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We present MeerKAT Fornax Survey H I observations of NGC 1427A, a blue irregular galaxy with a stellar mass of ∼2 × 109 M⊙ located near the centre of the Fornax galaxy cluster. Thanks to the excellent resolution (1–6 kpc spatially, 1.4 km s−1 in velocity) and H I column density sensitivity (∼4 × 1019 to ∼1018 cm−2 depending on resolution), our data deliver new insights on the long-debated interaction of this galaxy with the cluster environment. We confirm the presence of a broad, one-sided, starless H I tail stretching from the outer regions of the stellar body and pointing away from the cluster centre. We find the tail to have 50% more H I (4 × 108 M⊙) and to be 3 times longer (70 kpc) than in previous observations. In fact, we detect scattered H I clouds out to 300 kpc from the galaxy in the direction of the tail – possibly the most ancient remnant of the passage of NGC 1427A through the intracluster medium of Fornax. Both the velocity gradient along the H I tail and the peculiar kinematics of H I in the outer region of the stellar body are consistent with the effect of ram pressure given the line-of-sight motion of the galaxy within the cluster. However, several properties cannot be explained solely by ram pressure and suggest an ongoing tidal interaction. This includes: the close match between dense H I and stars within the disturbed stellar body; the abundant kinematically anomalous H I; and the inversion of the H I velocity gradient near the base of the H I tail. We rule out an interaction with the cluster tidal field, and conclude that NGC 1427A is the result of a high-speed galaxy encounter or of a merger started at least 300 Myr ago, where ram pressure shapes the distribution and kinematics of the H I in the perturbed outer stellar body and in the tidal tails. [ABSTRACT FROM AUTHOR]

We present the results of a Very Large Array H i imaging survey aimed at understanding why some galaxies develop long extraplanar H α tails, becoming extreme jellyfish galaxies. The observations are centered on five extreme jellyfish galaxies optically selected from the WINGS and OMEGAWINGS surveys and confirmed to have long H α tails through MUSE observations. Each galaxy is located in a different cluster. In the observations, there are in total 88 other spiral galaxies within the field of view (40′ Ă— 40′) and observed bandwidth (6500 km sâˆ'1). We detect 13 of these 88 spirals, plus one uncataloged spiral, with H i masses ranging from 1 to 7 Ă— 109 M ⊙. Many of these detections have extended H i disks, two show direct evidence for ram pressure stripping, and others are possibly affected by tidal forces and/or ram pressure stripping. We stack the 75 nondetected spiral galaxies and find an average H i mass of 1.9 Ă— 108 M ⊙, which, given their average stellar mass, implies that they are very H i deficient. Comparing the extreme jellyfish galaxies to the other disk galaxies, we find that they are at smaller projected distance from the cluster center, and have a higher stellar mass and higher relative velocity than all other H i detections and most nondetections. We conclude that the high stellar mass allows extreme jellyfish galaxies to fall deeply into the cluster before being stripped, and the surrounding ICM pressure gives rise to their spectacular star-forming tails. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present VLA H  i observations of JO206, a prototypical ram-pressure-stripped galaxy in the GASP sample. This massive galaxy (M * = 8.5 × 1010 M⊙) is located at a redshift of z  = 0.0513, near the centre of the low-mass galaxy cluster, IIZw108 (σ ∼ 575  km s−1). JO206 is characterized by a long tail (≥90 kpc) of ionized gas stripped away by ram pressure. We find a similarly long H  i tail in the same direction as the ionized gas tail and measure a total H  i mass of 3.2 × 109 M⊙. This is about half the expected H  i mass given the stellar mass and surface density of JO206. A total of 1.8 × 109 M⊙ (60 per cent) of the detected H  i is in the gas-stripped tail. An analysis of the star formation rate shows that the galaxy is forming more stars compared to galaxies with the same stellar and H  i mass. On average we find an H  i gas depletion time of ∼0.5 Gyr which is about four times shorter than that of 'normal' spiral galaxies. We performed a spatially resolved analysis of the relation between star formation rate density and gas density in the disc and tail of the galaxy at the resolution of our H  i data. The star formation efficiency of the disc is about 10 times higher than that of the tail at fixed H  i surface densities. Both the inner and outer parts of JO206 show an enhanced star formation compared to regions of similar H  i surface density in field galaxies. The enhanced star formation is due to ram-pressure stripping during the galaxy's first infall into the cluster. [ABSTRACT FROM AUTHOR]