arXiv subjects

Cristobal Bordiu

Publications and source records attributed to Cristobal Bordiu.

13 recordsLinked to original sources

arXiv2026

SMGPS: A study of Galactic HII regions with extended morphology

We present a study of ionised hydrogen ($\textrm{H}\scriptstyle\mathrm{II}$) regions in the Galactic Plane using data from the SARAO MeerKAT Galactic Plane Survey (SMGPS). The SMPGS is a wide-field, wide-band 1.3 GHz radio continuum survey ($251^\circ \leq l \leq 358^\circ$ and $2^\circ \leq l \leq 61^\circ$ at $\quad |b| \leq 1^\circ.5$) that has enabled us to trace the diffuse emission enveloping recently formed massive stars. Our multifrequency synthesis images reveal faint and extended emission that was previously overlooked by $\textrm{H}\scriptstyle\mathrm{II}$ region surveys. We report the distances and Lyman-photon flux ($N_{\mathrm{Ly}}$) measurements for 1,327 Galactic $\textrm{H}\scriptstyle\mathrm{II}$ regions from which we characterise the spectral types for candidate ionising stars. The spectral types range from B2 to O4. The typical stellar spectral type responsible for ionisation is the B0, which constitutes about $\text{16%}$ of our catalogue, corresponding to a mean $\log(N_{\mathrm{Ly}}) = 47.5\ \mathrm{s}^{-1}$. Moreover, as a result of the lack of radio recombination line (RRL) velocity measurements for faint $\textrm{H}\scriptstyle\mathrm{II}$ regions, we identify the effective completeness limit at $\log(N_{\mathrm{Ly}}) \approx 47.6\ \mathrm{s}^{-1}$. The multiwavelength approach reveals that the physical radius at 1.3 GHz and in the mid-infrared are well correlated with a slope of $1.15 \pm 0.02$. We find clear power-law relations between $N_{\mathrm{Ly}}$ and physical radius, and an inverse correlation between electron density and radius ($n_{\rm e} \propto R^{-0.73}$). However, no significant correlation is observed between the $N_{\mathrm{Ly}}$ and Galactocentric distance, suggesting that the observed trends are governed primarily by local star-forming environments rather than large-scale Galactic gradients.

astro-ph.GA↗

arXiv2026

Determination of kinematic distances of WISE & SMGPS H II regions in the Galactic plane using SEDIGISM cloud association

One of the fundamental requirements for studying and understanding Galactic structure and massive star formation is accurate distances to H II regions. However, most distance assignments are hampered by kinematic distance ambiguity (KDA), sparse parallax measurements, and the large number of radio continuum sources lacking velocity and distance measurements. We present a kinematic distance determination method via cloud association, linking H II regions from the Wide-field Infrared Survey Explorer (WISE) catalogue and the South African Radio Astronomy Observatory (SARAO) MeerKAT Galactic Plane Survey (SMGPS) with molecular clouds from the Structure, Excitation and Dynamics of the Inner Galactic Interstellar Medium (SEDIGISM) 13CO (2-1) survey. The associations are established through spatial overlap and velocity coherence, and the molecular cloud velocity and distance are then assigned to the associated H II region. The method yields 741 H II regions with adopted CO-based systemic velocities, of which 640 have reliable kinematic distances based on the SEDIGISM distance reliability criteria. We validate the method using 329 H II regions with independent radio recombination line (RRL) velocities, finding excellent agreement with a median absolute velocity difference of 3.46km/s. Our analysis resolves ambiguous velocities for 40 H II regions with multiple WISE RRL velocity measurements. Compared to the unassociated clouds, the associated molecular clouds exhibit significantly higher masses, gas surface densities, linewidths, star formation efficiencies and dense gas fractions, and slightly lower virial parameters. This work provides a large, homogeneously-derived catalogue of H II region distances and establishes a framework for further studying massive star formation and Galactic structure in general.

astro-ph.GA↗

arXiv2026

Coherent and Incoherent Emission from the Ordered Magnetospheres of Low-Mass Stars, UCDs, and Massive Stars

Massive early-type (B/A) stars and ultracool dwarfs (UCDs) represent two distinct regimes in which ordered, large-scale magnetospheres are observed. In rapidly rotating massive stars, incoherent radio emission is explained by the centrifugal breakout (CBO) mechanism: plasma confined within the rigidly rotating magnetosphere accumulates beyond the co-rotation radius, where centrifugal forces trigger breakout events and magnetic reconnection, generating non-thermal electrons that produce incoherent gyro-synchrotron emission. Empirically, the radio luminosity correlates with the power released by CBO events, establishing a clear link between stellar rotation, magnetic confinement, and radio output. In UCDs, persistent non-thermal radio emission exhibits similar luminosity trends to those of massive magnetic stars, despite the absence of strong stellar winds. This similarity suggests that a CBO-like process may also operate in these fully convective, low-mass objects, though the plasma source and acceleration mechanisms remain uncertain. In both classes, coherent electron cyclotron maser emission (ECME), characterized by strong polarization and rotational modulation, is observed, indicating common magnetospheric processes analogous to planetary auroral emission. The Square Kilometre Array (SKA) will be able to deeply observe about 70\% of the sky. We expect to observe $\sim 1000$ UCDs, enabling better statistical analysis of their emission and a test of the CBO hypothesis.

astro-ph.SR↗

arXiv2025

The SARAO MeerKAT Galactic Plane Survey compact source catalogue

We present a catalogue of compact sources detected in the SARAO MeerKAT 1.3 GHz Galactic Plane Survey (SMGPS). We extract 510599 compact sources, with areas less than five 8" beams, from the survey maps covering the regions $252°< l < 358^°$ and $2°< l < 61°$ at $|b| \leq 1.5^°$, which have an angular resolution of 8" and a sensitivity of $\sim$ 10-30 $μ$Jy beam$^{-1}$. In this paper, we describe the source identification and characterisation methods, present the quality assurance of the catalogue, explore the nature of the catalogue sources, and present initial science highlights. We limit our catalogue to sources with a signal-to-noise ratio $\geq 5$, as the catalogue is $\sim$90 per cent complete, and has a false positive rate of less than 1 per cent at this threshold. The bulk of the catalogue sources are previously unknown to the literature, with the majority of unknown sources at sub-mJy levels. Initial science highlights from the catalogue include the detection of 213 radio quiet WISE HII region candidates, previously undetected in radio continuum studies. We show images that compare the SMGPS compact sources to CORNISH ultracompact HII regions, thus highlighting the sensitivity and unprecedented uv-coverage of the SMGPS, and the potential synergy of the SMGPS with other surveys.

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↗

arXiv2024

The SARAO MeerKAT Galactic Plane Survey filamentary source catalogue

We present a catalogue of filamentary structures identified in the SARAO (South African Radio Astronomy Observatory) MeerKAT 1.3 GHz Galactic Plane Survey (SMGPS). We extract 933 filaments across the survey area, 803 of which (~86%) are associated with extended radio structures (e.g. supernova remnants and HII regions), whilst 130 (~14%) are largely isolated. We classify filaments as thermal or non-thermal via their associated mid-infrared emission and find 77/130 (~59%) of the isolated sources are likely to be non-thermal, and are therefore excellent candidates for the first isolated, non-thermal radio filaments observed outside of the Galactic Centre (GC). Comparing the morphological properties of these non-thermal candidates to the non-thermal filaments observed towards the GC we find the GC filaments are on the whole angularly narrower and shorter than those across the SMGPS, potentially an effect of distance. The SMGPS filaments have flux densities similar to those of the GC, however the distribution of the latter extends to higher flux densities. If the SMGPS filaments were closer than the GC population, it would imply a more energetic population of cosmic ray electrons in the GC. We find the filament position angles in the SMGPS are uniformly distributed, implying that the local magnetic field traced by the filaments does not follow the large-scale Galactic field. Finally, although we have clearly shown that filaments are not unique to the GC, the GC nevertheless has the highest density of filaments in the Milky Way.

astro-ph.GA↗

arXiv2023

EMU Detection of a Large and Low Surface Brightness Galactic SNR G288.8-6.3

We present the serendipitous detection of a new Galactic Supernova Remnant (SNR), G288.8-6.3 using data from the Australian Square Kilometre Array Pathfinder (ASKAP)-Evolutionary Map of the Universe (EMU) survey. Using multi-frequency analysis, we confirm this object as an evolved Galactic SNR at high Galactic latitude with low radio surface brightness and typical SNR spectral index of $α= -0.41\pm0.12$. To determine the magnetic field strength in SNR G288.8-6.3, we present the first derivation of the equipartition formulae for SNRs with spectral indices $α>-0.5$. The angular size is $1.\!^\circ 8\times 1.\!^\circ 6$ $(107.\!^\prime 6 \times 98.\!^\prime 4)$ and we estimate that its intrinsic size is $\sim40$pc which implies a distance of $\sim1.3$kpc and a position of $\sim140$pc above the Galactic plane. This is one of the largest angular size and closest Galactic SNRs. Given its low radio surface brightness, we suggest that it is about 13000 years old.

astro-ph.HE↗

arXiv2023

RADiff: Controllable Diffusion Models for Radio Astronomical Maps Generation

Along with the nearing completion of the Square Kilometre Array (SKA), comes an increasing demand for accurate and reliable automated solutions to extract valuable information from the vast amount of data it will allow acquiring. Automated source finding is a particularly important task in this context, as it enables the detection and classification of astronomical objects. Deep-learning-based object detection and semantic segmentation models have proven to be suitable for this purpose. However, training such deep networks requires a high volume of labeled data, which is not trivial to obtain in the context of radio astronomy. Since data needs to be manually labeled by experts, this process is not scalable to large dataset sizes, limiting the possibilities of leveraging deep networks to address several tasks. In this work, we propose RADiff, a generative approach based on conditional diffusion models trained over an annotated radio dataset to generate synthetic images, containing radio sources of different morphologies, to augment existing datasets and reduce the problems caused by class imbalances. We also show that it is possible to generate fully-synthetic image-annotation pairs to automatically augment any annotated dataset. We evaluate the effectiveness of this approach by training a semantic segmentation model on a real dataset augmented in two ways: 1) using synthetic images obtained from real masks, and 2) generating images from synthetic semantic masks. We show an improvement in performance when applying augmentation, gaining up to 18% in performance when using real masks and 4% when augmenting with synthetic masks. Finally, we employ this model to generate large-scale radio maps with the objective of simulating Data Challenges.

cs.CV↗

arXiv2023

Radio astronomical images object detection and segmentation: A benchmark on deep learning methods

In recent years, deep learning has been successfully applied in various scientific domains. Following these promising results and performances, it has recently also started being evaluated in the domain of radio astronomy. In particular, since radio astronomy is entering the Big Data era, with the advent of the largest telescope in the world - the Square Kilometre Array (SKA), the task of automatic object detection and instance segmentation is crucial for source finding and analysis. In this work, we explore the performance of the most affirmed deep learning approaches, applied to astronomical images obtained by radio interferometric instrumentation, to solve the task of automatic source detection. This is carried out by applying models designed to accomplish two different kinds of tasks: object detection and semantic segmentation. The goal is to provide an overview of existing techniques, in terms of prediction performance and computational efficiency, to scientists in the astrophysics community who would like to employ machine learning in their research.

cs.CV↗

arXiv2023

Star-Planet Interaction at radio wavelengths in YZ Ceti: Inferring planetary magnetic field

In exoplanetary systems, the interaction between the central star and the planet can trigger Auroral Radio Emission (ARE), due to the Electron Cyclotron Maser mechanism. The high brightness temperature of this emission makes it visible at large distances, opening new opportunities to study exoplanets and to search for favourable conditions for the development of extra-terrestrial life, as magnetic fields act as a shield that protects life against external particles and influences the evolution of the planetary atmospheres. In the last few years, we started an observational campaign to observe a sample of nearby M-type stars known to host exoplanets with the aim to detect ARE. We observed YZ Ceti with the upgraded Giant Metrewave Radio Telescope (uGMRT) in band 4 (550-900 MHz) nine times over a period of five months. We detected radio emission four times, two of which with high degree of circular polarization. With statistical considerations we exclude the possibility of flares due to stellar magnetic activity. Instead, when folding the detections to the orbital phase of the closest planet YZ Cet b, they are at positions where we would expect ARE due to star-planet interaction (SPI) in sub-Alfvenic regime. With a degree of confidence higher than 4.37 sigma, YZ Cet is the first extrasolar systems with confirmed SPI at radio wavelengths. Modelling the ARE, we estimate a magnetic field for the star of about 2.4 kG and we find that the planet must have a magnetosphere. The lower limit for the polar magnetic field of the planet is 0.4 G.

astro-ph.EP↗

arXiv2023

Radio source analysis services for the SKA and precursors

New developments in data processing and visualization are being made in preparation for upcoming radioastronomical surveys planned with the Square Kilometre Array (SKA) and its precursors. A major goal is enabling extraction of science information from the data in a mostly automated way, possibly exploiting the capabilities offered by modern computing infrastructures and technologies. In this context, the integration of source analysis algorithms into data visualization tools is expected to significantly improve and speed up the cataloguing process of large area surveys. To this aim, the CIRASA (Collaborative and Integrated platform for Radio Astronomical Source Analysis) project was recently started to develop and integrate a set of services for source extraction, classification and analysis into the ViaLactea visual analytic platform and knowledge base archive. In this contribution, we will present the project objectives and tools that have been developed, interfaced and deployed so far on the prototype European Open Science Cloud (EOSC) infrastructure provided by the H2020 NEANIAS project.

astro-ph.IM↗

arXiv2021

Novel EOSC Services for Space Challenges: The NEANIAS First Outcomes

The European Open Science Cloud (EOSC) initiative faces the challenge of developing an agile, fit-for-purpose, and sustainable service-oriented platform that can address the evolving needs of scientific communities. The NEANIAS project plays an active role in the materialization of the EOSC ecosystem by actively contributing to the technological, procedural, strategic and business development of EOSC. We present the first outcomes of the NEANIAS activities relating to co-design and delivery of new innovative services for space research for data management and visualization (SPACE-VIS), map making and mosaicing (SPACE-MOS) and pattern and structure detection (SPACE-ML). We include a summary of collected user requirements driving our services and methodology for their delivery, together with service access details and pointers to future works.

astro-ph.IM↗

arXiv2020

Toward porting Astrophysics Visual Analytics Services to the European Open Science Cloud

The European Open Science Cloud (EOSC) aims to create a federated environment for hosting and processing research data to support science in all disciplines without geographical boundaries, such that data, software, methods and publications can be shared as part of an Open Science community of practice. This work presents the ongoing activities related to the implementation of visual analytics services, integrated into EOSC, towards addressing the diverse astrophysics user communities needs. These services rely on visualisation to manage the data life cycle process under FAIR principles, integrating data processing for imaging and multidimensional map creation and mosaicing, and applying machine learning techniques for detection of structures in large scale multidimensional maps.

astro-ph.IM↗