Trends in elemental enrichment with stellar age can give us a powerful avenue to identify thus far unexplained origin sites of the elements. We investigate stellar abundance trends using the GALAH DR3 high-resolution spectroscopic dataset of 6 234 solar-type stars. Our study explores the elemental abundance [X/Fe] of sodium (Na) with stellar age. We find a pronounced enrichment in [Na/Fe] at super solar metallicity (i.e. [Fe/H] $ \gt \,0$) in the old sequence of Milky Way disc stars, a trend demanding a deeper understanding of the underlying source(s) responsible for the nucleosynthesis. This progressive [Na/Fe] enrichment at the young end of the old sequence has essential implications for Galactic archaeology. In this work, we propose a novel selection technique for separating the Milky Way’s thick and thin disc stellar populations (i.e. old and young sequences) based on the observed [Na/Fe] rise of $\sim$0.1 dex for stars around 5–8 Gyr old. We also compare our selection method to the conventional [Mg/Fe] vs. [Fe/H] selection approach, and we find that our new Na-based selection method better disentangles the overlap between young- and old-sequence disc stars at these intermediate ages. This is especially true at super solar [Fe/H], where the [Mg/Fe] vs. [Fe/H] or [$\alpha$/Fe] vs. [Fe/H] separation approaches exhibit significant overlap. This new selection method should help us better understand the history of the formation of the Milky Way disc.

Environment has long been known to have an impact on the evolution of galaxies, but disentangling its impact from mass evolution requires the careful analysis of statistically significant samples. By implementing cutting-edge visualisation methods to test and validate group-finding algorithms, we utilise a mass-complete sample of galaxies to z < 0.1 comprised of spectroscopic redshifts from prominent surveys such as the 2-degree Field Galaxy Redshift Survey and the Galaxy and Mass Assembly Survey. Utilising our group finding methods, we find 1,413 galaxy groups made up of 8,990 galaxies corresponding to 36% of galaxies associated with group environments. We also search for close pairs, with separations of rsep < 50 h−1kpc and vsep < 500 km s−1 within our sample and further classified them into major (Msec/Mprim ≤ 0.25) and minor (Msec/Mprim > 0.25) pairs. To examine the impact of environmental factors, we employ bespoke WISE photometry, which facilitates accurate measurements of stellar mass and star formation rates and hence the best possible description of the variation of galaxy properties as a function of the local environment. Our analysis, employing a derived star-forming main sequence relation, reveals that star-formation (SF) within galaxies are pre-processed as a function of group membership. This is evident from the evolution of the star-forming and quenched population of galaxies. We see an increase in the fraction of quiescent galaxies relative to the field as group membership increases and this excess of quenched galaxies relative to the field is later quantified through the use of the environmental quenching efficiency (εenv) metric. Within the star-forming population, we observe SF pre-processing with the relative difference in specific star formation rates (∆sSFR), where we see a net decrease in SF as group membership increases, particularly at larger stellar masses. We again quantify this change within the SF population with our star formation deficiency (εSFD) metric. Our sample of close pairs at low stellar masses exhibit enhanced star formation efficiencies compared to the field, and at larger stellar mass ranges show large deficiencies. Separating the close pairs into major/minors and primary/secondaries reveals SF enhancements projected separation decreases within the minor pairs, this effect is even more pronounced within minor primaries. This research emphasises the importance of carefully studying the properties of galaxies within group environments to better understand the pre-processing of SF within galaxies. Our results show that the small-scale environments of galaxies influence star-forming properties even when stellar masses are kept constant. This demonstrates that galaxies do not evolve in isolation over cosmic time but are shaped by a complex interaction between their internal dynamics and external influences.

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.

We present source detection and catalogue construction pipelines to build the first catalogue of radio galaxies from the 270 $\rm deg^2$ pilot survey of the Evolutionary Map of the Universe (EMU-PS) conducted with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The detection pipeline uses Gal-DINO computer vision networks (Gupta et al. 2024, PASA, 41, e001) to predict the categories of radio morphology and bounding boxes for radio sources, as well as their potential infrared host positions. The Gal-DINO network is trained and evaluated on approximately 5 000 visually inspected radio galaxies and their infrared hosts, encompassing both compact and extended radio morphologies. We find that the Intersection over Union (IoU) for the predicted and ground-truth bounding boxes is larger than 0.5 for 99% of the radio sources, and 98% of predicted host positions are within $3^{\prime \prime}$ of the ground-truth infrared host in the evaluation set. The catalogue construction pipeline uses the predictions of the trained network on the radio and infrared image cutouts based on the catalogue of radio components identified using the Selavy source finder algorithm. Confidence scores of the predictions are then used to prioritise Selavy components with higher scores and incorporate them first into the catalogue. This results in identifications for a total of 211 625 radio sources, with 201 211 classified as compact and unresolved. The remaining 10 414 are categorised as extended radio morphologies, including 582 FR-I, 5 602 FR-II, 1 494 FR-x (uncertain whether FR-I or FR-II), 2 375 R (single-peak resolved) radio galaxies, and 361 with peculiar and other rare morphologies. Each source in the catalogue includes a confidence score. We cross-match the radio sources in the catalogue with the infrared and optical catalogues, finding infrared cross-matches for 73% and photometric redshifts for 36% of the radio galaxies. The EMU-PS catalogue and the detection pipelines presented here will be used towards constructing catalogues for the main EMU survey covering the full southern sky.

Creating radio galaxy catalogues from next-generation deep surveys requires automated identification of associated components of extended sources and their corresponding infrared hosts. In this paper, we introduce RadioGalaxyNET, a multimodal dataset, and a suite of novel computer vision algorithms designed to automate the detection and localization of multi-component extended radio galaxies and their corresponding infrared hosts. The dataset comprises 4 155 instances of galaxies in 2 800 images with both radio and infrared channels. Each instance provides information about the extended radio galaxy class, its corresponding bounding box encompassing all components, the pixel-level segmentation mask, and the keypoint position of its corresponding infrared host galaxy. RadioGalaxyNET is the first dataset to include images from the highly sensitive Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope, corresponding infrared images, and instance-level annotations for galaxy detection. We benchmark several object detection algorithms on the dataset and propose a novel multimodal approach to simultaneously detect radio galaxies and the positions of infrared hosts.

Recent studies of Galactic evolution revealed that the dynamics of the stellar component might be one of the key factors when considering galactic habitability. We run an N-body simulation model of the Milky Way, which we evolve for 10 Gyr, to study the secular evolution of stellar orbits and the resulting galactic habitability related properties, i.e., the density of the stellar component and close stellar encounters. The results indicate that radial migrations are not negligible, even in a simple axisymmetric model with mild levels of dynamical heating, and that the net outward diffusion of the stellar component can populate galactic outskirts with habitable systems. Habitable environment is also likely even at sub-Solar galactocentric radii, because the rate of close encounters should not significantly degrade habitability. Stars that evolve from non-circular to stable nearly circular orbits typically migrate outwards, settling down in a broad Solar neighbourhood. The region between $R \approx 3$ kpc and $R \approx 12$ kpc represents the zone of radial mixing, which can blur the boundaries of the Galactic Habitable Zone (GHZ), as it has been conventionally understood. The present-day stable population of the stars in the Solar neighbourhood originates from this radial mixing zone, with most of the stars coming from the inner regions. The Solar system can be considered as a typical Milky Way habitable system because it migrated outwards from the metal-rich inner regions of the Disk and has a circular orbit in the present epoch. We conclude that the boundaries of the GHZ cannot be sharply confined for a given epoch because of the mixing caused by the stellar migrations and secular evolution of stellar orbits.

The present work discusses the use of a weakly-supervised deep learning algorithm that reduces the cost of labelling pixel-level masks for complex radio galaxies with multiple components. The algorithm is trained on weak class-level labels of radio galaxies to get class activation maps (CAMs). The CAMs are further refined using an inter-pixel relations network (IRNet) to get instance segmentation masks over radio galaxies and the positions of their infrared hosts. We use data from the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, specifically the Evolutionary Map of the Universe (EMU) Pilot Survey, which covered a sky area of 270 square degrees with an RMS sensitivity of 25–35 $\mu$Jy beam$^{-1}$. We demonstrate that weakly-supervised deep learning algorithms can achieve high accuracy in predicting pixel-level information, including masks for the extended radio emission encapsulating all galaxy components and the positions of the infrared host galaxies. We evaluate the performance of our method using mean Average Precision (mAP) across multiple classes at a standard intersection over union (IoU) threshold of 0.5. We show that the model achieves a mAP$_{50}$ of 67.5% and 76.8% for radio masks and infrared host positions, respectively. The network architecture can be found at the following link: https://github.com/Nikhel1/Gal-CAM

The investigation of the metal-poor tail in the Galactic bulge provides unique information on the early Milky Way assembly and evolution. A chemo-dynamical analysis of 17 very metal-poor stars (VMP, [Fe/H < – 2.0]) selected from the Pristine Inner Galaxy Survey was carried out based on Gemini/GRACES spectra. The chemistry suggests that the majority of our stars are very similar to metal-poor stars in the Galactic halo. Orbits calculated from Gaia EDR3 imply these stars are brought into the bulge during the earliest Galactic assembly. Most of our stars have large [Na,Ca/Mg] abundances, and thus show little evidence of enrichment by pair-instability supernovae. Two of our stars (P171457, P184700) have chemical abundances compatible with second-generation globular cluster stars, suggestive of the presence of ancient and now dissolved globular clusters in the inner Galaxy. One of them (P171457) is extremely metal-poor ([Fe/H < – 3.0]) and well below the metallicity floor of globular clusters, which supports the growing evidence for the existence of lower-metallicity globular clusters in the early Universe. A third star (P180956, [Fe/H]∼ – 2) has low [Na,Ca/Mg] and very low [Ba/Fe] for its metallicity, which are consistent with formation in a system polluted by only one or a few low-mass supernovae. Interestingly, its orbit is confined to the Galactic plane, like other very metal-poor stars found in the literature, which have been associated with the earliest building blocks of the Milky Way.

Dramatic recent progress in understanding galactic chemical evolution (GCE) has been driven partly by direct observations of the distant past with HST and JWST and partly by archeaological interpretation of stellar abundances from giant high-resolution spectroscopic surveys (APOGEE, GALAH) and the complementary power of Gaia astrometry and photometry. Focusing on archaeology, I give a rapid-fire, and I hope synthesizing, review of work my collaborators and I have done on theoretical modeling and observational interpretation. I discuss (1) the interleaved but distinguishable roles of stellar scale astrophysics and galactic scale astrophysics in governing GCE, (2) the use of abundance ratio trends to empirically infer nucleosynthetic yields, (3) the uncertainty in the overall scale of yields and its degeneracy with the importance of galactic outflows, (4) the emergence of equilibrium in GCE, (5) the dimensionality of the stellar distribution in chemical abundance space, and (6) insights from chemical abundances on the early history of the Milky Way, including measurements of the intrinsic scatter of abundance ratios in metal-poor stars (-2≤[Fe/H] ≤-1) suggesting that a typical halo star at this metallicity is enriched by the products of N∼50 supernovae mixed over ∼105M⊚ of star-forming gas.

We present GECKOS (Generalising Edge-on galaxies and their Chemical bimodalities, Kinematics, and Outflows out to Solar environments), a new ESO VLT/MUSE large program. The main aim of GECKOS is to reveal the variation in key physical processes of disk formation by connecting Galactic Archaeology with integral field spectroscopic observations of nearby galaxies. Edge-on galaxies are ideal for this task: they allow us to disentangle the assembly history imprinted in thick disks and provide the greatest insights into outflows. The GECKOS sample of 35 nearby edge-on disk galaxies is designed to trace the assembly histories and properties of galaxies across a large range of star formation rates, bulge-to-total ratios, and boxy and non-boxy bulges. GECKOS will deliver spatially resolved measurements of stellar abundances, ages, and kinematics, as well as ionised gas metallicities, ionisation param- eters, pressure, and inflow and outflow kinematics; all key parameters for building a complete chemodynamical picture of disk galaxies. With these data, we aim to extend Galactic analysis methods to the wider galaxy population, reaping the benefits of detailed Milky Way studies, while probing the diverse mechanisms of galaxy evolution.

The chemo-dynamics of the stellar populations in the Galactic Bulge inform and constrain the Milky Way’s formation and evolution. The metal-poor population is particularly important in light of cosmological simulations, which predict that some of the oldest stars in the Galaxy now reside in its center. The metal-poor bulge appears to consist of multiple stellar populations that require chemo-dynamical analyses to disentangle. In this paper, I describe the detailed chemo-dynamical study of the metal-poor stars in the inner Galaxy, named The COMBS Survey which uses VLT/FLAMES spectra of 350 metal-poor stars. I discuss the results and the implications for early Milky Way formation and chemical evolution. In addition, I preview results from an ongoing survey of carbon-enhanced metal-poor stars, which are thought to be solely enriched by the first generation of stars.

We present a set of peculiar radio sources detected using an unsupervised machine learning method. We use data from the Australian Square Kilometre Array Pathfinder (ASKAP) telescope to train a self-organizing map (SOM). The radio maps from three ASKAP surveys, Evolutionary Map of Universe pilot survey (EMU-PS), Deep Investigation of Neutral Gas Origins pilot survey (DINGO), and Survey With ASKAP of GAMA-09 + X-ray (SWAG-X), are used to search for the rarest or unknown radio morphologies. We use an extension of the SOM algorithm that implements rotation and flipping invariance on astronomical sources. The SOM is trained using the images of all ‘complex’ radio sources in the EMU-PS which we define as all sources catalogued as ‘multi-component’. The trained SOM is then used to estimate a similarity score for complex sources in all surveys. We select 0.5% of the sources that are most complex according to the similarity metric and visually examine them to find the rarest radio morphologies. Among these, we find two new odd radio circle (ORC) candidates and five other peculiar morphologies. We discuss multiwavelength properties and the optical/infrared counterparts of selected peculiar sources. In addition, we present examples of conventional radio morphologies including: diffuse emission from galaxy clusters, and resolved, bent-tailed, and FR-I and FR-II type radio galaxies. We discuss the overdense environment that may be the reason behind the circular shape of ORC candidates.

The RAD@home RGB-maker Tool is a python-based web application that enables citizen science research through collaboration using open-source technology. The tool fetches FITS image data from NASA SkyView and generates false colour images in Red-Green-Blue channels with contour. This helps in the basic multi-wavelength understanding and characterization of extragalactic objects, and further analysis along with reporting of potential new discoveries in a uniform format. Students from Universities or science-graduate citizens gain skills in RGB-C image analysis and identify unique features in objects via either one-day online-weekend events or week-long in-person training. Trained citizen scientists in turn are part of rare discoveries such as the jet-galaxy interaction system RAD12. The tool has been successfully used by thousands of citizen scientists in India since its launch on 26th January 2021 and has demonstrated the potential during IAU symposium 375 to be part of citizen science efforts with international participants.

Unlike most web-based citizen science programmes, RAD@home citizen scientists are trained in an interactive manner, both online and in person. This Collaboratory model can alleviate various geo-political and socio-economic constraints on the growth of people in underdeveloped regions which is in synergy with mandates of the IAU Office of Astronomy for Development. Owing to its Inter-University collaboratory design, supported by over 30 research institutions, it can attempt to convert the ‘Big Data Problem’ into a ‘Big Data Prospect’ by direct training and involving citizens in discoveries from multi-telescope data. Using the RAD-RGB-maker web-tool, e-astronomers learn the basics of multi-wavelength (UV-optical-IR-radio) extragalactic astronomy and create preliminary discovery reports of unusual radio sources thus becoming Co-Investigator in follow-up observations and publications (e.g. Discovery of RAD12). International expansion of RAD@home has been initiated during the recent IAU symposium 375 through its Educational and Outreach programme.

Understanding the nucleosynthetic origin of nitrogen and the evolution of the N/O ratio in the interstellar medium is crucial for a comprehensive picture of galaxy chemical evolution at high-redshift because most observational metallicity (O/H) estimates are implicitly dependent on the N/O ratio. The observed N/O at high-redshift shows an overall constancy with O/H, albeit with a large scatter. We show that these heretofore unexplained features can be explained by the pre-supernova wind yields from rotating massive stars (M≳10M⊙,ν/νcrit≳0.4). Our models naturally produce the observed N/O plateau, as well as the scatter at low O/H. We find the scatter to arise from varying star formation efficiency. However, the models that have supernovae dominated yields produce a poor fit to the observed N/O at low O/H. This peculiar abundance pattern at low O/H suggests that dwarf galaxies are most likely to be devoid of SNe yields and are primarily enriched by pre-supernova wind abundances.

In the present work, we have developed a two-dimensional gravitational model of barred galaxies to analyse the fate of escaping stars from the central barred region. For that, the model has been analysed for two different bar profiles viz. strong and weak. Here the phenomena of stellar escape from the central barred region have been studied from the perspective of an open Hamiltonian dynamical system. We observed that the escape routes correspond to the escape basins of the two index-1 saddle points. Our results show that the formation of spiral arms is encouraged for the strong bars. Also, the formation of grand design spirals is more likely for strong bars if they host central super massive black holes (SMBHs). In the absence of central SMBHs, the formation of less-prominent spiral arms is more likely. Again, for weak bars, the formation of inner disc rings is more probable.

Thanks to deep optical to near-IR imaging and spectroscopy, significant progress is made in characterizing the rest-frame UV to optical properties of galaxies in the early universe (z > 4. Surveys with Hubble, Spitzer, and ground-based facilities (Keck, Subaru, and VLT) provide spectroscopic and photometric redshifts, measurements of the spatial structure, stellar masses, and optical emission lines for large samples of galaxies. Recently, the Atacama Large (Sub) Millimeter Array (ALMA) has become a major player in pushing studies of high redshift galaxies to far-infrared wavelengths, hence making panchromatic surveys over many orders of frequencies possible. While past studies focused mostly on bright sub-millimeter galaxies, the sensitivity of ALMA now enables surveys like ALPINE, which focuses on measuring the gas and dust properties of a large sample of normal main-sequence galaxies at z > 4. Combining observations across different wavelengths into a single, panchromatic picture of galaxy formation and evolution is currently and in the future an important focus of the astronomical community.

The Bulge Asymmetries and Dynamical Evolution (BAaDE) survey aims to explore the complex structure of the inner Galaxy and Galactic Bulge, by using the 43 GHz receivers at the Karl G. Jansky Very Large Array (VLA) and the 86 GHz receivers at the Atacama Large Millimeter/submillimeter Array (ALMA) to observe SiO maser lines in red giant stars. The goal is to construct a sample of stellar point-mass probes that can be used to test models of the gravitational potential, and the final sample is expected to provide at least 20,000 line-of-sight velocities and positions. A possible bias between the VLA and the ALMA SiO maser lines is explored, and the 86 GHz SiO line-peak velocities agree using either of the four sampled lines. Additionally, the SiO maser velocities agree with the OH maser derived velocities.

Here, we explore the enrichment of Lithium in the Galaxy using a large sample of stars common among large spectroscopic surveys such as the GALAH and astrometric survey by the Gaia satellite. For this study we used about 60,000 low mass (M⩽ 2M⊙) dwarfs from the GALAH survey. Further, we discuss Li enrichment among giant stars based on a sample of 52,000 low mass giants, of which 335 are Li-rich with A(Li) ⩾ 1.80 ± 0.14 dex, culled from the GALAH survey. These low mass giants appears to be one of the promising source of Li enrichment in the Galaxy as their atmospheric Li can be added to the ISM through mass loss.

We leverage new ultra-deep, high resolution, multi-frequency radio imaging at 6 and 3 GHz with the unique datasets available in the GOODS-S/HUDF region in order to assess the AGN fraction in a faint radio-selected sample. For AGN identification, we adopt a multi-wavelength approach, combining X-ray and (mid-)infrared (IR) selections with radio identification such as X-ray to radio excess, flat radio spectral slopes, and the radio-IR correlation. We identify AGN in 43% of our radio sample, yielding an AGN source density of ∼ 1 arcmin−2. This AGN fraction is likely underestimated, as 1) our shallower 3 GHz data is biased against flat radio spectrum sources and 2) all of our selections may be biased against the most heavily obscured AGN. The James Webb Space Telescope’s Mid-Infrared Instrument (MIRI) will address the latter issue and we briefly outline our Cycle 1 Guaranteed Time Observation (GTO) program to search for heavily obscured AGN.