Galaxy populations in the Hydra I cluster from the VEGAS survey

II. The ultra-diffuse galaxy population

¹ INAF – Astronomical Observatory of Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
e-mail: antoniolamarca46@gmail.com
² Kapteyn Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
³ University of Naples “Federico II”, C.U. Monte Sant’Angelo, Via Cinthia, 80126 Naples, Italy
⁴ INAF – Astronomical Observatory of Abruzzo, Via Maggini, 64100 Teramo, Italy
⁵ Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
⁶ European Southern Observatory, Karl–Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁷ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁸ INAF – Astronomical Observatory of Padova, Via dell’Osservatorio 8, 36012 Asiago, (VI), Italy
⁹ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
¹⁰ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
¹¹ Space Physics and Astronomy Research Unit, University of Oulu, PO Box 3000 90014 Oulu, Finland
¹² Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
¹³ INAF – Astronomical Observatory of Rome, Via Frascati, 33, 00078 Monte Porzio Catone, Rome, Italy

Received: 4 October 2021
Accepted: 13 June 2022

Abstract

In this work, we extend the catalog of low-surface brightness (LSB) galaxies, including ultra-diffuse galaxy (UDG) candidates, within ≈0.4R_vir of the Hydra I cluster of galaxies based on deep images from the VST Early-type GAlaxy Survey (VEGAS). The new galaxies were found by applying an automatic detection tool and carrying out additional visual inspections of g and r band images. This led to the detection of 11 UDGs and 8 more LSB galaxies. For all of them, we assessed the cluster membership using the color–magnitude relation derived for early-type giant and dwarf galaxies in Hydra I. The UDGs and new LSB galaxies found in Hydra I span a wide range of central surface brightness (22.7 ≲ μ_0, g ≲ 26.5 mag arcsec⁻²), effective radius (0.6 ≲ R_e ≲ 4.0 kpc), and color (0.4 ≤ g − r ≤ 0.9 mag), and have stellar masses in the range ∼5 × 10⁶ − 2 × 10⁸ M_⊙. The 2D projected distribution of both galaxy types is similar to the spatial distribution of dwarf galaxies, with over-densities in the cluster core and north of the cluster center. They have similar color distribution and comparable stellar masses to the red dwarf galaxies. Based on photometric selection, we identify a total of nine globular cluster (GC) candidates associated to the UDGs and four to the LSB galaxies, with the highest number of candidates in an individual UDG being three. We find that there are no relevant differences between dwarfs, LSB galaxies, and UDGs: the structural parameters (i.e., surface brightness, size, color, and n-index) and GC content of the three classes have similar properties and trends. This finding is consistent with UDGs being the extreme LSB tail of the size–luminosity distribution of dwarfs in this environment.