arXiv subjects

E. O'Sullivan

Publications and source records attributed to E. O'Sullivan.

At least 19 recordsLinked to original sources

arXiv2026

A radio continuum view of Stephan's Quintet: age, dynamics and origin of the shock

We present a detailed, multi-band radio continuum study of the compact galaxy group Stephan's Quintet (HCG 92). We use a combination of new (MeerKAT, uGMRT) and archival (LOFAR, VLA) observations covering the $\rm 120\,MHz{-}8\,GHz$ frequency range to examine the radio properties of the group, focusing on the famous radio ridge and surrounding diffuse emission. We find filamentary substructure and branching in the southern half of the ridge, confirm an extension of the ridge to the northwest, and identify for the first time a radio counterpart to the gas bridge linking the ridge and NGC 7319. The northern ridge, northwest extension and diffuse emission have relatively steep, curved spectra, with a high-frequency spectral index gradient running north-south along the ridge. We show that the ridge emission primarily arises from a single physical mechanism, probably strong ($\mathcal{M}\simeq 40-100$) shocks in cold gas, caused by the $\rm \sim850-1000\,kms^{-1}$ collision between NGC 7318B and tidal gas filaments produced by past galaxy interactions. Synchrotron spectral age estimates suggest the collision began at the north end of the ridge $\rm \sim20\,Myr$ ago, and finished only $\rm \sim5-6\,Myr$ ago in the south, with the southern end of the shocked ridge likely still within or close to the disk of NGC 7318B. Based on this age gradient, we find that the angle between the intruder galaxy's motion and the tidal filaments was probably only about 15 degrees, and combining this with the lack of a spectral index gradient in the diffuse radio emission suggests that NGC 7318B's direction of motion is probably close to the line of sight.

astro-ph.GA↗

arXiv2026

The Treble Clef radio phoenix and its old nonthermal filaments

By inspecting data from the LOFAR Two-meter Sky Survey (LoTSS), we noticed a peculiar bright and filamentary radio source at low-galactic latitude ($b \approx 0.5 °$). This source, detected also in previous radio observations, was originally believed to be a pulsar until Green et al. (2004) suggested that it is located in a heavily obscured galaxy cluster behind the Galactic plane. In this paper, we characterize for the first time the main properties of the host cluster (redshift, mass, temperature, X-ray luminosity, and dynamical status) by using X-ray observations performed with Chandra and SRG/eROSITA. In addition, by combining new uGMRT follow-up data with observations from the e LOFAR LBA Sky Survey (LoLSS), we perform a multifrequency, spatially resolved spectral analysis of the filamentary radio source (VLSS J0318.9+5755, nicknamed here the "Treble Clef" due to its morphology). We conclude that this source is a radio phoenix belonging to a massive, merging galaxy cluster in the Zone of Avoidance. We speculate that its complex morphology is shaped by gas motions generated in the intracluster medium during the ongoing merger, which are also likely responsible for the generation of the candidate radio halo tentatively observed in the cluster center. Owing to its highly filamentary morphology, brightness at $\lesssim$1 GHz, and extremely steep spectrum, reaching values of $α> 4$ between 400 and 650 MHz, this source represents an ideal target for high-resolution, very-low-frequency follow-up observations with LOFAR2.0.

astro-ph.CO↗

arXiv2026

The impact of strong feedback on galaxy group scaling relations

Feedback from active supermassive black holes alters the distribution of matter in the Universe by injecting energy in the neighbouring hot gaseous medium, which leads to ejection of gas from the halos of galaxy groups and massive galaxies. Recent cosmological simulations such as FLAMINGO calibrate their feedback model on the baryon fractions of galaxy groups to tune the efficiency of gas ejection. However, recent observational constraints from optically selected groups and the kinetic Sunyaev-Zel'dovich effect yield lower baryon fractions than previous studies, which indicates that feedback may be more ejective than previously thought. Here we show that models involving highly ejective feedback are inconsistent with the scaling relations of local galaxy groups in the mass range $10^{13}-10^{14}M_\odot$. We study the X-ray luminosity-temperature relation in a sample of 44 galaxy groups with high-quality XMM-Newton observations. We show that highly ejective models under-predict the luminosity of galaxy groups at fixed mass at high significance ($5.7σ$). This conclusion is robust against selection effects and is obtained from directly measurable and minimally correlated quantities. We point out that turning observable quantities into gas fraction estimates is challenging, especially in the context of stacking large samples of heterogeneous systems. We argue that calibrating feedback models on baryon fractions is prone to systematic uncertainties and that observable scaling relations are better suited for this task.

astro-ph.CO↗

arXiv2026

Bound or blown: the fate of hot gas in galaxy groups

The impact of AGN feedback on the hot gas content of galaxy groups remains a key uncertainty in galaxy formation and its connection to the large scale structure of the Universe. We aim to compare the XMM-Newton Group AGN Project (X-GAP) sample to the hydrodynamical FLAMINGO simulations, which span a wide range of AGN feedback prescriptions. We construct X-GAP analogues by forward-modelling the full selection function, including detection and observational systematics, and generate end-to-end XMM-Newton mock observations analysed consistently with the data. We study multiple observables, including the L--T and Mgas--T relations, number of groups, mean temperature, and velocity dispersion, accounting for their covariance. The forward model accurately recovers input luminosities, gas masses, and core-excised temperatures for regular systems, enabling direct comparison in observable space. The normalisation of the scaling relations is the best discriminator between feedback models, while cosmic variance introduces > 20% fluctuations in the number of detected systems, making counts alone a weak discriminator. Models with intermediate feedback strength provide the best agreement with X-GAP, with the fgas-2sigma model yielding the lowest tension of only 0.8sigma, while the most extreme feedback scenario (fgas-8sigma) is ruled out at > 4sigma. Our results indicate that the thermodynamic properties of galaxy groups favour feedback stronger than the fiducial FLAMINGO calibration, but disfavour the most ejective models. This highlights the importance of combining forward modelling and multi-observable constraints to probe the fate of hot baryons in low-mass haloes.

astro-ph.CO↗

arXiv2026

A MeerKAT view of the Neutral Atomic Gas in Stephan's Quintet

We present new MeerKAT 21cm spectral line observations of the neutral hydrogen gas in the compact galaxy group Stephan's Quintet (HCG 92). These data provide a significantly improved view of the atomic gas distribution and kinematics in the group. New features include the first detections of HI associated with member galaxies NGC 7319 and NGC 7320C, the identification of an additional high-velocity HI component associated with SQ-A, and the detection of additional HI at low velocities filling much of the area of the NGC~7318B disk. We also find HI in the previously detected gas bridge linking NGC 7319 and NGC 7318B, and a new northern bridge linking NGC 7319 to the SQ-A star-formation region. We detect HI with a wide range of velocities along the line of sight through the northern half of the famous shock ridge, including in the 6200-6500$\rm\,km\,s^{-1}$ velocity range occupied by shocked H$α$ emission. We examine the morphology and velocity structure of the HI and consider the origins of different components, finding some evidence that while the gas associated with NGC 7318B has been disturbed by its collision with the group, it may still retain a component of disk rotation. We find no gaseous connection between the tidal tails and NGC 7320C, but reaffirm the close connection between the shocked gas in the ridge (traced by X-ray, radio continuum and warm H$_2$ emission) and the southern tidal tail. Based on the integrated spectrum, we find a total HI mass in the group of 3.5$\pm$0.4$\times$10$^{10}\,M_{\odot}$, higher than the VLA estimate and comparable to FAST.

astro-ph.GA↗

arXiv2026

XGAP with uGMRT I: Old AGN plasma in merging galaxy groups

Galaxy groups are affected by outflows from central Active Galactic Nuclei due to the shallower gravitational potential compared to galaxy clusters. The group binding energy is comparable to the energy output from AGN, making it an important factor in mutual evolution. We present a multi-wavelength analysis of three dynamically active groups: SDSSTG8102, SDSSTG16393, and SDSSTG28674, which are part of the XMM-Newton Group AGN Project X-GAP sample, a statistically complete sample of 49 galaxy groups. We combine uGMRT 400 MHz observations with 144 MHz LOFAR and XMM-Newton observations to study the radio sources associated with the Brightest Group Galaxies (BGGs). The BGGs in SDSSTG8102 and SDSSTG16393 have extended radio emission with asymmetric distortions in their morphologies. SDSSTG28674 has a compact flat-spectrum radio source associated with the BGG and an extended lobe on one side, connected by a faint bridge detected with LOFAR. Integrated spectral indices of the three BGGs are $-0.96\pm0.09$ (SDSSTG8102), $-1.35\pm0.09$ (SDSSTG16393), and $-1.6\pm0.02$ (SDSSTG28674). X-ray images reveal elongated morphologies in all three groups, with SDSSTG28674 showing evidence of a binary merger, while thermodynamical maps highlight temperature variations. In SDSSTG8102, lobes are bent and displaced by IGrM flows, while SDSSTG16393 hosts steep-spectrum relic-like plasma coinciding with X-ray emission. SDSSTG28674, with its ultra-steep spectrum lobe and disturbed morphology, likely traces merger-driven activity, consistent with a remnant or revived radio phoenix. The spectral diversity across the systems reflects different stages of AGN fading governed by duty cycle, source age, and confinement by the hot IGrM.

astro-ph.GA↗

arXiv2025

Radial Profiles of Radio Halos in Massive Galaxy Clusters: Diffuse Giants Over 2 Mpc

We present new, high frequency radio observations of the merging galaxy clusters PLCK G287.0+32.9, Abell 2744, and Bullet. These clusters are known to host $\sim$Mpc scale sources, known as radio halos, which are formed by the acceleration of cosmic rays by turbulence injected into the intracluster medium during cluster mergers. Our new images reveal previously undetected faint outermost regions of halos, extending to over 2 Mpc. This discovery highlights the presence of radio halos with large extents at high frequencies and suggests that their observable size depends on a combination of the observation sensitivity and uv-coverage, and their radio power. We additionally compare the properties of these three clusters with MACS J0717+3745 and Abell 2142, both of which are known to host prominent large radio halos. Remarkably, all five halos, despite their exceptionally large extents, exhibit properties similar to other classical halos: their radial profiles are described by a single-component exponential fit, they show radial spectral index steepening, and have an average radio emissivity of about $10^{-42}\, \mathrm{erg\,s^{-1}\,cm^{-3}\,Hz^{-1}}$. Our results demonstrate that radio halos can extend to the cluster periphery, without the transition to an observationally distinguishable different halo component in the outermost regions. Our findings highlight that careful subtraction of unrelated sources embedded in the halo is necessary to measure the radio surface brightness accurately, as incomplete subtraction can introduce an apparent secondary component in the peripheral regions.

astro-ph.CO↗

arXiv2025

Chandra X-ray Observatory study of the X-ray emission of PKS 0023-26 and comparison with recent ALMA results

We present a deep high-resolution Chandra X-ray Observatory image data of a powerful compact radio source PKS 0023-26 associated with a quasar at redshift 0.322. The earlier studies of the optical environment suggested that the source could be located in a galaxy cluster or a group. However, we report a non-detection of hot gas on large scales (out to $\sim 60$ kpc radius) and place an upper limit on the X-ray luminosity of $<3\times10^{42}$ erg s$^{-1}$, consistent only with the presence of a poor, low-temperature ($\rm kT < 0.5$ keV) galaxy group. X-ray spectral analysis of the central circular region, $r<7$ kpc shows, in addition to the mildly absorbed AGN, a thermal emission component with a temperature of $\rm kT=0.9^{+0.19}_{-0.37}$ keV. We discuss the origin of this hot component as a result of interaction between the evolving radio source and the interstellar medium. Our high angular resolution X-ray image traces the distribution of hot gas which is closely aligned with and extends beyond the radio source, and also in the direction perpendicular to the radio source axis. The X-rays are enhanced at the northern radio lobe and the location of the peak of the CO(3-2)/CO(2-1) line emission, suggesting that the interactions between the jet and cold medium result in the X-ray radiation which excites CO. The shock driven by the jet into the ISM is supersonic with the Mach number of $\mathcal{M} \sim 1.75-2$, creating the cocoon of hot X-rays surrounding the radio source. This result agrees with observations of shocks in other radio galaxies pointing to a prevalent impact of jets on ISM.

astro-ph.GA↗

arXiv2025

Extreme AGN feedback in the fossil galaxy group SDSSTG 4436

Supermassive black hole feedback is the currently favoured mechanism to regulate the star formation rate of galaxies and prevent the formation of ultra-massive galaxies ($M_\star>10^{12}M_\odot$). However, the mechanism through which the outflowing energy is transferred to the surrounding medium strongly varies from one galaxy evolution model to another, such that a unified model for AGN feedback does not currently exist. The hot atmospheres of galaxy groups are highly sensitive laboratories of the feedback process, as the injected black hole energy is comparable to the binding energy of halo gas particles. Here we report multi-wavelength observations of the fossil galaxy group SDSSTG 4436. The hot atmosphere of this system exhibits a highly relaxed morphology centred on the giant elliptical galaxy NGC~3298. The X-ray emission from the system features a compact core ($<$10 kpc) and a steep increase in the entropy and cooling time of the gas, with the cooling time reaching the age of the Universe $\sim15$ kpc from the centre of the galaxy. The observed entropy profile implies a total injected energy of $\sim1.5\times10^{61}$ ergs, which given the high level of relaxation could not have been injected by a recent merging event. Star formation in the central galaxy NGC~3298 is strongly quenched and its stellar population is very old ($\sim$10.6 Gyr). The currently detected radio jets have low power and are confined within the central compact core. All the available evidence implies that this system was affected by giant AGN outbursts which excessively heated the neighbouring gas and prevented the formation of a self-regulated feedback cycle. Our findings imply that AGN outbursts can be energetic enough to unbind gas particles and lead to the disruption of cool cores.

astro-ph.GA↗

arXiv2025

Modelling the selection of galaxy groups with end to end simulations

Feedback from supernovae and AGN shapes galaxy formation and evolution, yet its impact remains unclear. Galaxy groups offer a crucial probe, as their binding energy is comparable to that available from their central AGN. The XMM-Newton Group AGN Project (X-GAP) is a sample of 49 groups selected in X-ray (ROSAT) and optical (SDSS) bands, providing a benchmark for hydrodynamical simulations. In sight of such a comparison, understanding selection effects is essential. We aim to model the selection function of X-GAP by forward modelling the detection process in the X-ray and optical bands. Using the Uchuu simulation, we build a halo light cone, predict X-ray group properties with a neural network trained on hydro simulations, and assign galaxies matching observed properties. We compare the selected sample to the parent population. Our method provides a sample that matches the observed distribution of X-ray luminosity and velocity dispersion. The 50% completeness is reached at a velocity dispersion of 450 km/s in the X-GAP redshift range. The selection is driven by X-ray flux, with secondary dependence on velocity dispersion and redshift. We estimate a 93% purity level in the X-GAP parent sample. We calibrate the velocity dispersion-halo mass relation. We find a normalisation and slope in agreement with the literature, and an intrinsic scatter of about 0.06 dex. The measured velocity dispersion is accurate within 10% only for rich systems with more than about 20 members, while the velocity dispersion for groups with less than 10 members is biased at more than 20%. The X-ray follow-up refines the optical selection, enhancing purity but reducing completeness. In an SDSS-like setup, velocity dispersion measurement errors dominate over intrinsic scatter. Our selection model will enable the comparisons of thermodynamic properties and gas fractions between X-GAP groups and hydro simulations.

astro-ph.CO↗

arXiv2025

Relighting the fire in Hickson Compact Group (HCG) 15: magnetised fossil plasma revealed by the SKA Pathfinders & Precursors

In the context of the life cycle and evolution of active galactic nuclei (AGN), the environment plays an important role. In particular, the over-dense environments of galaxy groups, where dynamical interactions and bulk motions have significant impact, offer an excellent but under-explored window into the life cycles of AGN and the processes that shape the evolution of relativistic plasma. Pilot Survey observations with the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey recovered diffuse emission associated with the nearby (z = 0.0228) galaxy group HCG15, which was revealed to be strongly linearly polarised. We study the properties of this emission in unprecedented detail to settle open questions about its nature and its relation to the group-member galaxies. We perform a multi-frequency spectropolarimetric study of HCG15 incorporating our ASKAP EMU observations as well as new data from MeerKAT, LOFAR, the GMRT, and the Karl G. Jansky Very Large Array (VLA), plus X-ray data from XMM-Newton and optical spectra from the Himalayan Chandra Telescope (HCT). Our study confirms that the diffuse structure represents remnant emission from historic AGN activity, likely associated with HCG15-D, some 80-86 Myr ago (based on ageing analysis). We detect significant highly linearly-polarised emission from a diffuse 'ridge'-like structure with a highly ordered magnetic field. Our analysis suggests that this emission is generated by draping of magnetic field lines in the intra-group medium (IGrM), although further exploration with simulations would aid our understanding. We confirm that HCG15-C is a group-member galaxy. Finally, we report the detection of thermal emission associated with a background cluster at redshift z ~ 0.87 projected onto the IGrM of HCG15, which matches the position and redshift of the recent SZ detection of ACT-CL J0207.8+0209.

astro-ph.GA↗

arXiv2024

Bird's-eye View of Molecular Gas across Stephan's Quintet Galaxy Group and Intra-group Medium

We present the large-scale distribution and kinematics of cold molecular gas across the compact galaxy group Stephan's Quintet, based on CO(2-1) observations performed with the Atacama Compact Array (ACA) and CO(1-0) data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We find coherent structures of molecular gas associated with the galaxies and intra-group medium, which follow the distribution of warm H$_{2}$ previously seen with the James Webb Space Telescope (JWST). CO is associated with a ridge of shocked gas that crosses the galaxy group, and with a spiral arm of the intruding galaxy NGC7318b, which interacts with the intra-group medium along the ridge. Although the ridge contains widespread shocks, turbulent gas, and warm H$_{2}$, the CO lines are narrower than elsewhere in Stephan's Quintet (FWHM~25-65 km/s), indicative of settled cold gas. At a distinctly different velocity, CO is found in the active galaxy NGC7319 and Northern star-forming region SQ-A. A bridge of turbulent molecular gas connects NGC7319 with the ridge, covering a gap of ~700 km/s between these structures. The gas excitation ranges from $L'_{\rm CO(2-1)}$/$L'_{\rm CO(1-0)}$ ~ 0.3 in the bridge and SQ-A, to ~0.5 along the ridge, to near unity in the center of NGC7319. We also detect either a molecular outflow or turbulent molecular gas associated with the radio source in NGC7319. These ACA data are part of a program with the Atacama Large Millimeter/submillimeter Array (ALMA) and JWST to study molecular gas physics from the largest to the smallest scales across the intra-group medium of Stephan's Quintet.

astro-ph.GA↗

arXiv2024

A Deep Dive into the NGC 741 Galaxy Group: Insights into a Spectacular Head-Tail Radio Galaxy from VLA, MeerKAT, uGMRT and LOFAR

We present deep, wideband multifrequency radio observations (144 MHz$-$8 GHz) of the remarkable galaxy group NGC 741, which yield crucial insights into the interaction between the infalling head-tail radio galaxy (NGC 742) and the main group. Our new data provide an unprecedentedly detailed view of the NGC 741-742 system, including the shock cone, disrupted jets from NGC 742, the long ($\sim$ 255 kpc) braided southern radio tail, and eastern lobe-like structure, and reveal, for the first time, complex radio filaments throughout the tail and lobe, and a likely vortex ring behind the shock cone. The cone traces the bow shock caused by the supersonic ($\mathcal{M}\sim2$) interaction between the head-tail radio galaxy NGC 742 and the intragroup medium (IGrM) while the ring may have been formed by interaction between the NGC 742 shock and a previously existing lobe associated with NGC 741. This interaction plausibly compressed and re-accelerated the radio plasma. We estimate that shock-heating by NGC 742 has likely injected $\sim$2-5$\times$10$^{57}$ erg of thermal energy into the central 10 kpc cooling region of the IGrM, potentially affecting the cooling and feedback cycle of NGC 741. A comparison with Chandra X-ray images shows that some of the previously detected thermal filaments align with radio edges, suggesting compression of the IGrM as the relativistic plasma of the NGC 742 tail interacts with the surrounding medium. Our results highlight that multi-frequency observations are key to disentangling the complex, intertwined origins of the variety of radio features seen in the galaxy group NGC 741, and the need for simulations to reproduce all the detected features.

astro-ph.GA↗

arXiv2024

Abell 746: A highly disturbed cluster undergoing multiple mergers

We present deep XMM-Newton, Karl Jansky Very Large Array, and upgraded Giant Metrewave Radio Telescope observations of Abell 746, a cluster that hosts a plethora of diffuse emission sources that provide evidence for the acceleration of relativistic particles. Our new XMM-Newton images reveal a complex morphology of the thermal gas with several substructures. We observe an asymmetric temperature distribution across the cluster: the southern regions exhibit higher temperatures, reaching ~9 keV, while the northern regions have lower temperatures (below 4 keV), likely due to a complex merger. We find evidence of four surface brightness edges, of which three are merger-driven shock fronts. Combining our new data with the published LOw-Frequency ARray observations has unveiled the nature of diffuse sources in this system. The bright northwest relic shows thin filaments and high degree of polarization with aligned magnetic field vectors. We detect a density jump, aligned with the fainter relic to the north. To the south, we detect high-temperature regions, consistent with shock-heated regions and density jump coincident with the northern tip of the southern radio structure. Its integrated spectrum shows a high-frequency steepening. Lastly, we find that the cluster hosts large-scale radio halo emission. The comparison of the thermal and nonthermal emission reveals an anticorrelation between the bright radio and X-ray features at the center. Our findings suggest that Abell 746 is a complex system that involves multiple mergers.

astro-ph.CO↗

arXiv2023

Multi-phase gas interactions on subarcsec scales in the shocked IGM of Stephan's Quintet with JWST and ALMA

We combine JWST and HST imaging with ALMA~CO(2-1) spectroscopy to study the highly turbulent multi-phase intergalactic medium (IGM) in Stephan's Quintet on 25-150 pc scales. Previous Spitzer observations revealed luminous H$_2$ line cooling across a 45 kpc-long filament, created by a giant shock-wave, following the collision with an intruder galaxy NGC~7318b. We demonstrate that the MIRI/F1000W/F770W filters are dominated by 0-0~S(3)~H$_2$ and a combination of PAH and 0-0~S(5)~H$_2$ emission. They reveal the dissipation of kinetic energy as massive clouds experience collisions, interactions and likely destruction/re-cycling within different phases of the IGM. In one kpc-scaled structure, warm H$_2$ formed a triangular-shaped head and tail of compressed and stripped gas behind a narrow shell of cold H$_2$. In another region, two cold molecular clumps with very different velocities are connected by an arrow-shaped stream of warm, probably shocked, H$_2$ suggesting a cloud-cloud collision is occurring. In both regions, a high warm-to-cold molecular gas fraction indicates that the cold clouds are being disrupted and converted into warm gas. We also map gas associated with an apparently forming dwarf galaxy. We suggest that the primary mechanism for exciting strong mid-IR H$_2$ lines throughout Stephan's Quintet is through a fog of warm gas created by the shattering of denser cold molecular clouds and mixing/recycling in the post-shocked gas. A full picture of the diverse kinematics and excitation of the warm H$_2$ will require future JWST mid-IR spectroscopy. The current observations reveal the rich variety of ways that different gas phases can interact with one another.

astro-ph.GA↗

arXiv2022

Neutron Tagging following Atmospheric Neutrino Events in a Water Cherenkov Detector

We present the development of neutron-tagging techniques in Super-Kamiokande IV using a neural network analysis. The detection efficiency of neutron capture on hydrogen is estimated to be 26%, with a mis-tag rate of 0.016 per neutrino event. The uncertainty of the tagging efficiency is estimated to be 9.0%. Measurement of the tagging efficiency with data from an Americium-Beryllium calibration agrees with this value within 10%. The tagging procedure was performed on 3,244.4 days of SK-IV atmospheric neutrino data, identifying 18,091 neutrons in 26,473 neutrino events. The fitted neutron capture lifetime was measured as 218 \pm 9 μs.

hep-ex↗

arXiv2022

Spatially-resolved properties of early-type group-dominant galaxies with MUSE: gas content, ionisation mechanisms and metallicity gradients

With the goal of a thorough investigation of the ionised gas and its origin in early-type group-dominant galaxies, we present archival MUSE data for 18 galaxies from the Complete Local-Volume Groups Sample (CLoGS). This data allowed us to study the spatially-resolved warm gas properties, including the morphology of the ionised gas, EW(H$α$) and kinematics as well as the gas-phase metallicity (12 + log(O/H)) of these systems. In order to distinguish between different ionisation mechanisms, we used the emission-line ratios [O III]/H$β$ and [N II]/H$α$ in the BPT diagrams and EW(H$α$). We find that the ionisation sources in our sample have variable impacts at different radii, central regions are more influenced by low-luminosity AGN, while extended regions of LINER-like emission are ionised by other mechanisms with pAGBs photoionisation likely contributing significantly. We classified our sample into three H$α$+[N II] emission morphology types. We calculate the gas-phase metallicity assuming several methods and ionisation sources. In general, 12 + log(O/H) decreases with radius from the centre for all galaxies, independently of nebular morphology type, indicating a metallicity gradient in the abundance profiles. Interestingly, the more extended filamentary structures and all extranuclear star-forming regions present shallow metallicity gradients. Within the uncertainties these extended structures can be considered chemically homogeneous. We suggest that group-dominant galaxies in our sample likely acquired their cold gas in the past as a consequence of one or more mechanisms, e.g. gas-clouds or satellite mergers/accretion and/or cooling flows that contribute to the growth of the ionised gas structures.

astro-ph.GA↗

arXiv2022

Collaborative Experience between Scientific Software Projects using Agile Scrum Development

Developing sustainable software for the scientific community requires expertise in software engineering and domain science. This can be challenging due to the unique needs of scientific software, the insufficient resources for software engineering practices in the scientific community, and the complexity of developing for evolving scientific contexts. While open-source software can partially address these concerns, it can introduce complicating dependencies and delay development. These issues can be reduced if scientists and software developers collaborate. We present a case study wherein scientists from the SuperNova Early Warning System collaborated with software developers from the Scalable Cyberinfrastructure for Multi-Messenger Astrophysics project. The collaboration addressed the difficulties of open-source software development, but presented additional risks to each team. For the scientists, there was a concern of relying on external systems and lacking control in the development process. For the developers, there was a risk in supporting a user-group while maintaining core development. These issues were mitigated by creating a second Agile Scrum framework in parallel with the developers' ongoing Agile Scrum process. This Agile collaboration promoted communication, ensured that the scientists had an active role in development, and allowed the developers to evaluate and implement the scientists' software requirements. The collaboration provided benefits for each group: the scientists actuated their development by using an existing platform, and the developers utilized the scientists' use-case to improve their systems. This case study suggests that scientists and software developers can avoid scientific computing issues by collaborating and that Agile Scrum methods can address emergent concerns.

cs.SE↗