Galaxy populations in the Hydra I cluster from the VEGAS survey

I. Optical properties of a large sample of dwarf galaxies^⋆

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

Received: 29 July 2021
Accepted: 8 December 2021

Abstract

Context. Due to their relatively low stellar mass content and diffuse nature, the evolution of dwarf galaxies can be strongly affected by their environment. Analyzing the properties of the dwarf galaxies over a wide range of luminosities, sizes, morphological types, and environments, we can obtain insights about their evolution. At ∼50 Mpc, the Hydra I cluster of galaxies is among the closest cluster in the z ≃ 0 Universe, and an ideal environment to study dwarf galaxy properties in a cluster environment.

Aims. We exploit deep imaging data of the Hydra I cluster to construct a new photometric catalog of dwarf galaxies in the cluster core, which is then used to derive properties of the Hydra I cluster dwarf galaxy population as well as to compare it with other clusters. Moreover, we investigate the dependency of dwarf galaxy properties on their surrounding environment.

Methods. The new wide-field g- and r-band images of the Hydra I cluster obtained with the OmegaCAM camera on the VLT Survey Telescope (VST) in the context of the VST Early-type GAlaxy Survey (VEGAS) were used to study the dwarf galaxy population in the Hydra I cluster core down to r-band magnitude M_r = −11.5 mag. We used an automatic detection tool to identify dwarf galaxies from a ∼1 deg² field centered on the Hydra I core, covering almost half of the cluster virial radius. The photometric pipeline was used to estimate the principal photometric parameters for all targets. Scaling relations and visual inspection were used to assess the cluster membership and construct a new dwarf galaxy catalog. Finally, based on the new catalog, we studied the structural (Sérsic index n, effective radius R_e, and axis ratio) and photometric (colors and surface brightness) properties of the dwarf galaxies, also investigating how they vary as a function of clustercentric distance.

Results. The new Hydra I dwarf catalog contains 317 galaxies with a luminosity between −18.5 < M_r < −11.5 mag, a semi-major axis larger than ∼200 pc (a = 0.84″), of which 202 are new detections, and previously unknown dwarf galaxies in the Hydra I central region. We estimate that our detection efficiency reaches 50% at the limiting magnitude M_r = −11.5 mag, and at the mean effective surface brightness μ̄_e,r = 26.5 mag arcsec⁻². We present the standard scaling relations for dwarf galaxies, which are color-magnitude, size-luminosity, and Sérsic n-magnitude relations, and compare them with other nearby clusters. We find that there are no observational differences for dwarfs scaling relations in clusters of different sizes. We study the spatial distribution of galaxies, finding evidence for the presence of substructures within half the virial radius. We also find that mid- and high-luminosity dwarfs (M_r < −14.5 mag) become, on average, redder toward the cluster center, and that they have a mild increase in R_e with increasing clustercentric distance, similar to what is observed for the Fornax cluster. No clear clustercentric trends are reported for surface brightness and Sérsic index. Considering galaxies in the same magnitude bins, we find that for high and mid-luminosity dwarfs (M_r < −13.5 mag), the g − r color is redder for the brighter surface brightness and higher Sérsic n index objects. This finding is consistent with the effects of harassment and/or partial gas stripping.