Ultra-diffuse galaxies in the Kilo-Degree Survey with deep learning

Astronomy and Astrophysics, vol. 707, pp. A354

Abstract

Ultra-diffuse galaxies (UDGs) are a subset of low-surface-brightness galaxies (LSBGs), showing mean effective surface brightness fainter than 24 mag arcsec −2 and a diffuse morphology, with effective radii larger than 1.5 kpc. Due to their elusiveness, using traditional methods over large sky areas is challenging. Here we present a catalog of UDG candidates identified in the full 1350 deg 2 area of the Kilo-Degree Survey (KiDS) using deep learning. In particular, we used a previously developed network for the detection of low-surface-brightness systems in the Sloan Digital Sky Survey (SBGnet) and optimized for UDG detection. We trained this new UDG detection network for KiDS (UDGnet-K), with an iterative approach, starting from a small-scale training sample. After training and validation, the UGDnet-K has been able to identify ∼3300 UDG candidates, of which, after visual inspection, we selected 545 high-quality ones. The catalog contains the independent rediscovery of previously confirmed UDGs in local groups and clusters (e.g., NGC 5846 and Fornax), and new discovered candidates in about 15 local systems, for a total of 67 bona fide associations. Besides the value of the catalog per se for future studies of UDG properties, this work shows the effectiveness of an iterative approach to training deep learning tools in presence of poor training samples, due to the paucity of confirmed UDG examples, which we expect to replicate for upcoming all-sky surveys such as those by the Rubin Observatory, Euclid, and the China Space Station Telescope.

Authors 16

1. Hao Su

   Shandong University · University of Naples Federico II

   Affiliation as printed

   Department of Physics “E. Pancini”, University of Naples Federico II

   School of Mechanical, Electrical and Information Engineering, Shandong University

2. Rui Li

   Zhengzhou University · University of Chinese Academy of Sciences

   Affiliation as printed

   Institute for Astrophysics, School of Physics, Zhengzhou University

   School of Astronomy and Space Science, University of Chinese Academy of Sciences

3. Nicola R. Napolitano

   Istituto Nazionale di Fisica Nucleare · Astronomical Observatory of Capodimonte · Istituto Nazionale di Fisica Nucleare, Sezione di Napoli · University of Naples Federico II · National Institute for Astrophysics

   Affiliation as printed

   Department of Physics “E. Pancini”, University of Naples Federico II

   INAF – Osservatorio Astronomico di Capodimonte

   INFN, Sez. di Napoli

4. Zhenping Yi

   Shandong University

   Affiliation as printed

   School of Mechanical, Electrical and Information Engineering, Shandong University

5. C. Tortora

   Astronomical Observatory of Capodimonte · National Institute for Astrophysics

   Affiliation as printed

   INAF – Osservatorio Astronomico di Capodimonte

6. Yiping Su

   Shandong University

   Affiliation as printed

   School of Mechanical, Electrical and Information Engineering, Shandong University

7. Konrad H. Kuijken Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University

8. Liqing Chen

   Zhengzhou University

   Affiliation as printed

   Institute for Astrophysics, School of Physics, Zhengzhou University

9. Ran Li

   Zhengzhou University · University of Chinese Academy of Sciences

   Affiliation as printed

   Institute for Astrophysics, School of Physics, Zhengzhou University

   School of Astronomy and Space Science, University of Chinese Academy of Sciences

10. Rossella Ragusa

    Astronomical Observatory of Capodimonte · National Institute for Astrophysics

    Affiliation as printed

    INAF – Osservatorio Astronomico di Capodimonte

11. Sihan Li

    Zhengzhou University

    Affiliation as printed

    Institute for Astrophysics, School of Physics, Zhengzhou University

12. Yue Dong

    Xi’an Jiaotong-Liverpool University

    Affiliation as printed

    School of Mathematics and Physics, Xi’an Jiaotong-Liverpool University

13. M. Radovich

    Osservatorio Astronomico di Padova · National Institute for Astrophysics

    Affiliation as printed

    INAF – Osservatorio Astronomico di Padova

14. 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

15. G. Covone

    Istituto Nazionale di Fisica Nucleare · Astronomical Observatory of Capodimonte · Istituto Nazionale di Fisica Nucleare, Sezione di Napoli · University of Naples Federico II · National Institute for Astrophysics

    Affiliation as printed

    Department of Physics “E. Pancini”, University of Naples Federico II

    INAF – Osservatorio Astronomico di Capodimonte

    INFN, Sez. di Napoli

16. Fucheng Zhong

    Sun Yat-sen University · University of Naples Federico II

    Affiliation as printed

    Department of Physics “E. Pancini”, University of Naples Federico II

    School of Physics and Astronomy, Sun Yat-sen University, Zhuhai Campus