We probe the atomic hydrogen (Hi) emission from the host galaxies of fast radio bursts (FRBs) to investigate the emerging trend of disturbance and asymmetry in the population. Quadrupling the sample size, we detect 16 out of 17 new hosts in Hi, with the single non-detection arising in a galaxy known to be transitioning towards quiescence. With respect to typical local Universe galaxies, FRB hosts are generally massive in Hi ( $\gt10^9$ M$_{{\odot}}$), which aligns with previous studies reporting that FRB hosts also tend to have high stellar masses and are star-forming. However, they span a broad range of other Hi derived properties. Using visual inspection alongside various asymmetry metrics, we identify six unambiguously settled host galaxies, demonstrating for the first time that a disturbed Hi morphology is not a universal feature of FRB host galaxies. However, we find another six that show clear signs of disturbance, one borderline case, and three which require deeper or more targeted observations to reach a conclusion; this brings the confirmed ratio of disturbed-to-settled FRB hosts to 11:6. Given that roughly a 1:1 ratio is expected for random background galaxies of similar type, our observed ratio yields a p-value of 0.222. Therefore, we conclude that contrary to earlier indications, there is no statistically significant excess of Hi disturbance in this sample of FRB host galaxies with respect to the general galaxy population, and hence we find no evidence for a fundamental connection between FRB progenitor formation and merger-induced star formation activity.

In this paper we present a wide-field radio survey at 300 MHz covering the sky from $-90^{\circ} \leq \delta_{\text{J2000}} \lesssim {+40}^{\circ}$ using the Murchison Widefield Array (MWA). This 300-MHz survey follows the Galactic and Extragalactic All-sky MWA (GLEAM) survey and provides an additional comparatively high-frequency data point to existing multi-frequency (72–231 MHz) data. With this data release we provide mosaic images and a catalogue of compact source components. We use two-minute snapshot observations covering 2015–2016, combining overlapping two-minute snapshot images to provide full-sensitivity mosaic images with a median root-mean-square noise of ${9.1_{-2.8}^{+5.5}}$ mJy beam$^{-1}$ and median angular resolution of ${128^{\prime\prime}8} \times {112^{\prime\prime}5}$, with some position-dependent variation. We find a total of 338 080 unique Gaussian components across the mosaic images. The survey is the first at 300 MHz from the MWA covering the whole Southern Hemisphere. It provides a unique spectral data point that complements the existing GLEAM survey and the ongoing GLEAM-eXtended survey and points towards results from the upcoming SKA-Low surveys.

Image reconstruction in very-long baseline interferometry operates under severely sparse aperture coverage with calibration challenges from both the participating instruments and propagation medium, which introduce the risk of biases and artefacts. Interferometric closure invariants offer calibration-independent information on the true source morphology, but the inverse transformation from closure invariants to the source intensity distribution is an ill-posed problem. In this work, we present a generative deep learning approach to tackle the inverse problem of directly reconstructing images from their observed closure invariants. Trained in a supervised manner with simple shapes and the CIFAR-10 dataset, the resulting trained model achieves reduced chi-square data adherence scores of $\chi^2_{\mathrm{CI}} \lesssim 1$ and maximum normalised cross-correlation image fidelity scores of $\rho_{\mathrm{NX}} \gt 0.9$ on tests of both trained and untrained morphologies, where $\rho_{\mathrm{NX}}=1$ denotes a perfect reconstruction. We also adapt our model for the Next Generation Event Horizon Telescope total intensity analysis challenge. Our results on quantitative metrics are competitive to other state-of-the-art image reconstruction algorithms. As an algorithm that does not require finely hand-tuned hyperparameters, this method offers a relatively simple and reproducible calibration-independent imaging solution for very-long baseline interferometry, which ultimately enhances the reliability of sparse very-long baseline radio interferometry imaging results.

Impulsive radio signals such as fast radio bursts (FRBs) are imprinted with the signatures of multi-path propagation through ionised media in the form of frequency-dependent temporal broadening of the pulse profile, commonly referred to as scattering. The dominant source of scattering for most FRBs is expected to be within their host galaxies, an assumption which can be tested by examining potential correlations between the scattering properties of the FRBs and global properties of their hosts. Using results from the Commensal Real-time ASKAP Fast Transient (CRAFT) survey, we investigate correlations across a range of host galaxy properties against attributes of the FRB that encode propagation effects: scattering timescale $\tau$, polarisation fractions, and absolute Faraday rotation measure. From 21 host galaxy properties considered, we find three that are correlated with $\tau$, including the stellar surface density (or compactness; Pearson’s p-value p = 0.002 and Spearman’s p = 0.010), the mass-weighted age (Spearman’s p-value p = 0.009), and a weaker correlation with the gas-phase metallicity (Spearman’s $p = 0.017$). Weakly significant correlations are also found with $H\alpha$ equivalent widths and stellar gravitational potential. From 10 000 trials of reshuffled datasets, we expect two strong Spearman’s correlations only 2% of the time and three weaker correlations in 6.6% of cases. Compact host galaxies may have more ionised content which scatters the FRB further. Compact galaxies were also found to correlate with gas-phase metallicity in our sample, while H ii regions along the line-of-sight are also a potential contributing factor. No correlation is seen with host galaxy inclination, which weakens the case for an inclination bias, as previously suggested for samples of localised FRBs. A strong ($p = 0.002$) correlation is found for absolute rotation measure with optical disc axis ratio b/a; greater rotation measures are seen for edge-on host galaxies. Further high-time resolution FRB detections, coupled with localisation and detailed follow-up on their host galaxies, are necessary to corroborate these initial findings and shed further light into the FRB mechanism.

The impact of galaxy cluster mergers on the properties of the resident galaxies remains poorly understood. In this paper, we investigate the effects of merging environments on star formation (SF) activity in nearby clusters ($0.04\lt z\lt0.06$) from the SAMI Galaxy Survey – A168, A2399, A3880, and EDCC 0442 – which exhibit different dynamical activity. Using single-fibre spectroscopy from the SAMI Cluster Redshift Survey and Sloan Digital Sky Survey, we trace SF activity across the cluster sample by identifying the star-forming galaxy (SFG) population based on spectral features. We find a mild enhancement in the star-forming galaxy fraction ($f_{SFG}$) in merging clusters, although not statistically significant. The spatial and projected phase-space distributions show that SFGs in merging clusters are well-mixed with the passive population, while galaxy populations exhibit a clear segregation in the relaxed clusters. Analysis of the equivalent width of the H$\alpha$ line, as a tracer of recent SF activity, does not reveal strong evidence of triggered SF activity as a function of dynamical state for both the global cluster environment and subsamples of galaxies selected near possible merger features. This suggests that the increase in $f_{SFG}$ is due to the mixing of galaxies in dynamically complex, young merging systems that are still forming, unlike their older, relaxed counterparts that have had longer to quench.

Observational evidence regarding the impact of Active Galactic Nucleu (AGN) feedback on star formation (SF) in non-jetted galaxies is limited. With the available high-resolution UV observations from AstroSat-UVIT, complemented by GALEX, we studied the SF properties in the outskirts ($\gt0.5R_{25}$) of six AGN-host galaxies and compared them with four non-AGN galaxies of similar morphology. We observed a higher SF rate density ($\Sigma_{\text{SFR}}$) for the UV knots in AGN-host galaxies, and it falls off less rapidly compared to non-AGN galaxies, suggesting positive AGN feedback in the outskirts of AGN-host galaxies. Additionally, FUV attenuation (A$_{\text{FUV}}$) is also enhanced in the outer regions and falls less rapidly in AGN-host compared to non-AGN, indicating that the feedback could be coupled with dust. We speculate that the radiation-pressure-driven and/or wind mode AGN feedback could be at play even in low-luminosity nearby AGN-host galaxies.

We review the state of the evidence for the existence and observational appearance of supermassive black hole binaries. Such objects are expected from standard hierarchical galaxy evolution to form after two galaxies, each containing a supermassive black hole, have merged, in the centre of the merger remnant. A complex interaction is predicted to take place with stars and gas in the host galaxy, leading to observable signatures in weakly as well as actively accreting phases. Direct observational evidence is available and shows examples of dual active galactic nuclei from kpc scales down to parsec scales. Signatures of possibly closer supermassive black hole binaries may be seen in jetted black holes. The interaction with stars and gas in a galaxy significantly affects the hardening of the binary and hence contributes to uncertainties of the expected gravitational wave signal. The Laser Interferometer Space Antenna (LISA) should in the future detect actual mergers. Before the launch of LISA, pulsar timing arrays may have the best chance to detect a gravitational wave signal from supermassive black hole binaries. The first signs of the combined background of inspiralling objects might have been seen already.

The lowest mass at which the third dredge-up (TDU) occurs for thermally pulsing asymptotic giant branch (TP-AGB) stars remains a key uncertainty in detailed stellar models. S-type AGB stars are an important constraint on this uncertainty as they have C/O ratios between 0.5 and 1, meaning they have only experienced up to a few episodes of TDU. AGB stars are also long-period variable stars, pulsating in low order radial pulsation modes. In this paper, we estimate the initial masses of a large sample of intrinsic S-type AGB stars, by analysing their visual light curves, estimating their luminosities with Gaia DR3 parallax distances and finally comparing to a grid of detailed stellar models combined with linear pulsation models. We find that the initial mass distribution of intrinsic S-type stars peaks at 1.3–1.4 M$_{\odot}$ depending on model assumptions. There also appear to be stars with initial masses down to 1 solar mass, which is in conflict with current detailed stellar models. Additionally, we find that though the mass estimates for semiregular variable stars pulsating in higher order radial modes are precise, the Mira variables pulsating in the fundamental mode present challenges observationally from uncertain parallax distances, and theoretically from the onset of increased mass-loss and the necessity of non-linear pulsation models.

This work explores the morphology and dynamical properties of cores within rich superclusters, highlighting their role as transitional structures in the large-scale structure of the Universe. Using projected and radial velocity distributions of member galaxies, we identify cores as dense structures that, despite being gravitationally bound, are not yet dynamically relaxed. However, they exhibit a tendency towards virialisation, evolving in a self-similar manner to massive galaxy clusters but on a larger scale. Morphological analysis reveals that cores are predominantly filamentary, reflecting quasi-linear formation processes consistent with the Zeldovich approximation. Our estimates of the entropy confirm their intermediate dynamical state, with relaxation levels varying across the sample. Mass estimates indicate efficient accretion processes, concentrating matter into gravitationally bound systems. We conclude that cores are important environments where galaxy evolution and hierarchical assembly occur, bridging the gap between supercluster-scale structures and virialised clusters.

We present a comprehensive spectro-temporal analysis of GRS $1915+105$ observed with AstroSat during June, 2017. A detailed study of the temporal properties reveals the appearance of an ‘unknown’ variability class ($\tau$) during $\unicode{x03C1} \rightarrow \unicode{x03BA}$ class transition of the source. This new ‘unknown’ class ($\tau$) is characterised by the irregular repetition of low count ‘dips’ along with the adjacent ‘flare’ like features in between two successive steady count rate durations, resulting in uniform ‘C’ shaped distribution in the colour-colour diagram. A detailed comparative study of the variability properties between the $\tau$ class and other known variability classes of GRS $1915+105$ indicates it as a distinct variability class of the source. Further, we find evidence of the presence of possible HFQPO features at ${\sim} 71$ Hz with quality factor ${\sim} 13$, rms amplitude ${\sim} 4.69\%$, and significance $3\sigma$, respectively. In addition, a harmonic-like feature at ${\sim} 152$ Hz is also seen with quality factor ${\sim} 21$, rms amplitude ${\sim} 5.75\%$, and significance ${\sim} 4.7\sigma$. The energy-dependent power spectral study reveals that the fundamental HFQPO and its harmonic are present in 3–15 keV and 3–6 keV energy ranges, respectively. Moreover, the wide-band (0.7–50 keV) spectral modelling comprising of thermal Comptonization component indicates the presence of a cool ($kT_\textrm{e}\sim 1.7$ keV) and optically thick (optical depth ${\sim} 14$) Comptonizing ‘corona’, which seems to be responsible in regulating the HFQPO features in GRS 1915+105. Finally, we find the bolometric luminosity ($L_\textrm{bol}$) to be about $42\% L_\textrm{Edd}$ within 1–100 keV, indicating the sub-Eddington accretion regime of the source.

The 6.7 GHz methanol maser transition is exclusively associated with young, high-mass stars and represents a potential target for astrometric studies, including accurate determination of their distance through trigonometric parallax measurements. There are more than 1 000 known 6.7 GHz methanol maser sources in the Milky Way; however, not all are suitable targets for astrometric measurements. We have used the Long Baseline Array to observe 187 southern 6.7 GHz methanol masers and identify 69 sources with one or more maser spots that are sufficiently compact and intense to be suitable targets for very long baseline interferometry astrometry with current instruments. Maser compactness appears to be a strong function of Galactic position, with masers that are likely in nearby spiral arms being more compact, while those associated with distant arms or the central Galactic region being less compact – a relationship we associate with scatter broadening. This has implications for astrophysical masers, especially distant ones employed for Galactic astrometry.

High-redshift protoclusters are crucial for understanding the formation of galaxy clusters and the evolution of galaxies in dense environments. The James Webb Space Telescope (JWST), with its unprecedented near-infrared sensitivity, enables the first exploration of protoclusters beyond $ z \gt 10 $. Among JWST surveys, COSMOS-Web Data Release 0.5 offers the largest area ($\sim 0.27$ deg$^2$), making it an optimal field for protocluster searches. In this study, we searched for protoclusters at $ z \sim 9-10 $ using 366 F115W dropout galaxies. We evaluated the reliability of our photometric redshift by validation tests with the JADES DR3 spectroscopic sample, obtaining the likelihood of falsely identifying interlopers as $\sim25\%$. Overdensities ($\delta$) are computed by weighting galaxy positions with their photometric redshift probability density functions, using a 2.5 cMpc aperture and a redshift slice of $\pm 0.5$. We selected the most promising core galaxies of protocluster candidate galaxies with an overdensity greater than the 95th percentile of the distribution of 366 F115W dropout galaxies. The member galaxies are then linked within an angular separation of 7.5 cMpc to the core galaxies, finding seven protocluster candidates. These seven protocluster candidates have inferred halo masses of $ M_{\text{halo}} \sim 10^{11}\,{\rm M}_{\odot} $. The detection of such overdensities at these redshifts provides a critical test for current cosmological simulations. However, confirming these candidates and distinguishing them from low-redshift dusty star-forming galaxies or Balmer-break galaxies will require follow-up near-infrared spectroscopic observations.

We present the third data release for the Galactic and Extragalactic All-Sky Murchison Widefield Array eXtended (GLEAM-X) survey, covering $\approx 3\,800$ deg$^2$ of the southern Galactic Plane (GP) with ${233}^{\circ} \lt l \lt {44}^{\circ}$ and $|b| \lt {11}^{\circ}$ across a frequency range of 72–231 MHz divided into 20 sub-bands. GLEAM-X observations were taken using the ‘extended’ Phase-ii configuration of the Murchison Widefield Array (MWA), which features baselines ranging from approximately 12 m to 5 km. This configuration limits sensitivity to the diffuse structure of the GP, with an angular resolution range of about $45^{''}$ to $2^{'}$. To achieve lower noise levels while being sensitive to a wide range of spatial scales ($45^{''} - {15}^{\circ}$), we combined these observations with the previous Galactic and Extragalactic All-Sky Murchison Widefield Array (GLEAM) survey. For the area covered, we provide images spanning the whole frequency range. A wide-band image over 170–231 MHz, with RMS noise of $\approx\;$3–6 mJy beam$^{-1}$ and source position accuracy within 1 arcsec, is then used to perform source-finding, which yields 98 207 elements measured across $20 \times 7.68$ MHz frequency bands. The catalogue is 90$\%$ complete at 50 mJy within ${233}^{\circ} \lt l \lt {324}^{\circ}$ and at 125 mJy in ${290}^{\circ} \lt l \lt {44}^{\circ}$, while it is $99.3\%$ reliable overall. All the images and the catalogue are available online for download.

Radio galaxy remnants are a rare subset of the radio-loud active galactic nuclei (RLAGN) population, representing the quiescent phase in the RLAGN lifecycle. Despite their observed scarcity, they offer valuable insights into the AGN duty cycle and feedback processes. Due to the mega-year timescales over which the RLAGN lifecycle takes place, it is impossible to observe the active to remnant transition in real-time. Numerical simulations offer a solution to follow the long-term evolution of RLAGN plasma. In this work, we present the largest suite (to date) of three-dimensional, hydrodynamic simulations studying the dynamic evolution of the active-to-remnant transition and explore the mechanisms driving cocoon evolution, comparing the results to the expectations of analytic modelling. Our results show key differences between active and remnant sources in both cluster environments and in lower-density group environments. We find that sources in low-density environments can remain overpressured well into the remnant phase. This significantly increases the time for the remnant lobe to transition to a buoyant regime. We compare our results with analytic expectations, showing that the long-term evolution of radio remnants can be well captured for remnants whose expansion is largely pressure-driven if the transition to a coasting phase is assumed to be gradual. We find that remnants of low-powered progenitors can continue to be momentum-driven for about 10 Myr after the jets switch-off. Finally, we consider how the properties of the progenitor influence the mixing of the remnant lobe and confirm the expectation that the remnants of high-powered sources have long-lasting shocks that can continue to heat the surrounding medium.

Post-asymptotic giant branch (Post-AGB) and post-red giant branch (post-RGB) binaries with stable circumbinary discs provide key insights into late stellar and disc evolution, revealing how binary interactions shape disc structure and stellar surface composition. A defining trait of such systems is the observed underabundance of refractory elements in the stellar photosphere relative to volatile elements – photospheric chemical depletion – resulting from the star accreting volatile-rich circumstellar gas. In this study, we investigated the link between photospheric depletion and disc evolution by focusing on post-AGB/post-RGB binaries with low infrared excess (hereafter ‘faint disc’ targets). We analysed high-resolution optical spectra from HERMES/Mercator and UVES/VLT for 6 Galactic and 2 LMC targets. Using E-iSpec, we homogeneously derived atmospheric parameters and chemical abundances of 29 elements from carbon to europium, and included NLTE corrections for 15 elements from carbon to barium that we calculated using pySME and pre-computed grids of departure coefficients. All targets exhibit ‘saturated’ depletion patterns, which we characterised using two-piece linear fits defined by three parameters: initial metallicity ([M/H]$_0$), turn-off temperature ($T_\textrm{turn-off}$), and depletion scale ($\nabla_\textrm{ 100 K}$). Among several findings, we highlight the bimodal distribution of $T_\textrm{turn-off}$ in faint disc targets, which allows classification into two subgroups analogous to full discs with continuous, optically thick dust ($T_\textrm{turn-off} \gt 1 100$ K), and transition discs with inner clearing ($T_\textrm{turn-off} \lt 1 100$ K). Our results imply that faint disc targets likely represent the final stages of disc dissipation, highlighting the diversity of depletion profiles, the complexity of disc-binary interactions, and the need to understand the rarity and evolution of faint disc systems.

Several radio telescopes have been planned or proposed to be deployed on the Lunar farside in the coming years. These will observe the unexplored ultra-long wavelengths of the electromagnetic spectrum from the lunar farside’s unique radio-quiet and ionosphere-free environment. One such lunar radio array is the NASA-funded concept – the Farside Array for Radio Science Investigations of the Dark Ages and Exoplanets (FARSIDE). FARSIDE will operate over 100 kHz to 40 MHz with 128 spatially non-co-located orthogonal pairs of antenna nodes distributed over a $12\times12$ km area in a four-arm spiral configuration. Being on the lunar farside, this radio interferometer will be deployed by tele-operated rovers. The rover deployment mode could lead to a phase offset between each of the two orthogonally polarised antenna elements in the array, which are typically co-located. In this paper, we quantify the effects of such antenna phase offsets on the polarisation response and imaging performance of the lunar radio array. Modelling and analysing the FARSIDE dipole beams with and without offset, we find the latter leads to additional leakages into Stokes U and V corresponding to Muller matrix terms of $M_{2(0,1,2,3)}$ and $M_{3(0,1,2,3)}$. Using a custom simulation pipeline to incorporate all four Stokes beams of spatially co-located and non-co-located dipoles, we produce visibilities and simulated images for the GLEAM (GaLactic and Extragalactic All-sky MWA) sky model through the FARSIDE array. We find that for a pure Stokes I input sky, the output image maximum Stokes $V/I$ flux ratio for the offset case has increased to $2.5\%$ versus $0.05\%$ for the co-located case. The additional Stokes V needs to be corrected since the detection of electron cyclotron maser emissions from exoplanets requires high-fidelity Stokes V measurements.

We investigate the effect of turbulent magnetic fields on the observed spectral properties of synchrotron radio emission in large-scale radio galaxy lobes. We use three-dimensional relativistic magnetohydrodynamic simulations of fast, high-powered jets to study the structure of the lobe magnetic fields and how this structure affects the radio spectrum of the lobes. It has previously been argued that lobe ages inferred from radio spectra underestimate the true ages of radio galaxies due to re-acceleration of electrons in the lobe, mixing of electron populations, or the presence of turbulent magnetic fields in the lobes. We find that the spectral ages with and without accounting for the lobe magnetic field structure are consistent with each other, suggesting that mixing of radiating populations of different ages is the primary cause of the underestimation of radio lobe ages. By accounting for the structure of lobe magnetic fields, we find greater spectral steepening in the equatorial regions of the lobe. We demonstrate that the assumptions of the continuous injection, Jaffe–Perola, and Tribble models for radio lobe spectra do not hold in our simulations, and we show that young particles with high magnetic field strengths are the dominant contributors to the overall radio lobe spectrum.

This paper reports the discovery and follow-up of four candidate redback spider pulsars: GPM J1723$-33$, GPM J1734$-28$, GPM J1752$-30$, and GPM J1815$-14$, discovered with the Murchison Widefield Array (MWA) from an imaging survey of the Galactic Plane. These sources are considered to be redback candidates based on their eclipsing variability, steep negative spectral indices, and potential Fermi $\gamma$-ray associations, with GPM J1723$-33$ and GPM J1815$-14$ lying within a Fermi 95$\%$ error ellipse. Follow-up pulsation searches with MeerKAT confirmed pulsations from GPM J1723$-33$, while the non-detections of the other three are likely due to scattering by material ablated from their companion stars. We identify possible orbital periods by applying folding algorithms to the light curves and determine that all sources have short orbital periods ($\lt$24 h), consistent with redback spider systems. Following up on the sources at multiple radio frequencies revealed that the sources exhibit frequency-dependent eclipses, with longer eclipses observed at lower frequencies. We place broad constraints on the eclipse medium, ruling out induced Compton scattering and cyclotron absorption. Three sources are spatially consistent with optical sources in the Dark Energy Camera Plane Survey imaging, which may contain the optical counterparts. Each field is affected by strong dust extinction, and follow-up with large telescopes is needed to identify the true counterparts. Identifying potential radio counterparts to four previously unassociated Fermi sources brings us closer to understanding the origin of the unexplained $\gamma$-ray excess in the Galactic Centre.

We present a new method to calculate the polarised synchrotron emission of radio Active Galactic Nuclei (AGN) sources using magnetic field information from 3-dimensional relativistic magnetohydrodynamical (RMHD) simulations. Like its predecessor, which uses pressure as a proxy for the magnetic field, this method tracks the spatially resolved adiabatic and radiative loss processes using the method adapted from the Radio AGN in Semi-analytic Environments formalism. Lagrangian tracer particles in RMHD simulations carried out using the PLUTO code are used to track the fluid quantities of each ‘ensemble of electrons’ through time to calculate the radio emissivity ex situ. By using the magnetic field directly from simulations, the full set of linear Stokes parameters I, Q, and U can be calculated to study the synthetic radio polarisation of radio AGN sources. We apply this method to a suite of RMHD simulations to study their polarisation properties. The turbulent magnetic field present in radio lobes influences the emission, causing a complex clumpy structure that is visible at high resolution. Our synthetic polarisation properties are consistent with observations; we find that the fractional polarisation is highest (approximately 50%) at the lobe edges. We show that for the same source, the integrated and mean fractional polarisation depends on viewing angle to the source. At oblique viewing angles the behaviour of the integrated and mean fractional polarisation over time depends on the morphology of the jet cocoon. Using Faraday rotation measures, we reproduce known depolarisation effects such as the Laing-Garrington depolarisation asymmetry in jets angled to the line of sight. We show that the hotspots and hence the Fanaroff–Riley classification become less clear with our new, more accurate method.