In order to study the structure and temperature distribution within high-mass star-forming clumps, we employed the Australia Telescope Compact Array to image the $\mathrm{NH}_3$ (J,K) = (1,1) through (6,6) and the (2,1) inversion transitions, the $\mathrm{H}_2\mathrm{O}$ $6_{16}$-$5_{23}$ maser line at 22.23508 GHz, several $\mathrm{CH}_3\mathrm{OH}$ lines and hydrogen and helium recombination lines. In addition, 22- and 24-GHz radio continuum emission was also imaged.

The $\mathrm{NH}_3$ lines probe the optical depth and gas temperature of compact structures within the clumps. The $\mathrm{H}_2\mathrm{O}$ maser pinpoints the location of shocked gas associated with star formation. The recombination lines and the continuum emission trace the ionised gas associated with hot OB stars. The paper describes the data and presents sample images and spectra towards select clumps. The technique for estimating gas temperature from $\mathrm{NH}_3$ line ratios is described. The data show widespread hyperfine intensity anomalies in the $\mathrm{NH}_3$ (1,1) images, an indicator of non-LTE $\mathrm{NH}_3$ excitation. We also identify several new $\mathrm{NH}_3$ (3,3) masers associated with shocked gas. Towards AGAL328.809+00.632, the $\mathrm{H}_2\mathrm{O}$ $6_{16}$-$5_{23}$ line, normally seen as a maser, is instead seen as a thermally excited absorption feature against a strong background continuum. The data products are described in detail.

Simulations suggest that slow rotating galaxies are the result of galaxy-galaxy mergers that have a tendency to randomise stellar orbits. The exact pathway for slow rotator formation, however, is still unclear. Our aim is to see whether there is a relationship between fossil groups - whose central galaxies are thought to have undergone more major merging than other central galaxies – and the stellar kinematic properties of those central galaxies. We classify all galaxy groups in the GAMA redshift survey whose central galaxies were observed with SAMI as: (i) fossil groups, (ii) mass gap groups (fossil-like groups), and (iii) groups that are not dynamically evolved (NDEGs, i.e. controls). We compare the following properties of centrals across the three different group types: spin ($\lambda_{Re}$), the fraction of slow rotators ($f_{SR}$), and age. We also repeat our analysis on data from the EAGLE and Magneticum hydrodynamical cosmological simulations. In SAMI, we find that the spin parameter, slow rotator fraction, and age are broadly consistent across our three group types, i.e. the fossil groups, mass gap groups and NDEGs. We do find a weak indication that $f_{SR}$ is slightly lower for fossil group centrals as compared to NDEG centrals. In contrast, in EAGLE and Magneticum, fossil and mass gap group centrals typically have a significantly lower $\lambda_{Re}$ than NDEG centrals. Our results for SAMI suggest that the types of mergers that form fossil groups are not the types of mergers that form slow rotators. Merger count may be less important for slow rotator formation than specific merger conditions, such as the gas content of progenitors. When and where the merging occurs are also suspected to play an important role in slow rotator formation, and these conditions may differ for fossil group formation.

We conducted a study on the X-ray polarisation properties of MCG-5-23-16 by analysing long-term monitoring data from NuSTAR jointly with IXPE observations made in May and November 2022. The re-analysis of IXPE data gives model-dependent polarisation degree, PD (%) = $1.08\pm0.66$ in the energy band 2–8 keV, which agrees with previous studies within error bars. The model-independent analysis of PD poses an upper limit of $\leq3.8$ ($1\sigma$ level) for the same energy band. The observed upper limit of PD, along with broadband spectral analysis (2–79 keV) using an accretion-ejection based model, allowed us to derive the corona geometry (i.e. radius and height) and the accretion disc inclination ($\sim33^\circ$). Additional NuSTAR observations were also analysed to gain insights into the accretion flow properties of the source and to estimate the expected polarisation during those epochs with PD $\sim 4.3\%$. The radius and height of the corona varies between $28.2\pm3.1 - 39.8\pm4.6$ r$_s$ and $14.3\pm1.7-21.4\pm1.9$ r$_s$ respectively, with a mass outflow rate from the corona measuring $0.14\pm0.03-0.2\pm0.03$ Eddington rate ($\dot m_{\mathrm{Edd}}$). The estimated PD values were nearly constant up to a certain radial distance and height of the corona and then decreased for increasing corona geometry. The spectral analysis further provided an estimate for the mass of the central black hole $\sim2\times 10^7$ M$_\odot$ and the velocity of the outflowing gas $\sim0.16-0.19c$. A comparative broadband spectral study using reflection-based models estimates the disc inclination between $\sim 31^\circ\pm8^\circ-45^\circ\pm7^\circ$, and yields an expected PD of 3.4–6.0%. We also found a weak reflection fraction and a less ionised distant reflecting medium. The expected PD measured using accretion-ejection and reflection models is less compared to the expected PD measured for a given disc inclination of $45^\circ$. Our modelling of the disc-corona-outflows and polarisation connection can be extended and validated with data from the recently launched XPoSat, India’s first X-ray Polarimeter Satellite, offering potential applications to other sources.

The angular correlation is a method for measuring the distribution of structure in the Universe, through the statistical properties of the angular distribution of galaxies on the sky. We measure the angular correlation of galaxies from the second data release of the GaLactic and Extragalactic All-sky Murchison Widefield Array eXtended survey (GLEAM-X) survey, a low-frequency radio survey covering declinations below $+30^\circ$. We find an angular distribution consistent with the $\Lambda$CDM cosmological model assuming the best fitting cosmological parameters from Planck Collaboration et al. (2020, A&A, 641, A6). We fit a bias function to the discrete tracers of the underlying matter distribution, finding a bias that evolves with redshift in either a linear or exponential fashion to be a better fit to the data than a constant bias. We perform a covariance analysis to obtain an estimation of the properties of the errors, by analytic, jackknife, and sample variance means. Our results are consistent with previous studies on the topic, and also the predictions of the $\Lambda$CDM cosmological model.

We present deep near-infrared $K_\textrm{s}$-band imaging for 35 of the 53 sources from the high-redshift ($z \gt 2$) radio galaxy candidate sample defined in Broderick et al. (2022, PASA, 39, e061). These images were obtained using the High-Acuity Widefield K-band Imager (HAWK-I) on the Very Large Telescope. Host galaxies are detected for 27 of the sources, with $K_\textrm{s} \approx 21.6$–23.0 mag (2$^{\prime\prime}$ diameter apertures; AB). The remaining eight targets are not detected to a median $3\unicode{x03C3}$ depth of $K_\textrm{s} \approx 23.3$ mag (2$^{\prime\prime}$ diameter apertures). We examine the radio and near-infrared flux densities of the 35 sources, comparing them to the known $z \gt 3$ powerful radio galaxies with 500-MHz radio luminosities $L_{500\,\textrm{MHz}} \gt 10^{27}$ W Hz$^{-1}$. By plotting 150-MHz flux density versus $K_\textrm{s}$-band flux density, we find that, similar to the sources from the literature, these new targets have large radio to near-infrared flux density ratios, but extending the distribution to fainter flux densities. Five of the eight HAWK-I deep non-detections have a median $3\unicode{x03C3}$ lower limit of $K_\textrm{s} \gtrsim 23.8$ mag (1$.\!^{\prime\prime}$5 diameter apertures); these five targets, along with a further source from Broderick et al. (2022, PASA, 39, e061) with a deep non-detection ($K_\textrm{s} \gtrsim 23.7$ mag; $3\unicode{x03C3}$; 2$^{\prime\prime}$ diameter aperture) in the Southern H-ATLAS Regions $K_\textrm{s}$-band Survey, are considered candidates to be ultra-high-redshift ($z \gt 5$) radio galaxies. The extreme radio to near-infrared flux density ratios ($\gt 10^5$) for these six sources are comparable to TN J0924$-$2201, GLEAM J0856$+$0223 and TGSS J1530$+$1049, the three known powerful radio galaxies at $z \gt 5$. For a selection of galaxy templates with different stellar masses, we show that $z \gtrsim 4.2$ is a plausible scenario for our ultra-high-redshift candidates if the stellar mass $M_\textrm{*} \gtrsim 10^{10.5}$ M$_\odot$. In general, the 35 targets studied have properties consistent with the previously known class of infrared-faint radio sources. We also discuss the prospects for finding more UHzRG candidates from wide and deep near-infrared surveys.

The radio interferometric closure phases can be a valuable tool for studying cosmological HI from the early Universe. Closure phases have the advantage of being immune to element-based gains and associated calibration errors. Thus, calibration and errors therein, which are often sources of systematics limiting standard visibility-based approaches, can be avoided altogether in closure phase analysis. In this work, we present the first results of the closure phase power spectrum of HI 21-cm fluctuations using the Murchison Widefield Array (MWA), with $\sim12$ h of MWA phase II observations centred around redshift, $z\approx 6.79$, during the Epoch of Reionisation. On analysing three redundant classes of baselines – 14, 24, and 28 m equilateral triads, our estimates of the $2\sigma$ (95% confidence interval) 21-cm power spectra are $\lesssim(184)^2 pseudo\,\mathrm{mK}^2$ at ${k}_{||} = 0.36 pseudo\ h \mathrm{Mpc}^{-1}$ in the EoR1 field for the 14 m baseline triads, and $\lesssim(188)^2 pseudo\,\mathrm{mK}^2$ at $k_{||} = 0.18 \,pseudo\ h \mathrm{Mpc}^{-1}$ in the EoR0 field for the 24 m baseline triads. The ‘pseudo’ units denote that the length scale and brightness temperature should be interpreted as close approximations. Our best estimates are still 3-4 orders high compared to the fiducial 21-cm power spectrum; however, our approach provides promising estimates of the power spectra even with a small amount of data. These data-limited estimates can be further improved if more datasets are included into the analysis. The evidence for excess noise has a possible origin in baseline-dependent systematics in the MWA data that will require careful baseline-based strategies to mitigate, even in standard visibility-based approaches.

We present high-resolution observations of nearby ($z\lesssim0.1$) galaxies that have hosted Type Ia supernovae to measure systemic spectroscopic redshifts using the wide field spectrograph (WiFeS) instrument on the Australian National University 2.3 m telescope at Siding Spring Observatory. While most of the galaxies targeted have previous spectroscopic redshifts, we provide demonstrably more accurate and precise redshifts with competitive uncertainties, motivated by potential systematic errors that could bias estimates of the Hubble constant ($H_0$). The WiFeS instrument is remarkably stable; after calibration, the wavelength solution varies by $\lesssim$0.5 Å in red and blue with no evidence of a trend over the course of several years. By virtue of the $25\times 38$ arcsec field of view, we are always able to measure the redshift of the galactic core, or the entire galaxy in the cases where its angular extent is smaller than the field of view, reducing any errors due to galaxy rotation. We observed 185 southern SN Ia host galaxies and measured the redshift of each via at least one spatial region of (a) the core and (b) the average over the full-field/entire galaxy. Overall, we find stochastic differences between historical redshifts and our measured redshifts on the order of $\lesssim10^{-3}$ with a mean offset of 4.3${\times 10^{-5}}$ and normalised median absolute deviation of 1.2${\times 10^{-4}}$. We show that a systematic redshift offset at this level is not enough to bias cosmology, as $H_0$ shifts by $+0.1$ km s$^{-1}$ Mpc$^{-1}$ when we replace Pantheon+ redshifts with our own, but the occasional large differences are interesting to note.

The proto-Milky Way epoch forms the earliest stars in our galaxy and sets the initial conditions for the subsequent disk formation. Recent observations showed that the [$\alpha$/Fe] ratio among in situ metal-poor stars declined between [Fe/H] $=-3$ and $-1.3$ until it reached the lowest value ($\sim$0.25) and rose to the traditional value associated with the high-[$\alpha$/Fe] thick disk ($\sim$0.3) at [Fe/H] $\approx$ -1.0. It was suggested that the rise in [$\alpha$/Fe] could be caused by an increase in the star formation efficiency (SFE), known as the ‘simmering’ phase scenario. However, gas inflow also plays a vital role in shaping the star formation history and chemical evolution of galaxies, especially during the earliest epoch of the universe. We investigate this unexpected [$\alpha$/Fe]-rise with an experiment involving a galactic chemical evolution model. Our model has five free parameters: the mass of the initial reservoir of the cold interstellar medium (ISM) at birth, the frequency of Type Ia supernovae (SNe Ia), the cooling timescale of the warm ISM, the SFE, and the inflow rate of fresh gas. The last two free parameters were allowed to change after [$\alpha$/Fe] reached its lowest value, dividing the proto-Galaxy epoch into two phases. The models that reproduced the observed [Fe/H]-[$\alpha$/Fe]-track provided estimates for these fundamental parameters of the proto-Milky Way. We find that the rise in [$\alpha$/Fe] could also be caused by a large inflow of high-[$\alpha$/Fe] gas and conclude that the [$\alpha$/Fe]-rise could be a signature of the gas accretion that fuelled the formation of the Milky Way disk.

In a poster presentation for IAU Symposium 392: “Neutral hydrogen in and around galaxies in the SKA era”, we gave an overview of the HI-MaNGA project which is working to obtain complementary information about the cold gas (neutral hydrogen traced by the radio 21cm line) content of Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) sample galaxies. MaNGA, part of the fourth incarnation of the Sloan Digital Sky Surveys (SDSS-IV), obtained spatially resolved spectral maps for 10,000 nearby galaxies selected to create a representative sample out of the SDSS Main Galaxy Sample. MaNGA data have provided a census of the stellar and ionized gas content of these galaxies, as well as kinematics of both stars and gas. Adding HI information via the HI-MaNGA program, which has observed or collected 21cm line data for 70% of the full MaNGA sample, has been crucial for a number of applications, but especially understanding the physical mechanisms that regulate gas accretion, and through that star formation and quenching of star formation.

We present our recent work on the simulation of the 21 cm interferometric signals by radio arrays for HI gas in galaxies at z = 0. We first introduce our recent developed software OmniUV, a toolkit to simulate the observational signals for interferometer arrays, which can offer the simulations for visibility data and image reconstructions. We use the HI gas outputs from Illustris-TNG to simulate the 21 cm signals of HI gas by radio arrays. We create the mock sky to mimic the observers coordinates and convert the HI mass to 21 cm flux. We adopt the configurations of SKA1-mid into OmniUV and generate the visibility data for HI gas in local universe, and also reconstruct the mock images based on the mock visibility data. Our work can help to test the observation strategies and target selections for HI sources by future interferometer arrays, like SKA, FASTA etc.

Connecting numerical simulations to observations is essential to understanding the physics of galactic winds. Our Galaxy hosts a large-scale, multi-phase nuclear wind, whose dense gas has been detected using H i and molecular line observations. In this paper, we summarise our recent numerical work devoted to producing synthetic H i observables and measuring the properties of H i gas in galactic wind simulations. We discuss the evolution of radiative cloud systems embedded in star formation-driven galactic winds. Our shock-multicloud models show that multicloud gas streams are able to produce significant fractions of H i gas via recondensation. Our wind-cloud models show that magnetic fields have significant effects on the morphology and spectral signatures of H i gas. Cooling-driven recondensation, hydrodynamic shielding, and magnetic draping promote the survival of dense gas and the development of filamentary outflows. The orientation of magnetic fields also has an effect on synthetic observables, particularly on H i spectral lines. Transverse magnetic fields produce broader spectral lines of H i than aligned magnetic fields. Our models and analysis suggest that the fast-moving H i gas observed in the nuclear wind of our Galaxy may arise from multi-phase flows via recondensation.

In this work, we peform a pilot study to investigate how the star formation rate history (SFRH) of galaxies relates to their neutral hydrogen gas (HI) mass. In particular we examine low redshift LADUMA galaxies and if this relation is dependent on redshift or galaxy morphologies. To do this we perform source finding over the LADUMA 0< z < 0.08 data cube, extract the multiwavelength photometry, then model the spectral energy distribution (SED) of each galaxy to obtain their SFRH.

Galaxy star formation rates (SFR), Hi masses, and H2 masses all show strong correlations with stellar mass for star-forming systems. Moreover, galaxies with high/low SFR also have high/low gas contents. Here we compare observations of correlated deviations off the main sequence from Janowiecki et al. to those in three galaxy formation simulations: Simba, EAGLE, and IllustrisTNG. Simulations predict that H2 deviations are linearly correlated with SFR deviations, as expected since star formation directly arises in dense gas. However, Hi deviations predictions vary, with Simba producing a near-linear slope but EAGLE and IllustrisTNG predicting sub-linear slopes. At earlier cosmic epochs, a sub-linear slope is always present in EAGLE and IllustrisTNG, but only at z = 2 in Simba, becoming linear at z ≤ 1. This suggests that the linear slope owes to the onset of AGN feedback, and hence that such feedback must remove Hi from the galaxy to match the observed linear slope. This provides unique insights into baryon cycling processes that connect gas within galaxies and their surroundings.

We present a search for HI 21 cm absorption associated with active galactic nuclei (AGN) using the SKA Precursor telescope MeerKAT. We use the latest data release from the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) HI survey [Heywood et al., 2024]. This data has a high spectral resolution of 26.1 kHz (∼8 kms−1) and wide bandwidth covering HI redshifts to z = 0.48. We have performed a targeted search for HI absorption along sight lines for the 181 radio galaxies in the COSMOS field within this redshift range. Our primary goal is to examine the interplay between gas, AGN fuelling and feedback, and the impact of these on the overall evolution of the host galaxies. The excellent sensitivity of both the MIGHTEE-HI and MIGHTEE-continuum data in this field allows us to examine lower radio power continuum sources than previously possible. We present 12 associated-HI absorption candidates.

The observed star formation rates in nearby galaxies suggest they are replenishing their gas reservoir over cosmic time. Cosmological simulations predict that this gas accretion can happen in two modes: hot and cold. However, direct observation of the low-column density (∼ 1017 cm−2) neutral atomic hydrogen (Hi) tracing the cold mode remains unconfirmed. Using the the spectral stacking technique on ultra-deep (∼1018 cm−2) Hi data provided by the MHONGOOSE survey we still found no clear evidence for the presence of the low-column density gas around nearby galaxies as predicted by simulations. We suggests that the gaseous disk has a sharp cut-off at large distances, consequently, detecting H i in the circum-galactic and inter-galactic medium could remain challenging, even with future advanced radio telescopes.

Ultra diffuse galaxies (UDGs) are a low surface brightness population of galaxies exhibiting large sizes. Their recent unexpected abundance in clusters has brought into question our understanding of galaxy evolution and the effect of the harsh cluster environment. Using MeerKAT HI observations of the Hydra I cluster, a nearby Southern galaxy cluster with ongoing galaxy interactions and evolution, we explore the neutral hydrogen content in low stellar mass galaxies, specifically investigating UDGs. Detailed observations of these galaxies in HI provide insights into the processes they experience in these harsh and dense environments. We present preliminary results on our search for UDGs in the Hydra cluster with MeerKAT, including HI detections of a UDG near the center of the cluster, a possible LSB galaxy and a dark cloud of neutral hydrogen.

We present the first MeerKAT observations of the brightest neutral hydrogen (HI) cloud in the M31-M33 HI filament [Braun Thilker(2004)] at a resolution of 40″. Our analysis unveils previously unseen details in the internal kinematic structure of the HI cloud. We measure NHI ≈ 1019 cm-2 in the cloud, an order of magnitude greater than previously observed, and recover approximately two-thirds of the previously measured MHI. We see signs of ram pressure stripping implying a particle number density of nHI ≈ 10-4 cm-3 in the circumgalactic medium (CGM) of M31. The cloud may also have been tidally disrupted by M31. Both results suggest that the HI cloud is being destroyed as it falls through the CGM of M31.

The advent of innovative new radio telescopes and instruments around the world has enabled HI observations of galaxies that are sharper, deeper, fainter and farther than ever before. This paper provides an overview of the extragalactic HI landscape today, with a focus on large surveys with SKA pathfinder facilities. Ongoing work to measure structural properties of HI disks from the WALLABY survey on the ASKAP telescope is also summarised, with an emphasis on the challenges of building statistical samples of the marginally detected and resolved systems that are characteristic of widefield untargetted surveys. This work paves the way to map HI disks across cosmic time with the SKA.