The cosmic 21 cm signal serves as a crucial probe for studying the evolutionary history of the Universe. However, detecting the 21 cm signal poses significant challenges due to its extremely faint nature. To mitigate the interference from the Earth’s radio frequency interference (RFI), the ground and the ionospheric effects, the Discovering the Sky at the Longest Wavelength (DSL) project will deploy a constellation of satellites in Lunar orbit, with its high-frequency daughter satellite tasked with detecting the global 21 cm signal from cosmic dawn and reionization era (CD/EoR).We intend to employ the Vari-Zeroth-Order Polynomial (VZOP) for foreground fitting and subtracting. We have studied the effect of thermal noise, thermal radiation from the Moon, the Lunar reflection, anisotropic frequency-dependent beam, inaccurate antenna beam pattern, and RFI contamination. We discovered that the RFI contamination can significantly affect the fitting process and thus prevent us from detecting the signal. Therefore, experimenting on the far side of the moon is crucial. We also discovered that using VZOP together with DSL, after 1080 orbits around the Moon, which takes about 103 days, we can successfully detect the CD/EoR 21 cm signal.

AstroSat observed transient neutron star low-mass X-ray binary XTE J1701-462 for a total duration of ∼ 135 ks during its 2022 outburst. We report the results of a detailed spectral and timing analysis carried out using this data. The source traced a complete ‘Z’ shaped structure in the hardness intensity diagram (HID). The source exhibited an extended horizontal branch and a short-dipping flaring branch in the HID. The spectra of the source were fitted with different approaches. We find that most suitable spectral model comprises emission from a standard multi-color accretion disk (diskbb in XSPEC) and Comptonized radiation from a hot central corona, described by Comptb model of XSPEC. The observed disk component is cool, having a temperature in the range of ∼ 0.28 – 0.42 keV and truncated far (∼ 250 - 1600 km) from the compact object. The Compton corona has an optical depth in the range of ∼ 3.4 – 5.1 and a temperature in the range of 3.3 – 4.5 keV. The disk and corona flux as well as truncation radius vary significantly along the HID. The temperature kTin depends on both luminosity and inner disk radius and hence shows marginal variation as compared to the truncation radius. We discuss possible scenarios to explain the relationship between the spectral evolution and motion of the source along the HID. The timing analysis revealed horizontal branch oscillations (HBOs) in the frequency range ∼ 34 – 40 Hz. The frequency and rms strength of HBO vary systematically as the source moves along the horizontal branch (HB). The observed correlation of the HBO properties with the position on the HB is similar to that previously reported in this source using RXTE data during the 2006 outburst of the source. The source also showed normal branch oscillations (NBOs) with frequency ∼ 6.7 Hz in the middle and the lower normal branch. The energy-dependent study of the HBO properties suggests that the HBO is stronger in the higher energy band. We also observed very-low frequency noise (VLFN) and band-limited noise (BLN) components in the power density spectra. The break frequency of BLN component was found to be tightly correlated with the HBO frequency. We discuss possible models to explain the origin and nature of the observed features in the PDS.

The stellar age and mass of galaxies have been suggested as the primary determinants for the dynamical state of galaxies, with environment seemingly playing no or only a very minor role. We use a sample of 77 galaxies at intermediate redshift ($z\sim0.3$) in the Middle-Ages Galaxies Properties with Integral field spectroscopy (MAGPI) Survey to study the subtle impact of environment on galaxy dynamics. We use a combination of statistical techniques (simple and partial correlations and principal component analysis) to isolate the contribution of environment on galaxy dynamics, while explicitly accounting for known factors such as stellar age, star formation histories, and stellar masses. We consider these dynamical parameters: high-order kinematics of the line-of-sight velocity distribution (parametrised by the Gauss-Hermite coefficients $h_3$ and $h_4$), kinematic asymmetries $V_{\textrm{asym}}$ derived using kinemetry, and the observational spin parameter proxy $\lambda_{R_e}$. Of these, the mean $h_4$ is the only parameter found to have a significant correlation with environment as parametrised by group dynamical mass. This correlation exists even after accounting for age and stellar mass trends. We also find that satellite and central galaxies exhibit distinct dynamical behaviours, suggesting they are dynamically distinct classes. Finally, we confirm that variations in the spin parameter $\lambda_{R_e}$ are most strongly (anti-)correlated with age as seen in local studies, and show that this dependence is well-established by $z\sim0.3$.

Galaxy cluster X-ray cavities are inflated by relativistic jets that are ejected into the intracluster medium by active galactic nuclei (AGN). AGN jets prevent predicted cooling flow establishment at the cluster centre, and while this process is not well understood in existing studies, simulations have shown that the heating mechanism will depend on the type of gas that fills the cavities. Thermal and non-thermal distributions of electrons will produce different cavity Sunyaev Zel’dovich (SZ) effect signals, quantified by the ‘suppression factor’ f. This paper explores potential enhancements to prior constraints on the cavity gas type by simulating suppression factor observations with the Square Kilometre Array (SKA). Cluster cavities across different redshifts are observed to predict the optimum way of measuring f in future observations. We find that the SKA can constrain the suppression factor in the cavities of cluster MS 0735.6+7421 (MS0735) in as little as 4 h, with a smallest observable value of $f \approx 0.42$. Additionally, while the SKA may distinguish between possible thermal or non-thermal suppression factor values within the cavities of MS0735 if it observes for more than 8 h, determining the gas type of other clusters will likely require observations at multiple frequencies. The effect of cavity line of sight (LOS) position is also studied, and degeneracies between LOS position and the measured value of f are found. Finally, we find that for small cavities (radius < 80 kpc) at high redshift ($z \approx 1.5$), the proposed high frequencies of the SKA (23.75–37.5 GHz) will be optimal, and that including MeerKAT antennas will improve all observations of this type.

Over a hundred gravitational-wave signals have now been detected from the mergers of black holes and neutron stars, but other sources of gravitational waves have not yet been discovered. Some of the most violent explosive events in the Universe are predicted to emit bursts of gravitational waves and may result in the next big multi-messenger discovery. Gravitational-wave burst signals often have an unknown waveform shape and unknown gravitational-wave energy, due to unknown or very complicated progenitor astrophysics. Potential sources of gravitational-wave bursts include core-collapse supernovae, cosmic strings, fast radio bursts, eccentric binary systems, and gravitational-wave memory. In this review, we discuss the astrophysical properties of the main predicted sources of gravitational-wave bursts and the known features of their gravitational-wave emission. We summarise their future detection prospects and discuss the challenges of searching for gravitational-wave burst signals and interpreting the astrophysics of the source.

We propose that certain white dwarf (WD) planets, such as WD 1856+534 b, may form out of material from a stellar companion that tidally disrupts from common envelope evolution with the WD progenitor star. The disrupted companion shreds into an accretion disc, out of which a gas giant protoplanet forms due to gravitational instability. To explore this scenario, we make use of detailed stellar evolution models consistent with WD 1856+534. The minimum mass companion that produces a gravitationally unstable disc after tidal disruption is $\sim$$0.15\,\mathrm{M_\odot}$. In this scenario, WD 1856+534 b might have formed at or close to its present separation, in contrast to other proposed scenarios where it would have migrated in from a much larger separation. Planet formation from tidal disruption is a new channel for producing second-generation planets around WDs.

Detection of the weak cosmological signal from high-redshift hydrogen demands careful data analysis and an understanding of the full instrument signal chain. Here, we use the WODEN simulation pipeline to produce realistic data from the Murchison Widefield Array (MWA) Epoch of Reionisation experiment and test the effects of different instrumental systematics through the AusEoRPipe analysis pipeline. The simulations include a realistic full sky model, direction-independent calibration, and both random and systematic instrumental effects. Results are compared to matched real observations. We find that, (i) with a sky-based calibration and power spectrum approach we have need to subtract more than 90% of all unresolved point source flux (10 mJy apparent) to recover 21-cm signal in the absence of instrumental effects; (ii) when including diffuse emission in simulations, some k-modes cannot be accessed, leading to a need for some diffuse emission removal; (iii) the single greatest cause of leakage is an incomplete sky model; and (iv) other sources of errors, such as cable reflections, flagged channels, and gain errors, impart comparable systematic power to one another and less power than the incomplete sky model.

Radio-frequency interference (RFI) presents a significant obstacle to current radio interferometry experiments aimed at the Epoch of Reionization. RFI contamination is often several orders of magnitude brighter than the astrophysical signals of interest, necessitating highly precise identification and flagging. Although existing RFI flagging tools have achieved some success, the pervasive nature of this contamination leads to the rejection of excessive data volumes. In this work, we present a way to estimate an RFI emitter’s altitude using near-field corrections. Being able to obtain the precise location of such an emitter could shift the strategy from merely flagging to subtracting or peeling the RFI, allowing us to preserve a higher fraction of usable data. We conduct a preliminary study using a two-minute observation from the Murchison-Widefield Array (MWA) in which an unknown object briefly crosses the field of view, reflecting RFI signals into the array. By applying near-field corrections that bring the object into focus, we are able to estimate its approximate altitude and speed to be $11.7$ km and 792 km/h, respectively. This allows us to confidently conclude that the object in question is in fact an airplane. We further validate our technique through the analysis of two additional RFI-containing MWA observations, where we are consistently able to identify airplanes as the source of the interference.

We present a new radio detection from the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe (EMU) survey associated with the Reflection Nebula (RN) VdB-80. The radio detection is determined to be a previously unidentified Hii region, now named Lagotis. The RN is located towards Monoceros, centred in the molecular cloud feature known as the ‘Crossbones’. The 944 MHz EMU image shows a roughly semicircular Hii region with an integrated flux density of 30.2$\pm$0.3 mJy. The Hii region is also seen at 1.4 GHz by NRAO VLA Sky Survey (NVSS), yielding an estimated spectral index of 0.65$\pm$0.51, consistent with thermal radio emission. Gaia Data Release 3 (DR3) and Two Micron All Sky Survey (2MASS) data give a distance to the stars associated with the Hii region of $\sim$960 pc. This implies a size of 0.76$\times$0.68($\pm$0.09) pc for the Hii region. We derive an Hii region electron density of the bright radio feature to be 26 cm$^{-3}$, requiring a Lyman-alpha photon flux of $10^{45.6}$ s$^{-1}$, which is consistent with the expected Lyman flux of HD 46060, the B2 ii type star which is the likely ionising star of the region. The derived distance to this region implies that the Crossbones feature is a superposition of two filamentary clouds, with Lagotis embedded in the far cloud.

The 2175Å bump is a prominent absorption feature at ultraviolet (UV) wavelengths in dust extinction and attenuation curves. Understanding the relative strength of this feature is important for making accurate dust corrections at both low- and high-redshift. This feature is postulated to arise from polycyclic aromatic hydrocarbon (PAH) dust grains; however, the carrier has not been definitively established. We present results on the correlation between the 2175Å feature and PAH abundances in a spatially-resolved manner for 15 local galaxies in the PHANGS-JWST survey that have NUV and mid-IR imaging data from Swift/UVOT and JWST/MIRI, respectively. We find a moderate positive correlation between the 2175Å feature strength and PAH abundance (Spearman’s coefficient, $0.3 \lesssim \rho \lesssim 0.5$), albeit with large intrinsic scatter. However, most of this trend can be attributed to a stronger negative correlation of both quantities with SFR surface density and specific-SFR (proxies of ionising radiation; $\rho\sim-0.6$). The latter trends are consistent with previous findings that both the 2175Å carrier and PAHs are small grains that are easily destroyed by UV photons, although the proxy for PAH abundance (based on photometry) could also be influenced by dust heating. When controlling for SFR surface density, we find weaker correlations between the 2175Å feature and PAH abundances ($\rho \lesssim 0.3$), disfavouring a direct link. However, analyses based on spectroscopic (instead of photometric) measurements of the 2175Å feature and PAH features are required to verify our findings. No significant trends with gas-phase metallicity or galactocentric radii are found for the 2175Å feature and PAHs; however, the metallicity range of our sample is limited ($8.40 \lt 12+\log[\mathrm{O/H}] \lt 8.65$). We provide prescriptions for the strength of the 2175Å feature and PAHs in local massive (metal-rich) galaxies with SFR surface density and specific-SFR; however, the former should be used with caution due to the fact that bump strengths measured from Swift/UVOT are expected to be underestimated.

The data volumes generated by theWidefield ASKAP L-band Legacy All-sky Blind surveY atomic hydrogen (Hi) survey using the Australian Square Kilometre Array Pathfinder (ASKAP) necessitate greater automation and reliable automation in the task of source finding and cataloguing. To this end, we introduce and explore a novel deep learning framework for detecting low signal-to-noise ratio (SNR) Hi sources in an automated fashion. Specifically, our proposed method provides an automated process for separating true Hi detections from false positives when used in combination with the source finding application output candidate catalogues. Leveraging the spatial and depth capabilities of 3D convolutional neural networks, our method is specifically designed to recognize patterns and features in three-dimensional space, making it uniquely suited for rejecting false-positive sources in low SNR scenarios generated by conventional linear methods. As a result, our approach is significantly more accurate in source detection and results in considerably fewer false detections compared to previous linear statistics-based source finding algorithms. Performance tests using mock galaxies injected into real ASKAP data cubes reveal our method’s capability to achieve near-100% completeness and reliability at a relatively low integrated SNR $\sim3-5$. An at-scale version of this tool will greatly maximise the science output from the upcoming widefield Hi surveys.

Asymptotic giant branch (AGB) stars play a significant role in our understanding of the origin of the elements. They contribute to the abundances of C, N, and approximately 50% of the abundances of the elements heavier than iron. An aspect often neglected in studies of AGB stars is the impact of a stellar companion on AGB stellar evolution and nucleosynthesis. In this study, we update the stellar abundances of AGB stars in the binary population synthesis code binary_c and calibrate our treatment of the third dredge-up using observations of Galactic carbon stars. We model stellar populations of low- to intermediate-mass stars at solar-metallicity and examine the stellar wind contributions to C, N, O, Sr, Ba, and Pb yields at binary fractions between 0 and 1. For a stellar population with a binary fraction of 0.7, we find $\sim$20–25% less C and s-process elements ejected than from a population composed of only single stars, and we find little change in the N and O yields. We also compare our models with observed abundances from Ba stars and find our models can reproduce most Ba star abundances, but our population estimates a higher frequency of Ba stars with a surface [Ce/Y] > $+0.2\,$dex. Our models also predict the rare existence of Ba stars with masses $ \gt 10\,\textrm{M}_{\odot}$.

The initial mass function (IMF) is a construct that describes the distribution of stellar masses for a newly formed population of stars. It is a fundamental element underlying all of star and galaxy formation and has been the subject of extensive investigation for more than 60 yr. In the past few decades, there has been a growing, and now substantial, body of evidence supporting the need for a variable IMF. In this light, it is crucial to investigate the IMF’s characteristics across different spatial scales and to understand the factors driving its variability. We make use of spatially resolved spectroscopy to examine the high-mass IMF slope of star-forming galaxies within the SAMI survey. By applying the Kennicutt method and stellar population synthesis models, we estimated both the spaxel-resolved ($\alpha_{res}$) and galaxy-integrated ($\alpha_{int}$) high-mass IMF slopes of these galaxies. Our findings indicate that the resolved and integrated IMF slopes exhibit a near 1:1 relationship for $\alpha_{int}\gtrsim -2.7$. We observe a wide range of $\alpha_{res}$ distributions within galaxies. To explore the sources of this variability, we analyse the relationships between the resolved and integrated IMF slopes and both the star formation rate (SFR) and SFR surface density ($\Sigma_{\textrm{SFR}}$). Our results reveal a strong correlation where flatter/steeper slopes are associated with higher/lower SFR and $\Sigma_{\textrm{SFR}}$. This trend is qualitatively similar for resolved and global scales. Additionally, we identify a mass dependency in the relationship with SFR, though none was found in the relation between the resolved slope and $\Sigma_{\textrm{SFR}}$. These findings suggest an scenario where the formation of high-mass stars is favoured in regions with more concentrated star formation. This may be a consequence of the reduced fragmentation of molecular clouds, which nonetheless accrete more material.

We have carried out a detailed investigation of eclipsing binary star NT Aps using high cadence photometric observations from the TESS satellite and time-series spectra from EFOSC2 at ESO’s New Technology Telescope.a We have, for the first time, determined precise system parameters for this W UMa-type late-type contact binary. Our analysis indicates that the system is composed of two solar-like stars with mass ratio of $q=0.31$ and orbital period of 0.29475540 $\pm$ 0.00000035 days. These values are typical for common envelope contact binaries. However, the system does not exhibit strong magnetic activity in the form of frequent flaring and large starspots, even if large flare rates have been earlier predicted for this system. This lack of strong magnetic activity further strengthens the earlier indications that the contact binaries are less magnetically active than those of detached chromospherically active binaries with similar parameters.

We present the first results from a new backend on the Australian Square Kilometre Array Pathfinder, the Commensal Realtime ASKAP Fast Transient COherent (CRACO) upgrade. CRACO records millisecond time resolution visibility data, and searches for dispersed fast transient signals including fast radio bursts (FRB), pulsars, and ultra-long period objects (ULPO). With the visibility data, CRACO can localise the transient events to arcsecond-level precision after the detection. Here, we describe the CRACO system and report the result from a sky survey carried out by CRACO at 110-ms resolution during its commissioning phase. During the survey, CRACO detected two FRBs (including one discovered solely with CRACO, FRB 20231027A), reported more precise localisations for four pulsars, discovered two new RRATs, and detected one known ULPO, GPM J1839 $-$10, through its sub-pulse structure. We present a sensitivity calibration of CRACO, finding that it achieves the expected sensitivity of 11.6 Jy ms to bursts of 110 ms duration or less. CRACO is currently running at a 13.8 ms time resolution and aims at a 1.7 ms time resolution before the end of 2024. The planned CRACO has an expected sensitivity of 1.5 Jy ms to bursts of 1.7 ms duration or less and can detect $10\times$ more FRBs than the current CRAFT incoherent sum system (i.e. 0.5 $-$2 localised FRBs per day), enabling us to better constrain the models for FRBs and use them as cosmological probes.

Spiral galaxies are ubiquitous in the local Universe. However, the properties of spiral arms in them are still not well studied, and there is even less information concerning spiral structure in distant galaxies. We aim to measure the most general parameters of spiral arms in remote galaxies and trace their changes with redshift. We perform photometric decomposition, including spiral arms, for 159 galaxies from the HST COSMOS and JWST CEERS and JADES surveys, which are imaged in optical and near-infrared rest-frame wavelengths. We confirm that, in our representative sample of spiral galaxies, the pitch angles increase, and the azimuthal lengths decrease with increasing redshift, implying that the spiral structure becomes more tightly wound over time. For the spiral-to-total luminosity ratio and the spiral width-to-disc scale length ratio, we find that band-shifting effects can be as significant as, or even stronger than, evolutionary effects. Additionally, we find that spiral structure becomes more asymmetric at higher redshifts.

We introduce adaptive particle refinement for compressible smoothed particle hydrodynamics (SPH). SPH calculations have the natural advantage that resolution follows mass, but this is not always optimal. Our implementation allows the user to specify local regions of the simulation that can be more highly resolved. We test our implementation on practical applications including a circumbinary disc, a planet embedded in a disc, and a flyby. By comparing with equivalent globally high-resolution calculations, we show that our method is accurate and fast, with errors in the mass accreted onto sinks of less than 9% and speed ups of 1.07–6.62$\times$ for the examples shown. Our method is adaptable and easily extendable, for example, with multiple refinement regions or derefinement.

Galaxy morphology in stellar light can be described by a series of ‘non-parametric’ or ‘morphometric’ parameters, such as concentration-asymmetry-smoothness, Gini, $M_{20}$, and Sérsic fit. These parameters can be applied to column density maps of atomic hydrogen (H 1). The H 1 distribution is susceptible to perturbations by environmental effects, for example, intergalactic medium pressure and tidal interactions. Therefore, H 1 morphology can potentially identify galaxies undergoing ram-pressure stripping or tidal interactions. We explore three fields in the WALLABY Pilot H 1 survey and identify perturbed galaxies based on a k-nearest neighbour (kNN) algorithm using an H 1 morphometric feature space. For training, we used labelled galaxies in the combined NGC 4808 and NGC 4636 fields with six H 1 morphometrics to train and test a kNN classifier. The kNN classification is proficient in classifying perturbed galaxies with all metrics – accuracy, precision, and recall – at 70–80%. By using the kNN method to identify perturbed galaxies in the deployment field, the NGC 5044 mosaic, we find that in most regards, the scaling relations of perturbed and unperturbed galaxies have similar distribution in the scaling relations of stellar mass versus star formation rate and the Baryonic Tully–Fisher relation, but the H 1 and stellar mass relation flatter than of the unperturbed galaxies. Our results for NGC 5044 provide a prediction for future studies on the fraction of galaxies undergoing interaction in this catalogue and to build a training sample to classify such galaxies in the full WALLABY survey.

We present the results of searching for new dwarf galaxies in the Local Volume. We found 40 satellite candidates in the double-virial-radius regions of 20 Milky Way-like and Large Magellanic Cloud (LMC)-like galaxies in the southern sky using DESI Legacy Imaging Surveys, 10 of which were known but not clearly associated with the Local Volume previously. Among the 40 satellite candidates, 8 are supposed members of the NGC 6744 group and 13 are located in the vicinity of the Sombrero galaxy. Based on seven companions to the giant spiral galaxy NGC 6744 with measured radial velocities, we estimate that the total mass of the group is $M_T = (1.88\pm0.71)\times 10^{12}\,\mathrm{M}_{\odot}$ and the total mass-to-K-luminosity ratio $M_T/L_K = (16.1\pm6.0) \mathrm{M}_{\odot}/\mathrm{L}_{\odot}$. We reproduce a distribution of 68 early- and late-type galaxies in the Local Volume situated around the Sombrero, noting their strong morphological segregation and also the presence of a foreground diffuse association of dwarf galaxies at 8 degrees to SE from the Sombrero.

Next generations of radio surveys are expected to identify tens of millions of new sources and identifying and classifying their morphologies will require novel and more efficient methods. Self-organising maps (SOMs), a type of unsupervised machine learning, can be used to address this problem. We map 251 259 multi-Gaussian sources from Rapid ASKAP Continuum Survey (RACS) onto a SOM with discrete neurons. Similarity metrics, such as Euclidean distances, can be used to identify the best-matching neuron or unit (BMU) for each input image. We establish a reliability threshold by visually inspecting a subset of input images and their corresponding BMU. We label the individual neurons based on observed morphologies, and these labels are included in our value-added catalogue of RACS sources. Sources for which the Euclidean distance to their BMU is $\lesssim$5 (accounting for approximately 79$\%$ of sources) have an estimated $ \gt $90% reliability for their SOM-derived morphological labels. This reliability falls to less than 70$\%$ at Euclidean distances $\gtrsim$7. Beyond this threshold it is unlikely that the morphological label will accurately describe a given source. Our catalogue of complex radio sources from RACS with their SOM-derived morphological labels from this work will be made publicly available.