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We present the largest low frequency (120~MHz) arcminute resolution image of the radio synchrotron background (RSB) to date, and its corresponding angular power spectrum of anisotropies (APS) with angular scales ranging from $3^\circ$ to $0.3^\prime$. We show that the RSB around the North Celestial Pole has a significant excess anisotropy power at all scales over a model of unclustered point sources based on source counts of known source classes. This anisotropy excess, which does not seem attributable to the diffuse Galactic emission, could be linked to the surface brightness excess of the RSB. To better understand the information contained within the measured APS, we model the RSB varying the brightness distribution, size, and angular clustering of potential sources. We show that the observed APS could be produced by a population of faint clustered point sources only if the clustering is extreme and the size of the Gaussian clusters is $\lesssim 1'$. We also show that the observed APS could be produced by a population of faint diffuse sources with sizes $\lesssim 1'$, and this is supported by features present in our image. Both of these cases would also cause an associated surface brightness excess. These classes of sources are in a parameter space not well probed by even the deepest radio surveys to date., Comment: 13 pages, 14 figures. Accepted for publication in MNRAS

Fast radio bursts (FRBs) are extragalactic radio transients of extraordinary luminosity. Studying the diverse temporal and spectral behaviour recently observed in a number of FRBs may help determine the nature of the entire class. For example, a fast spinning or highly magnetised neutron star might generate the rotation-powered acceleration required to explain the bright emission. Periodic, sub-second components, suggesting such rotation, were recently reported in one FRB, and potentially in two more. Here we report the discovery of FRB 20201020A with Apertif, an FRB showing five components regularly spaced by 0.415 ms. This sub-millisecond structure in FRB 20201020A carries important clues about the progenitor of this FRB specifically, and potentially about that of FRBs in general. We thus contrast its features to the predictions of the main FRB source models. We perform a timing analysis of the FRB 20201020A components to determine the significance of the periodicity. We compare these against the timing properties of the previously reported CHIME FRBs with sub-second quasi-periodic components, and against two Apertif bursts from repeating FRB 20180916B that show complex time-frequency structure. We find the periodicity of FRB 20201020A to be marginally significant at 2.5$\sigma$. Its repeating subcomponents cannot be explained as a pulsar rotation since the required spin rate of over 2 kHz exceeds the limits set by typical neutron star equations of state and observations. The fast periodicity is also in conflict with a compact object merger scenario. These quasi-periodic components could, however, be caused by equidistant emitting regions in the magnetosphere of a magnetar. The sub-millisecond spacing of the components in FRB 20201020A, the smallest observed so far in a one-off FRB, may rule out both neutron-star rotation and binary mergers as the direct source of quasi-periodic FRBs., Comment: 13 pages, 6 figures, 3 tables, supplementary material. Submitted to A&A

We describe the APERture Tile In Focus (Apertif) system, a phased array feed (PAF) upgrade of the Westerbork Synthesis Radio Telescope which has transformed this telescope into a high-sensitivity, wide field-of-view L-band imaging and transient survey instrument. Using novel PAF technology, up to 40 partially overlapping beams can be formed on the sky simultaneously, significantly increasing the survey speed of the telescope. With this upgraded instrument, an imaging survey covering an area of 2300 deg2 is being performed which will deliver both continuum and spectral line data sets, of which the first data has been publicly released. In addition, a time domain transient and pulsar survey covering 15,000 deg2 is in progress. An overview of the Apertif science drivers, hardware and software of the upgraded telescope is presented, along with its key performance characteristics., 29 pages, 42 figures, accepted for publication by A&A

We report on the results from deep HI observations, performed with the Karoo Array Telescope and with the Karl G. Jansky Very Large Array of the loose galaxy group centred on the early-type galaxy IC 1459. The main result from our observations is the detection of a nearly continuous, 500-kpc long HI tail which crosses the entire group. Earlier observations with the Australia Telescope Compact Array had shown the presence of a large HI tail in this galaxy group, but because of the much larger coverage of the new data, the full extent of this tail is now visible. The HI mass of this structure is 3.1 +- 0.3 10^9 Msun . Based on its morphology and kinematics, we conclude that the tail consists of gas stripped from NGC 7418 through tidal interactions, with ram-pressure affects playing at most a minor role. Optical images of the IC 1459 group do not show many indications that galaxy interactions are common in this group. The HI data reveal a very different picture and show that almost all gas-rich galaxies in the IC 1459 group have a distorted HI distribution indicating that many interactions are occurring in this group. This high number of interactions shows that the processes that drive galaxy transformation are also occurring in fairly loose galaxy groups., 4 pages. Submitted to Astronomy and Astrophysics Letters

Context. Pisces A and Pisces B are the only two galaxies found via optical imaging and spectroscopy out of 22 HI clouds identified in the GALFAHI survey as dwarf galaxy candidates. Aims: We derive the HI content and kinematics of Pisces A and B. Methods. Our aperture synthesis H observations used the seven-dish Karoo Array Telescope (KAT-7), which is a pathfinder instrument for MeerKAT, the South African precursor to the mid-frequency Square Kilometre Array (SKA-MID). Results: The low rotation velocities of ∼5 km s−1 and ∼10 km s−1 in Pisces A and B, respectively, and their HI content show that they are really dwarf irregular galaxies (dIrr). Despite that small rotation component, it is more the random motions ∼9−11 km s−1 that provide most of the gravitational support, especially in the outer parts. The study of their kinematics, especially the strong gradients of random motions, suggest that those two dwarf galaxies are not yet in equilibrium. Conclusions. These HI- rich galaxies may be indicative of a large population of dwarfs at the limit of detectability. However, such gasrich dwarf galaxies will most likely never be within the virial radius of MW-type galaxies and become subhalo candidates. Systems such as Pisces A and B are more likely to be found at a few Mpc s from MW-type galaxies.

We present HI observations of the Sculptor Group starburst spiral galaxy NGC 253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for the SKA precursor MeerKAT, under construction. The short baselines and low system temperature of the telescope make it very sensitive to large scale, low surface brightness emission. The KAT-7 observations detected 33% more flux than previous VLA observations, mainly in the outer parts and in the halo for a total HI mass of $2.1 \pm 0.1$ $\times 10^{9}$ M$_{\odot}$. HI can be found at large distances perpendicular to the plane out to projected distances of ~9-10 kpc away from the nucleus and ~13-14 kpc at the edge of the disk. A novel technique, based on interactive profile fitting, was used to separate the main disk gas from the anomalous (halo) gas. The rotation curve (RC) derived for the HI disk confirms that it is declining in the outer parts, as seen in previous optical Fabry-Perot measurements. As for the anomalous component, its RC has a very shallow gradient in the inner parts and turns over at the same radius as the disk, kinematically lagging by ~100 km/sec. The kinematics of the observed extra planar gas is compatible with an outflow due to the central starburst and galactic fountains in the outer parts. However, the gas kinematics shows no evidence for inflow. Analysis of the near-IR WISE data, shows clearly that the star formation rate (SFR) is compatible with the starburst nature of NGC 253., Comment: 18 pages, 20 figures, 8 Tables. Accepted for publication to MNRAS

Many early-type galaxies are detected at 24 to 160 micron but the emission is usually dominated by an AGN or heating from the evolved stellar population. Here we present MIPS observations of a sample of elliptical and lenticular galaxies which are rich in cold molecular gas, and we investigate how much of the MIR to FIR emission could be due to star formation activity. The 24 micron images show a rich variety of structures, including nuclear point sources, rings, disks, and smooth extended emission, and comparisons to matched-resolution CO and radio continuum images suggest that the bulk of the 24 micron emission can be traced to star formation. The star formation efficiencies are comparable to those found in normal spirals. Some future directions for progress are also mentioned., Comment: 9 pages, 3 color figures. This is a contributed paper to the conference "The Evolving ISM in the Milky Way and Nearby Galaxies," the 4th Spitzer Science Center Conference (Pasadena, December 2007). It also appears on the conference web pages

Supermassive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei is crucial for understanding the impact of the energy they release on the host galaxy. For radio AGN, this can be done by identifying dying (remnant) and restarted radio galaxies from their radio spectral properties. Using the combination of images at 1400 MHz produced by Apertif, the new phased-array feed receiver installed on the Westerbork Synthesis Radio Telescope, and images at 150 MHz provided by LOFAR, we have derived resolved spectral index images (at a resolution of ~15 arcsec) for all the sources within ~6 deg^2 area of the Lockman Hole region. We were able to select 15 extended radio sources with emission (partly or entirely) characterised by extremely steep spectral indices (steeper than 1.2). These objects represent radio sources in the remnant or the restarted phases of their life cycle. Our findings suggest this cycle to be relatively fast. They also show a variety of properties relevant for modelling the evolution of radio galaxies. For example, the restarted activity can occur while the remnant structure from a previous phase of activity is still visible. This provides constraints on the duration of the 'off' (dying) phase. In extended remnants with ultra-steep spectra at low frequencies, the activity likely stopped a few hundred megayears ago, and they correspond to the older tail of the age distribution of radio galaxies, in agreement with simulations of radio source evolution. We find remnant radio sources with a variety of structures (from double-lobed to amorphous), suggesting different types of progenitors. The present work sets the stage for exploiting low-frequency spectral index studies of extended sources by taking advantage of the large areas common to the LOFAR and the Apertif surveys., Accepted for publication in A&A. This paper is part of the 1st data release of the LoTSS Deep Fields. 17 pages, 10 figures