, vol. 692, pp. A177

Abstract

Aims. We present a method for refining photometric redshift galaxy catalogs based on a comparison of 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. Methods. Our approach uses a self-organizing map (SOM) to project a multidimensional parameter space of magnitudes and colors onto a 2D manifold, allowing us to analyze the resulting patterns as a function of various galaxy properties. Using SOM, we compared the Kilo-Degree Survey’s bright galaxy sample (KiDS-Bright), limited to r < 20 mag, with various spectroscopic samples, including the Galaxy And Mass Assembly (GAMA). Results. Our analysis reveals that GAMA tends to underrepresent KiDS-Bright at its faintest (r ≳ 19.5) and highest-redshift (z ≳ 0.4) ranges; however, no strong trends are seen in terms of color or stellar mass. By incorporating additional spectroscopic data from the SDSS, 2dF, and early DESI, we identified SOM cells where the photo-z values are estimated suboptimally. We derived 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, namely, it excludes the least represented 20% of the sample reduces photo-z scatter by less than 10%. Conclusions. 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 16

1. Priyanka Jalan

   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

2. Maciej Bilicki

   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

3. Wojciech A. Hellwing

   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

4. Angus H. Wright

   Ruhr University Bochum

   Affiliation as printed

   Ruhr University Bochum , Faculty of Physics and Astronomy , Astronomical Institute (AIRUB) , German Centre for Cosmological Lensing , 44780 Bochum , Germany

5. Andrej Dvornik

   Ruhr University Bochum

   Affiliation as printed

   Ruhr University Bochum , Faculty of Physics and Astronomy , Astronomical Institute (AIRUB) , German Centre for Cosmological Lensing , 44780 Bochum , Germany

6. Christos Georgiou

   Utrecht University

   Affiliation as printed

   Institute for Theoretical Physics , Utrecht University , Princetonplein 5 , 3584 CC Utrecht , The Netherlands

7. Catherine Heymans

   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

8. Hendrik Hildebrandt

   Ruhr University Bochum

   Affiliation as printed

   Ruhr University Bochum , Faculty of Physics and Astronomy , Astronomical Institute (AIRUB) , German Centre for Cosmological Lensing , 44780 Bochum , Germany

9. Shahab Joudaki

   Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas · University of Portsmouth

   Affiliation as printed

   Centro de Investigaciones Energéticas , Medioambientales y Tecnológicas (CIEMAT) , Av. Complutense 40 , E-28040 Madrid , Spain

   Institute of Cosmology & Gravitation , Dennis Sciama Building , University of Portsmouth , Portsmouth PO1 3FX , UK

10. Konrad H. Kuijken Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The Netherlands

11. Constance Mahony

    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

12. Szymon J. Nakoneczny

    California Institute of Technology

    Affiliation as printed

    Division of Physics, Mathematics and Astronomy , California Institute of Technology , 1200 E California Blvd , Pasadena , CA 91125 , USA

13. M. Radovich

    Osservatorio Astronomico di Padova

    Affiliation as printed

    INAF -Osservatorio Astronomico di Padova , Via dell'Osservatorio 5 , 35122 Padova , Italy

14. Jan Luca van den Busch

    Ruhr University Bochum

    Affiliation as printed

    Ruhr University Bochum , Faculty of Physics and Astronomy , Astronomical Institute (AIRUB) , German Centre for Cosmological Lensing , 44780 Bochum , Germany

15. Ziang Yan

    Ruhr University Bochum

    Affiliation as printed

    Ruhr University Bochum , Faculty of Physics and Astronomy , Astronomical Institute (AIRUB) , German Centre for Cosmological Lensing , 44780 Bochum , Germany

16. Mijin Yoon

    University of Portsmouth

    Affiliation as printed

    Institute of Cosmology & Gravitation , Dennis Sciama Building , University of Portsmouth , Portsmouth PO1 3FX , UK