A near-infrared study of the obscured 3C129 galaxy cluster^⋆

¹ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 Groningen, AV, The Netherlands
² Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
³ Department of Physics and Electronics, Rhodes University, PO Box 94, Makhanda 6140, South Africa
e-mail: m.ramatsoku@ru.ac.za
⁴ South African Astronomical Observatory (SAAO), PO Box 9, 7935 Observatory, Cape Town, South Africa
⁵ School of Mathematics and Physics, University of Queensland, Brisbane, QLD 4072, Australia

Received: 4 May 2020
Accepted: 31 August 2020

Abstract

We present a catalogue of 261 new infrared selected members of the 3C 129 galaxy cluster. The cluster, located at z ≈ 0.02, forms part of the Perseus-Pisces filament and is obscured at optical wavelengths due to its location in the zone of avoidance. We identified these galaxies using the J- and K-band imaging data provided by the UKIDSS Galactic Plane Survey within an area with a radius of 1.1° centred on the X-ray emission of the cluster at ℓ, b ≈ 160.52° ,0.27°. A total of 26 of the identified galaxy members have known redshifts 24 of which are from our 2016 Westerbork H I survey and two are from optical spectroscopy. An analysis of the galaxy density at the core of the 3C 129 cluster shows it to be less dense than the Coma and Norma clusters, but comparable to the galaxy density in the core of the Perseus cluster. From an assessment of the spatial and velocity distributions of the 3C 129 cluster galaxies that have redshifts, we derived a velocity of cz = 5227 ± 171 km s⁻¹ and σ = 1097 ± 252 km s⁻¹ for the main cluster, with a substructure in the cluster outskirts at cz = 6923 ± 71 km s⁻¹ with σ = 422 ± 100 km s⁻¹. The presence of this substructure is consistent with previous claims based on the X-ray analysis that the cluster is not yet virialised and may have undergone a recent merger.