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We present MeerKAT Fornax Survey H Iobservations of NGC 1427A, a blue irregular galaxy with a stellar mass of ∼2 × 10⁹M_⊙located near the centre of the Fornax galaxy cluster. Thanks to the excellent resolution (1–6 kpc spatially, 1.4 km s⁻¹in velocity) and H Icolumn density sensitivity (∼4 × 10¹⁹to ∼10¹⁸cm⁻²depending 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 Itail 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 × 10⁸M_⊙) and to be 3 times longer (70 kpc) than in previous observations. In fact, we detect scattered H Iclouds 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 Itail and the peculiar kinematics of H Iin 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 Iand stars within the disturbed stellar body; the abundant kinematically anomalous H I; and the inversion of the H Ivelocity gradient near the base of the H Itail. 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 Iin the perturbed outer stellar body and in the tidal tails. 

The MeerKAT Fornax Survey maps the distribution and kinematics of atomic neutral hydrogen gas (H  I ) in the nearby Fornax galaxy cluster using the MeerKAT telescope. The 12 deg 2 survey footprint covers the central region of the cluster out to ∼ R vir and stretches south-west out to ∼2 R vir to include the NGC 1316 galaxy group. The H  I column density sensitivity (3 σ over 25 km s −1 ) ranges from 5 × 10 19 cm −2 at a resolution of ∼10″ (∼1 kpc at the 20 Mpc distance of Fornax) down to ∼10 18 cm −2 at ∼1′ (∼6 kpc), and slightly below this level at the lowest resolution of ∼100″ (∼10 kpc). The H  I mass sensitivity (3 σ over 50 km s −1 ) is 6 × 10 5 M ⊙ . The H  I velocity resolution is 1.4 km s −1 . In this paper, we describe the survey design and H  I data processing, and we present a sample of six galaxies with long, one-sided, starless H  I tails (only one of which was previously known) radially oriented within the cluster and with measurable internal velocity gradients. We argue that the joint properties of the H  I tails represent the first unambiguous evidence of ram pressure shaping the distribution of H  I in the Fornax cluster. The disturbed optical morphology of all host galaxies supports the idea that the tails consist of H  I that was initially pulled out of the galaxies’ stellar body by tidal forces. Ram pressure was then able to further displace the weakly bound H  I and give the tails their current direction, length, and velocity gradient. 

Abstract We present the full panchromatic afterglow light-curve data of GW170817, including new radio data as well as archival optical and X-ray data, between 0.5 and 940 days post-merger. By compiling all archival data and reprocessing a subset of it, we have evaluated the impact of differences in data processing or flux determination methods used by different groups and attempted to mitigate these differences to provide a more uniform data set. Simple power-law fits to the uniform afterglow light curve indicate a t 0.86±0.04 rise, a t −1.92±0.12 decline, and a peak occurring at 155 ± 4 days. The afterglow is optically thin throughout its evolution, consistent with a single spectral index (−0.584 ± 0.002) across all epochs. This gives a precise and updated estimate of the electron power-law index, p = 2.168 ± 0.004. By studying the diffuse X-ray emission from the host galaxy, we place a conservative upper limit on the hot ionized interstellar medium density, <0.01 cm −3 , consistent with previous afterglow studies. Using the late-time afterglow data we rule out any long-lived neutron star remnant having a magnetic field strength between 10 10.4 and 10 16 G. Our fits to the afterglow data using an analytical model that includes Very Long Baseline Interferometry proper motion from Mooley et al., and a structured jet model that ignores the proper motion, indicates that the proper-motion measurement needs to be considered when seeking an accurate estimate of the viewing angle. 

Aims. We present the results of three commissioning H  I observations obtained with the MeerKAT radio telescope. These observations make up part of the preparation for the forthcoming MHONGOOSE nearby galaxy survey, which is a MeerKAT large survey project that will study the accretion of gas in galaxies and the link between gas and star formation. Methods. We used the available H  I data sets, along with ancillary data at other wavelengths, to study the morphology of the MHONGOOSE sample galaxy, ESO 302-G014, which is a nearby gas-rich dwarf galaxy. Results. We find that ESO 302-G014 has a lopsided, asymmetric outer disc with a low column density. In addition, we find a tail or filament of H  I clouds extending away from the galaxy, as well as an isolated H  I cloud some 20 kpc to the south of the galaxy. We suggest that these features indicate a minor interaction with a low-mass galaxy. Optical imaging shows a possible dwarf galaxy near the tail, but based on the current data, we cannot confirm any association with ESO 302-G014. Nonetheless, an interaction scenario with some kind of low-mass companion is still supported by the presence of a significant amount of molecular gas, which is almost equal to the stellar mass, and a number of prominent stellar clusters, which suggest recently triggered star formation. Conclusions. These data show that MeerKAT produces exquisite imaging data. The forthcoming full-depth survey observations of ESO 302-G014 and other sample galaxies will, therefore, offer insights into the fate of neutral gas as it moves from the intergalactic medium onto galaxies.