arXiv subjects

Andrew M. Hopkins

Publications and source records attributed to Andrew M. Hopkins.

At least 19 recordsLinked to original sources

arXiv2026

Bridging the mass gap: Diffuse radio emission in GAMA galaxy groups using EMU and DINGO survey data

Diffuse radio emission provides a powerful probe of non-thermal processes in the large-scale structure, yet its properties in galaxy groups remain poorly constrained. Using deep 943 MHz radio continuum data from the Evolutionary Map of the Universe (EMU) and 1.37 GHz data from the Deep Investigations of Neutral Gas Origins (DINGO) survey, we investigate diffuse radio emission in 400 galaxy groups selected from the GAMA survey at $z < 0.1$. We employ a multi-resolution filtering technique to suppress compact radio sources and enhance extended, low-surface-brightness emission associated with the intra group medium. Integrated flux densities are measured within group radii, and background fluctuations are quantified using random control regions. While most systems yield non-detections, we identify 46/400 galaxy groups with candidate diffuse emission, spanning radio powers of $10^{19}-10^{24}\,\mathrm{W\,Hz^{-1}}$. Stacked measurements reveal a weak positive trend between radio power and halo mass. The observed emission levels lie above simple extrapolations of cluster scaling relations, suggesting that different physical processes dominate in the group regime. Additionally, stellar mass ratios of the most massive galaxies in the group and Early Type Galaxy fractions suggest that these galaxy groups are relatively young, evolving systems where galaxy interactions and mergers may power the emission. Comparisons with Magneto Hydrodynamical simulations indicate shock acceleration alone cannot explain the observed emission, pointing to an important role for fossil plasma re-acceleration and group-scale dynamical activity. These results demonstrate diffuse radio emission is present in a non-negligible fraction of galaxy groups, providing new constraints on non-thermal processes in low-mass environments.

astro-ph.GA↗

arXiv2026

EMU: Cross-correlating EMU Pilot Survey 1 with Dark Energy Survey to validate the radio galaxy bias and redshift distribution

Radio continuum galaxy surveys can provide a relatively fast map of the projected distribution of structure in the Universe, at the cost of lacking information about the radial distribution. We can use these surveys to learn about the growth of structure and the fundamental physics of the Universe, but doing so requires extra information to be provided in the modelling of the redshift distribution, $dN/dz$. In this work, we show how the cross-correlation of the two-dimensional radio continuum map with another galaxy map (in this case a photometric optical extragalactic survey), with a known redshift distribution, can be used to determine the redshift distribution through statistical inference. We use data from the Evolutionary Map of the Universe (EMU) Pilot Survey 1 and cross-correlate it with optical data from the Dark Energy Survey to fit the parameters of our $dN/dz$ model. We show that the recovered distribution has a similar shape to the distribution predicted by the current state-of-the-art simulation, and can fit the angular power spectrum data from cross-correlations very well, validating this model. These results will have significance for future cosmological analyses with large-scale radio continuum surveys such as the full EMU, or with the SKAO.

astro-ph.CO↗

arXiv2026

Extended Radio Galaxies in EMU: A Comparative Look at Source-Finding Techniques

Extended radio sources present unique challenges for automated detection and classification in wide-field radio surveys. With current surveys such as the Evolutionary Map of the Universe (EMU), robust and scalable methods are essential to identify and catalogue these complex sources. We apply three automatic approaches to detect complex radio emission in EMU observations of the Galaxy And Mass Assembly (GAMA) 09 field (EMU-G09) in order to evaluate their relative strengths and limitations in preparation for large-scale application across future EMU data releases. These include DRAGNHunter, designed to detect likely DRAGNs (Double Radio sources associated with Active Galactic Nuclei) from a component catalogue; coarse-grained complexity, a metric designed to highlight regions of complex emission; and RG-CAT, a machine learning pipeline trained on radio sources identified in the EMU pilot survey. We find that together, the three methods recover nearly all extended sources in EMU-G09 but identify largely distinct, partially-overlapping subsets, with only 375 sources identified by all finders. This demonstrates that a combination of complementary techniques will be required to achieve a complete census of extended radio sources in future large-scale surveys.

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arXiv2026

Radio detection of supernova remnant G310.7-5.4 with $γ$-ray counterpart: Abeona SNR

G310.7-5.4 is a supernova remnant (SNR) candidate identified as a faint shell in the second epoch Molonglo Galactic Plane Survey (MGPS-2), but this has not been followed up with multi-wavelength observations until now. It is an example of an SNR at high Galactic latitude showing spatially coinciding $γ$-ray emission. Here, we make the first detailed investigation of the radio emission from the G310.7-5.4 region, aiming to characterise the radio structure, polarisation measurements and the coinciding GeV emission. We used recent radio continuum observations at 943.5 MHz from the EMU and the POSSUM surveys with ASKAP, as well as 16.5 years of Fermi-LAT observations. We furthermore considered the multiwavelength context of the object by investigating observations previously conducted with other instruments, such as infrared and X-ray surveys. We confirm the SNR candidate as a new supernova remnant, dubbed Abeona. We detect the presence of a faint, extended, bilateral radio shell of the size of around 30' diameter and ASKAP radio flux density of $1.5^{+1.5}_{-0.1}$ Jy with no obvious infrared counterparts. With a radio surface brightness of about $2.4^{+2.4}_{-0.1}\times10^{-22}$ W m$^{-2}$ Hz$^{-1}$ sr$^{-1}$, this SNR is one of the faintest radio SNRs known. The northern part of the shell shows linearly polarised radio emission, characteristic of synchrotron emission in SNRs. The physical size of the SNR is estimated to be around $42^{+42}_{-21}$ pc, which would give a distance of around $4.9^{+4.9}_{-2.5}$ kpc. Furthermore, the spatially coincident $γ$-ray source 4FGL J1413.9-6705 shows an energy flux of $1.26\pm0.35\times 10^{-6}$ MeV cm$^{-2}$ s$^{-1}$ with a significance of 5.7 $σ$ between 100 MeV and 100 GeV. The SNR is also put in context with known high-latitude SNRs with $γ$-ray counterparts and compared with their observational properties.

astro-ph.HE↗

arXiv2026

The Salamander: A case study of the magnetic field and peculiar morphology of G309.8-2.6 through radio polarimetry

Studying the interaction between core-collapse supernova remnants (SNRs) and their surrounding environments is essential to understanding the mechanism for energy transfer to the interstellar medium (ISM) and the intrinsic physical properties of these remnants. In this paper, we focus on G309.8-2.6. Our new observations reveal that this object includes an SNR shell with a relic pulsar wind nebula (PWN) that extends well beyond the emission that has been previously observed in X-rays. We present new radio continuum and polarization images of G309.8-2.6 from the Evolutionary Map of the Universe (EMU) and Polarization Sky Survey of the Universe's Magnetism (POSSUM) surveys with the Australian Square Kilometre Array Pathfinder (ASKAP). The images reveal the complex and peculiar morphology of G309.8-2.6. The linear polarization displays an atypical S-shaped morphology and a highly ordered magnetic field. The rotation measure (RM) map shows a large-scale gradient or possible sign reversal, depending on the foreground RM. We reprocessed archival X-ray observations from Chandra and eROSITA, and retrieved archival H$α$ and infrared observations. We performed a joint analysis of the multiwavelength data and proposed scenarios to explain the unusual shape. Our results place new constraints on the magnetic field of G309.8-2.6, including its environment, and demonstrate the power of polarization observations in probing the properties of SNRs.

astro-ph.GA↗

arXiv2026

The life of central radio galaxies in clusters: AGN-ICM studies of eRASS1 clusters in the ASKAP fields

The mechanical feedback from the central AGNs can be crucial for balancing the radiative cooling of the intracluster medium at the cluster centre. We aim to understand the relationship between the power of AGN feedback and the cooling of gas in the centres of galaxy clusters by correlating the radio properties of the brightest cluster galaxies (BCGs) with the X-ray properties of their host clusters. We used catalogues from the first SRG/eROSITA All-Sky Survey (eRASS1) along with ASKAP radio data. In total, we identified 134 radio sources associated with BCGs of the 151 eRASS1 clusters located in the PS1, PS2, and SWAG-X ASKAP fields. Non-detections were treated as upper limits. We correlated BCG radio luminosity, largest linear size (LLS), and BCG offset with the integrated X-ray luminosity of their host clusters. To characterise cool cores (CCs) and non-cool cores (NCCs), we used the concentration parameter $c_{R_{500}}$ and combined it with the BCG offset to assess cluster dynamical state. We analysed the correlation between radio mechanical power and X-ray luminosity within the CC subsample. We observe a potential positive trend between LLS and BCG offset, suggesting an environmental effect on radio-source morphology. We find a weak trend where more luminous central radio galaxies are found in clusters with higher X-ray luminosity. Within the CC subsample, there is a positive but highly scattered relationship between the mechanical luminosity of AGN jets and the X-ray cooling luminosity. This finding is supported by bootstrap resampling and flux-flux analyses. The correlation indicates that AGN feedback is ineffective in high-luminosity (high-mass) clusters. At a cooling luminosity of $L_{\mathrm{X},~r<R_\mathrm{cool}}\approx 5.50\times10^{43}$ erg/s, on average, AGN feedback appears to contribute only about 13%-22% of the energy needed to offset the radiative losses in the ICM.

astro-ph.CO↗

arXiv2026

The Secret Lives of Open Clusters: a Multiwavelength Examination of Three Open Clusters

Star clusters are well known for their dynamical interactions, an outcome of their high stellar densities; in this paper we use multiwavelength observations to search for the unique outcomes of these interactions in three nearby Galactic open clusters: IC 2602 (30 Myr), NGC 2632 (750 Myr) and M67 (4 Gyr). We compared X-ray observations from all-sky surveys like eROSITA, plus archival observations from Chandra X-ray Observatory, survey radio observations from ASKAP's Evolutionary Map of the Universe survey plus archival VLA observations, in conjunction with new cluster catalogs with Gaia. From X-ray, we found 77 X-ray sources likely associated with IC 2602, 31 X-ray sources in NGC 2632, and 31 near M67's central regions. We were further able to classify these X-ray sources based on their optical variability and any radio emission. Three IC 2602 X-ray sources had radio counterparts, which are likely all chromospherically active binary stars. We also identified luminous radio and X-ray variability from a spectroscopic triple system in M67, WOCS 3012/S1077, which is either consistent with a quiescent black hole binary, or due to an active binary stellar system. A recent population study of optical variables by Anderson & Hunt 2025 shows that the population of optical variables in open clusters clearly changes over cluster age; this pilot study gives evidence that the X-ray population also changes with time, and demonstrates the need for a broader multiwavelength study of Galactic open clusters.

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arXiv2025

Galaxy and Mass Assembly (GAMA): The Properties of Quasar Host Galaxies: Star Formation Histories and Stellar Populations

We investigated the star formation history and stellar populations of a sample of 205 Type I quasar host galaxies (0.1$<$z$<$0.35) and compared with normal (non-active) galaxies of the same mass and redshift within the volume of the Galaxy and Mass Assembly (GAMA) redshift survey. We find that quasar host galaxies tend to be star-forming galaxies ($\sim$ 80%) lying on the star-forming MS; the fraction of quasar host galaxies that are quiescent ($\sim$ 20%) is lower than the fraction of quiescent galaxies in the comparison sample of normal galaxies (54%). We find that the mean star formation rate of quasar host galaxies has increased over the past 100 Myr by a factor of 2--3, but these galaxies were star-forming at all times previously. Our data are more consistent with quasar activity originating together with an increase in the star formation rate of otherwise normal galaxies, similar to episodic star formation in normal spirals. We argue that this indicates that secular processes and minor mergers may be the favored triggers of nuclear activity in the local Universe.

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arXiv2025

Radio Galaxy Zoo EMU: Harnessing Citizen Science and AI to Advance Open Science Catalogues

Over the past decades, significant efforts have been devoted to developing sophisticated algorithms for automatically identifying and classifying radio sources in large surveys. However, even the most advanced methods face challenges in recognising complex radio structures and accurately associating radio emission with their host galaxies. Leveraging data from the ASKAP telescope and the Evolutionary Map of the Universe (EMU) survey, Radio Galaxy Zoo EMU (RGZ EMU) was created to generate high-quality radio source classifications for training deep learning models and cataloging millions of radio sources in the southern sky. By integrating novel machine learning techniques, including anomaly detection and natural language processing, our workflow actively engages citizen scientists to enhance classification accuracy. We present results from Phase I of the project and discuss how these data will contribute to improving open science catalogues like EMUCAT.

astro-ph.GA↗

arXiv2025

EMU and the DRAGNs I: A Catalogue of DRAGNs

We present a catalogue of 3557 Double Radio sources associated with Active Galactic Nuclei (DRAGNs) from the First Pilot Survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, covering 270 deg^2. We have extracted and identified each source by eye, tagged it with a morphological type and measured its parameters. The resulting catalogue will be used in subsequent papers to explore the properties of these sources, to train machine-learning algorithms for the detection of these sources in larger fields, and to compare with the results of Citizen Science projects, with the ultimate goal of understanding the physical processes that drive DRAGNs. Compared with earlier, lower sensitivity, catalogues, we find more diffuse structure and a plethora of more complex structures, ranging from wings of radio emission on the side of the jets, to types of object which have not been seen in earlier observations. As well as the well-known FR1 and FR2 sources, we find significant numbers of rare types of radio source such as Hybrid Morphology Radio Sources and one-sided jets, as well as a wide range of bent-tail and head-tail sources.

astro-ph.GA↗

arXiv2025

Quantifying Radio Source Morphology

The advent of next-generation telescope facilities brings with it an unprecedented amount of data, and the demand for effective tools to process and classify this information has become increasingly important. This work proposes a novel approach to quantify the radio galaxy morphology, through the development of a series of algorithmic metrics that can quantitatively describe the structure of radio source, and can be applied to radio images in an automatic way. These metrics are intuitive in nature and are inspired by the intrinsic structural differences observed between the existing Fanaroff-Riley (FR) morphology types. The metrics are defined in categories of asymmetry, blurriness, concentration, disorder, and elongation ($ABCDE$/single-lobe metrics), as well as the asymmetry and angle between lobes (source metrics). We apply these metrics to a sample of $480$ sources from the Evolutionary Map of the Universe Pilot Survey (EMU-PS) and $72$ well resolved extensively studied sources from An Atlas of DRAGNs, a subset of the revised Third Cambridge Catalogue of Radio Sources (3CRR). We find that these metrics are relatively robust to resolution changes, independent of each other, and measure fundamentally different structural components of radio galaxy lobes. These metrics work particularly well for sources with reasonable signal-to-noise and well separated lobes. We also find that we can recover the original FR classification using probabilistic combinations of our metrics, highlighting the usefulness of our approach for future large data sets from radio sky surveys.

astro-ph.GA↗

arXiv2025

EMUSE: Evolutionary Map of the Universe Search Engine

We present EMUSE (Evolutionary Map of the Universe Search Engine), a tool designed for searching specific radio sources within the extensive datasets of the EMU (Evolutionary Map of the Universe) survey, with potential applications to other Big Data challenges in astronomy. Built on a multimodal approach to radio source classification and retrieval, EMUSE fine-tunes the OpenCLIP model on curated radio galaxy datasets. Leveraging the power of foundation models, our work integrates visual and textual embeddings to enable efficient and flexible searches within large radio astronomical datasets. We fine-tune OpenCLIP using a dataset of 2,900 radio galaxies, encompassing various morphological classes, including FR-I, FR-II, FR-x, R-type, and other rare and peculiar sources. The model is optimized using adapter-based fine-tuning, ensuring computational efficiency while capturing the unique characteristics of radio sources. The fine-tuned model is then deployed in EMUSE, allowing for seamless image- and text-based queries over the EMU survey dataset. Our results demonstrate the model's effectiveness in retrieving and classifying radio sources, particularly in recognizing distinct morphological features. However, challenges remain in identifying rare or previously unseen radio sources, highlighting the need for expanded datasets and continuous refinement. This study showcases the potential of multimodal machine learning in radio astronomy, paving the way for more scalable and accurate search tools in the field. The search engine is accessible at https://askap-emuse.streamlit.app/ and can be used locally by cloning the repository at https://github.com/Nikhel1/EMUSE.

astro-ph.GA↗

arXiv2025

Discovery of Odd Radio Circles and Other Peculiars in the First Year of the EMU Survey using Object Detection

We present a systematic search for Odd Radio Circles (ORCs) and other unusual radio morphologies using data from the first year of the EMU (Evolutionary Map of the Universe) survey. ORCs are rare, enigmatic objects characterized by edge-brightened rings of radio emission, often found in association with distant galaxies. To identify these objects, we employ a hybrid methodology combining supervised object detection techniques and visual inspection of radio source candidates. This approach leads to the discovery of five new ORCs and two additional candidate ORCs, expanding the known population of these objects. In addition to ORCs, we also identify 55 Galaxies with Large-scale Ambient Radio Emission (GLAREs), which feature irregular, rectangular, or circular shapes of diffuse radio emission mostly surrounding central host galaxies. These GLAREs may represent different evolutionary stages of ORCs, and studying them could offer valuable insights into their evolutionary processes. We also highlight a subset of Starburst Radio Ring Galaxies (SRRGs), which are star-forming galaxies exhibiting edge-brightened radio rings surrounding their central star-forming regions. We emphasize the importance of multi-wavelength follow-up observations to better understand the physical properties, host galaxy characteristics, and evolutionary pathways of these radio sources.

astro-ph.GA↗

arXiv2025

Decomposing Infrared Luminosity Functions into Star-Forming and AGN Components using CIGALE

This study presents a comprehensive analysis of the infrared (IR) luminosity functions (LF) of star-forming (SF) galaxies and active galactic nuclei (AGN) using data from the ZFOURGE survey. We employ CIGALE to decompose the spectral energy distribution (SED) of galaxies into SF and AGN components to investigate the co-evolution of these processes at higher redshifts and fainter luminosities. Our CIGALE-derived SF and AGN LFs are generally consistent with previous studies, with an enhancement at the faint end of the AGN LFs. We attribute this to CIGALE's capability to recover low-luminosity AGN more accurately, which may be underrepresented in other works. We find evidence for a significant evolutionary epoch for AGN activity below $z \approx 2$, comparable to the peak of cosmic star formation at $z \approx 2$, which we also recover well. Based on our results, the gas supply in the early universe favoured the formation of brighter star-forming galaxies from high-redshift until $z=2$, below which the gas for SF becomes increasingly exhausted. In contrast, AGN activity peaked earlier and declined more gradually, suggesting a possible feedback scenario in which AGN positively influence SF.

astro-ph.GA↗

arXiv2025

Teleios (G305.4-2.2) -- the mystery of a perfectly shaped new Galactic supernova remnant

We present the serendipitous radio-continuum discovery of a likely Galactic supernova remnant (SNR) G305.4-2.2. This object displays a remarkable circular symmetry in shape, making it one of the most circular Galactic SNRs known. Nicknamed Teleios due to its symmetry, it was detected in the new Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) radio-continuum images with an angular size of 1320"x1260" and PA = 0 deg. While there is a hint of possible H$α$ and gamma-ray emission, Teleios is exclusively seen at radio-continuum frequencies. Interestingly, Teleios is not only almost perfectly symmetric, but it also has one of the lowest surface brightnesses discovered among Galactic SNRs and a steep spectral index of $α=-0.6\pm 0.3$. Our estimates from HI studies and the Sigma-D relation place Teleios as a type Ia SNR at a distance of either ~2.2 kpc of ~7.7 kpc. This indicates two possible scenarios, either a young (under 1000 yr) or an older SNR (over 10000 yr). With a corresponding diameter of 14/48 pc, our evolutionary studies place Teleios at the either early or late Sedov phase, depending on the distance estimate. However, our modelling also predicts X-ray emission, which we do not see in the present generation of eROSITA images. We also explored a type Iax explosion scenario that points to a much closer distance of <1 kpc and Teleios size of only ~3.3 pc, which would be similar to the only known type Iax remnant SN1181. Unfortunately, all examined scenarios have their challenges, and no definitive supernova (SN) origin type can be established at this stage. Teleios's symmetrical shape suggests expansion into a rarefied and isotropic ambient medium. The low radio surface brightness and the lack of pronounced polarisation can be explained by a high level of ambient rotation measure (RM), with the largest RM being observed at centre.

astro-ph.HE↗

arXiv2025

FUV to FIR SED modelling of NGC 205

New far ultraviolet imaging of the galaxy NGC 205 is presented, which shows the emission is significantly offset ($\sim5^{\prime\prime}$ NW) from the optical and infrared centers of the galaxy. Spectral energy distribution (SED) modelling is applied to investigate the spatial dependence of the star formation history (SFH) of NGC 205, using data from far ultraviolet to far infrared. The SED model includes young and old stellar populations, gas emission, dust emission and dust absorption. The old stellar population has a total mass of $1.1\times10^8$ M$_{\odot}$ whereas the young population has a much smaller total mass of 3200 M$_{\odot}$. The best forms of SFH for old and young stars are found to be exponentially declining bursts with start times $t_0$ yr ago and e-folding times $τ$ yr. The old stellar population has uniform $t_0$=9.5 Gyr, with $τ$ decreasing with radius from 1 Gyr to 500 Myr. The young stellar population has $t_0$=900 Myr and $τ$=800 Myr, both uniform across NGC 205. The young and old stellar mass surface densities are exponential in radius with scale lengths of 40 and 110 pc, respectively. The dust heating has a $\sim$40\% contribution from young stars and $\sim$60\% from old stars.

astro-ph.GA↗

arXiv2025

ASKAP observations of the radio shell in the composite supernova remnant G310.6-1.6

We report the observations of the radio shell of the supernova remnant (SNR) G310.6-1.6 at 943 MHz from the Evolutionary Map of the Universe (EMU) and the Polarization Sky Survey of the Universe's Magnetism (POSSUM) surveys by using the Australian Square Kilometre Array Pathfinder (ASKAP). We detect polarized emission from the central pulsar wind nebula (PWN) with rotation measures varying from -696 rad m$^{-2}$ to -601 rad m$^{-2}$. We measure the integrated flux density of the shell to be 36.4 +/- 2.2 mJy at 943 MHz and derive a spectral index of -0.4 +/- 0.1 for the PWN and -0.7 +/- 0.3 for the SNR shell. From the combined radio and X-ray observations, the object can be identified as a supernova explosion of about 2500 yr ago with energy of about 1.3 x 10$^{50}$ erg, suggesting an ejected mass of about 10 M_sun. The circular radio shell outside the circular hard X-ray shell is unique among Galactic SNRs. We discuss several possible scenarios, including blast wave, reverse shock, and pulsar-fed emission, but find that none of them can fully explain the observed characteristics of the shell. This poses a challenge for understanding the evolution of SNRs. The results of this paper demonstrate the potential of the ASKAP EMU and POSSUM surveys in discovering more objects of small angular size and low surface brightness.

astro-ph.GA↗

arXiv2024

Self-supervised learning for radio-astronomy source classification: a benchmark

The upcoming Square Kilometer Array (SKA) telescope marks a significant step forward in radio astronomy, presenting new opportunities and challenges for data analysis. Traditional visual models pretrained on optical photography images may not perform optimally on radio interferometry images, which have distinct visual characteristics. Self-Supervised Learning (SSL) offers a promising approach to address this issue, leveraging the abundant unlabeled data in radio astronomy to train neural networks that learn useful representations from radio images. This study explores the application of SSL to radio astronomy, comparing the performance of SSL-trained models with that of traditional models pretrained on natural images, evaluating the importance of data curation for SSL, and assessing the potential benefits of self-supervision to different domain-specific radio astronomy datasets. Our results indicate that, SSL-trained models achieve significant improvements over the baseline in several downstream tasks, especially in the linear evaluation setting; when the entire backbone is fine-tuned, the benefits of SSL are less evident but still outperform pretraining. These findings suggest that SSL can play a valuable role in efficiently enhancing the analysis of radio astronomical data. The trained models and code is available at: \url{https://github.com/dr4thmos/solo-learn-radio}

astro-ph.IM↗