arXiv subjects

Tiziana Venturi

Publications and source records attributed to Tiziana Venturi.

At least 19 recordsLinked to original sources

arXiv2026

Direct imaging of sub-parsec binary SMBHs in the central galaxy of the NGC 5044 group

Binary active galactic nuclei (AGN) consist of two supermassive black holes (SMBHs) hosted in a single galaxy that are simultaneously accreting gas. These systems are key to understanding hierarchical galaxy evolution and represent prime targets for low-frequency gravitational wave (GW) experiments. However, binary AGN remain extremely rare: only a handful are confirmed at separations of a few hundred parsecs, and just one pc-scale binary - in an elliptical galaxy at the center of a galaxy cluster - has been securely and visually identified. Direct imaging of sub-parsec binary AGN, the final stage before the GW regime, has so far been missing. Here we report on Very Long Baseline Array (VLBA) observations of NGC 5044, the central galaxy of the X-ray brightest galaxy group. This galaxy is known to exhibit pc-scale radio jets nearly orthogonal to two older AGN outbursts. The 4.9, 8.4, 15.2, and 23.6 GHz VLBA images reveal two compact, flat-spectrum, and variable radio cores separated by just 0.38 parsec at the heart of the galaxy, forming the tightest directly imaged binary AGN known by an order of magnitude. This discovery suggests that the older outbursts may have been powered by jets from the secondary core, without invoking any reorientation of the primary jet axis. More broadly, comparison with other systems points to massive, cluster-central elliptical galaxies being promising targets to search for binary SMBHs.

astro-ph.GA↗

arXiv2026

A new look at old devils. II: New insights on classical radio galaxies from MeerKAT and uGMRT

This paper presents a detailed morphological and spectral analysis of a sample of ten radio galaxies observed with the MeerKAT in L-band ($856\, \text{-}\,1712\ \mathrm{MHz}$) and the upgraded Giant Metrewave Radio Telescope in Band-4 ($550\,\text{-}\,850\ \mathrm{MHz}$). Our main goals are to revisit the current classification scheme for classical radio galaxies and study the properties of new radio features in jets, lobes and hot spots, which are becoming increasingly numerous due to the sensitivity and imaging capabilities of current radio interferometers, and suggest previous unexplored interaction mechanisms between the radio plasma and the external medium. The sample from the 4C catalogue includes FR I, FR II, wide-angle and narrow-angle tailed sources as well as FR 0 radio galaxies from FR0CAT, with redshifts ranging from $0.04\,\text{-}\,0.20$. The high angular resolution, $\sim4^{\prime\prime}\text{-}10^{\prime\prime}$ total intensity images are presented, revealing complex structures in the jets, lobes and hotspots of these sources. The integrated spectra of the sources, constructed using flux density measurements from our observations and archival data, reveal spectral breaks and slopes indicative of radiative ageing, with ages spanning $\sim40\,\text{-}\,242\ \mathrm{Myr}$. While the sample broadly confirms the classical FR classification as a useful first-order scheme, the substructures within the radio emission of sources highlight the need for models that incorporate environmental complexity and episodic jet activity to fully describe radio-galaxy evolution.

astro-ph.GA↗

arXiv2026

Gamma-ray Bursts in the Radio Sky: the Role of the SKA-VLBI

Radio observations of $γ$-ray bursts (GRBs) employing the very long baseline interferometry (VLBI) technique provide us with fundamental information on the dynamics and the geometry of the GRB blast wave. With its high angular resolution ($\sim$milli-arcsecond), VLBI allows us to measure the apparent superluminal expansion, to characterise the structure of the jet and to constrain the viewing angle and jet opening angle. While this information is crucial to understand these transient events, such studies have been possible only for three GRBs to date, owing to both the poor sensitivity of current radio facilities and the paucity of close and bright GRBs. In this chapter, we estimate the impact that the SKA-Mid will have on these studies, when included in a VLBI network. We performed a series of dedicated simulations of VLBI observations of GRBs, considering five VLBI networks and the SKA-Mid, both in its AA* and AA4 configurations. We show that including the SKA-Mid in a global-VLBI experiment will: (i) allow us to measure the size and the expansion of a GRB up to a redshift $z\simeq 0.25$ (at a confidence level of $3σ$); (ii) constrain the size $\gtrsim$2 times better than the current global-VLBI array; (iii) improve the localisation precision in Declination from 4 to 30 times; (iv) detect the apparent proper motion of GRBs seen slightly off-axis with a confidence level 3 times better than current VLBI networks. Ultimately, the SKA-Mid will open a new window on a portion of the GRB population that has been inaccessible so far.

astro-ph.HE↗

arXiv2026

The SKA View of Cool-core Clusters: Evolution of Radio Mini-halos and AGN Feedback

In about 70 per cent of relaxed, cool-core galaxy clusters, the brightest cluster galaxy (BCG) is radio loud, showing non-thermal radio jets and lobes ejected by the central active galactic nucleus (AGN). In recent years such relativistic plasma has been shown to interact with the surrounding thermal intra-cluster medium (ICM) as revealed by striking images where radio lobe fill the cavities in the X-ray-emitting gas. This "radio-mode feedback" phenomenon is widespread and crucial for understanding the physics of cluster cores and the properties of the central BCG. Mechanically-powerful AGN are expected to drive turbulence in the central ICM which may also contribute to the origin of non-thermal emission on cluster-scales. Diffuse non-thermal emission has been observed in many cool-core clusters in the form of a radio mini-halo surrounding the radio-loud BCG on scales comparable to the cooling radius. Large samples of mini-halos are essential to clarify their origin and their link with the thermal and dynamical properties of clusters, especially in view of future high-resolution X-ray studies with NewAthena X-IFU. All-sky surveys with the SKA-Mid telescope at arcsecond resolution would have the potential to detect up to about 3500 mini-halos at redshift z<1 (compared to the few tens currently known). Deep Tier surveys with the SKA-Mid at sub-arcsecond resolution would further enable a complete census of radio-loud BCGs down to 1.4 GHz powers of 10^23 W/Hz up to z~2. This will provide a comprehensive view of AGN feedback and its role in shaping large scale structures.

astro-ph.CO↗

arXiv2026

The Cosmic Ray Life Cycle in Galaxy Clusters

Within the cosmic web, gravitational energy, linked to the formation and growth of the Universe's largest structures and the activity of active galactic nuclei (AGN), is converted to heat through processes such as turbulence and shock waves. These processes have a fundamental impact on the evolution of galaxy clusters. For example, they lead to the amplification of magnetic fields and the production of cosmic ray (CR) electrons that emit continuum radio waves via synchrotron emission. This produces sources on scales of the entire hosting clusters. These large radio sources in galaxy clusters are often classified based on their morphological appearance as radio halos, cluster radio shocks (radio relics), and other types. To understand the CR acceleration processes in galaxy clusters (and beyond), and to gain a comprehensive view of these sources, including their long-term interactions, SKA telescope should conduct both deep observations of a carefully selected sample of nearby clusters as well as shallower wide-area surveys. Thanks to their capabilities - in particular the sensitivity to polarised and low-frequency emission - SKA-Mid (Bands 1 and 2) and SKA-Low are ideally suited to probing magnetic field structures in galaxy clusters, as well as the large reservoir of low-energy CRs that may be accelerated by yet-unexplored microphysical mechanisms. The high sensitivity to low-frequency emission will also be fundamental to detect the long term actions and interactions of these phenomena over gigayear timescales.

astro-ph.CO↗

arXiv2026

AGN Fueling and Radio Jet Evolution in the Galaxy Group NGC 5044 revealed by VLBA HI Absorption and Proper-Motion Radio Observations

The role of cooling gas in triggering active galactic nucleus (AGN) feedback in the centers of galaxy groups and clusters remains a key open question. NGC 5044, the X-ray brightest galaxy group, hosts the largest known reservoir of molecular gas among cool-core groups and exhibits multiple AGN outbursts, making it an ideal system to study AGN feeding. We present new multi-frequency Very Long Baseline Array (VLBA) observations of NGC 5044 at 1.4 GHz, 4.9 GHz, and 8.4 GHz, combining continuum imaging with HI spectroscopy. At 1.4 GHz, we recovered the previously known symmetric northeast-southwest jets extending for 5.5 pc each, along with evidence for previously undetected, more extended faint emission aligned with the older, kpc-scale outbursts. Comparison of 4.9 GHz and 8.4 GHz data from 2020 and 2024 reveals clear outward proper motion of jet components, yielding an average expansion speed of $(0.10\pm0.02)\,c$ and implying a dynamical age of $\sim$180 yr for the ejection of the parsec-scale jet components. The jet width profile suggests a transition from parabolic to conical collimation at a few $\times 10^{4}$ Schwarzschild radii. We detect a narrow, redshifted HI absorption line at $+264\,\mathrm{km\,s^{-1}}$ against the VLBA core, tracing a compact, cold atomic cloud within $\sim$10-20 pc of the AGN. The close velocity correspondence with previously detected CO and HI absorption features in ALMA and MeerKAT data, respectively, demonstrates that cold atomic and molecular gas coexists in infalling clouds at parsec scales. Overall, these results provide an unprecedented high angular resolution view of AGN cycling, jet growth, and feeding in a galaxy group environment.

astro-ph.GA↗

arXiv2025

A direction-dependent framework for visibility plane mosaicing and primary beam correction

With the increasing sensitivity of modern radio interferometers, it has become important to image objects larger than the field of view while optimising sensitivity and image fidelity. We present a coherent visibility plane direction-dependent imaging, calibration and mosaicing framework. Our simulations and application to real MeerKAT data show that this joint deconvolution and primary beam correction approach, coupled with direction-dependent calibration, allows for deeper mosaics with greater fidelity and increased accuracy of recovered flux densities and spectral indices, especially beyond the half-power beam width. Our best-case mosaic produces precise flux values within a 6% uncertainty and spectral indices within 20\% throughout the imaged area, and is fully complete out to twice the radii and half the flux density than the image plane equivalent. The application to archival wideband MeerKAT 1283 MHz data produces the deepest high-resolution image of the Shapley Supercluster Core, with a sensitivity of 3.6 $μ$Jy/beam within the primary beam at a 7$^{\prime\prime}$ resolution, constituting a $\sim$ 50% increase in dynamic range over the image plane counterpart, and a fluxscale that is consistent within 10% across the entire field of view. The compute time for the direction-dependent visibility plane mosaic was comparable to the sum of the times needed to perform direction-dependent calibration on the individual pointings. Our results suggest that visibility plane mosaicing with its capability for deeper deconvolution could improve the efficiency of deep and wide surveys, particularly for on-the-fly mapping and studies of low surface brightness sources, and could form the basis of future calibration pipelines for SKA-scale instruments.

astro-ph.IM↗

arXiv2025

Multiphase gas offsets in the atmospheres of central galaxies and their consequences for SMBH activation I. The hot and warm ionized gas phases

We investigate the spatial relationships between multi-phase gas components and supermassive black hole (SMBH) activity in a sample of 25 cool core galaxy groups and clusters. Using high angular resolution observations from \textit{Chandra}, VLT/MUSE, and VLBA, we robustly locate the position, respectively, of the X-ray peak of the intracluster medium (ICM), of the H$α$ peak of the warm ionized gas, and of the SMBH radio core on parsec scales. We identify spatial offsets between the X-ray peak of the hot gas and the SMBH in 80% of the systems, with an average displacement of $\langleΔ^{\text{SMBH}}_{\text{X-ray}}\rangle = 4.8$ kpc (dispersion of $3.8$ kpc). In contrast, the peak of warm ionized gas traced by H$α$ exhibits much smaller offsets ($\langleΔ^{\text{SMBH}}_{\text{H}α}\rangle = 0.6$ kpc; dispersion of $1.4$ kpc) and a lower incidence of displacement (15%). Our findings suggest that hot gas sloshing primarily drives the observed spatial offsets, with AGN-driven uplift contributing in some systems.Importantly, systems with H$α$ - SMBH offsets of $\geq$1 kpc uniformly lack detectable radio cores on VLBA scales, with upper limits on the 5~GHz power of $P_{5\,\text{GHz}} \leq 10^{21-22}$ W Hz$^{-1}$, while those without such offsets exhibit radio powerful AGN with pc-scale radio emission up to $P_{5\,\text{GHz}} \sim 10^{24-25}$ W Hz$^{-1}$. This correlation indicates that centrally concentrated warm gas is critical for sustaining radio-loud SMBH activity, possibly supporting scenarios of cold-mode accretion. Overall, our results highlight the importance of high-angular-resolution, multi-wavelength observations for understanding the interplay between multiphase gas cooling and AGN fueling in central galaxies.

astro-ph.GA↗

arXiv2025

The MeerKAT Galaxy Cluster Legacy Survey -- II. Catalogue of the diffuse radio emission in MeerKAT-GCLS clusters

We present a follow-up study focused on cluster-scale diffuse radio emissions in 115 galaxy clusters in the Southern sky, using full-resolution (7.8") and tapered low-resolution (15") images from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). In this MGCLS follow-up paper, we update and quantitatively characterise the presence of diffuse radio emission and provide detailed catalogue information on its radio properties at 1.28 GHz. As the MGCLS sample is heterogeneous and was initially used as a test bed to reveal the scientific potential of MeerKAT, the reported numbers are subject to this special case. More than half ($\sim$54%; 62/115) of the observed MGCLS clusters present diffuse cluster radio emission, with the total number of diffuse radio sources or candidates detected being 103. Including candidates, we find that radio relics are the most frequently detected diffuse sources in MGCLS at 53% (55/103), followed by halos at 32% (33/103) and mini-halos at 10% (11/103), with only 3% (3/103) being Phoenixes. The sizes of the diffuse radio structures and candidates range from 55 kpc to over 2 Mpc, with $P_{1.28GHz}$ radio power ranging from $10^{22}$ W Hz$^{-1}$ to greater than $10^{25}$ W Hz$^{-1}$. In-band radio spectral index estimates reveal revived radio plasma emissions that exhibit steep radio spectral indices down to $α^{1656}_{908} \sim -3.5$. Mini-halos and their respective candidates are detected mainly in low-mass ($M_{500}$ $\leq$ 5$\times10^{14}$ M$_\odot$) and low-power ($P_{1.4GHz}$ $\leq$ $10^{23}$ W Hz$^{-1}$) systems. We suggest the presence of a statistically significant correlation between the 1.4 GHz radio power and the cluster mass for mini-halo (and candidate) systems.

astro-ph.GA↗

arXiv2025

A comparative analysis of GNSS-inferred precipitable water vapour at the potential sites for the Africa Millimetre Telescope

The Event Horizon Telescope (EHT) is a network of antennas across the globe currently used to image super-massive black holes (SMBHs) at a frequency of 230 GHz. Since the release of the image of M87$^\ast$ in 2019 and, subsequently, that of Sgr A$^\ast$ in 2022 by the EHT collaboration, the focus has shifted to dynamically imaging SMBHs. This has led to a search for potential sites to extend and fill in the gaps within the EHT network. The Gamsberg Mountain and the H.E.S.S. site are both located within the Khomas highlands and have been identified as potential sites for the Africa Millimetre Telescope (AMT). Precipitable water vapour (PWV) in the atmosphere is the main source of opacity and noise from atmospheric emissions when observing at millimetre to sub-millimetre wavelengths. This study aims to establish the PWV content and the atmospheric transmission at 86, 230, and 345 GHz at the AMT potential sites using Global Navigation Satellite System (GNSS) derived PWV data. Results show both sites have potential for observations at 86 and 230 GHz, with 345 GHz possible at the Gamsberg Mountain during winter. The overall median PWV of 14.27 mm and 9.25 mm was calculated at the H.E.S.S. site and the Gamsberg Mountain, respectively. The EHT window had PWV medians of 16.62 mm and 11.20 mm at the H.E.S.S. site and Gamsberg Mountain, respectively. Among the two sites, the Gamsberg Mountain had the lowest PWV conditions, therefore making it the most suitable site for the AMT.

astro-ph.IM↗

arXiv2025

Analysis of the accuracy of GNSS inferred precipitable water vapour against that from a 210 GHz WVR at the H.E.S.S. site

The High Energy Stereoscopic System (H.E.S.S.) site and the Gamsberg Mountain have been identified as potential sites for the Africa Millimetre Telescope (AMT). The AMT is poised to observe at millimetre and possibly at submillimetre wavelengths. At these wavelengths, precipitable water vapour (PWV) in the atmosphere is the main source of opacity during observations and therefore needs to be accurately assessed at the potential sites for the AMT. In order to investigate the PWV conditions for the AMT, identical Global Navigation Satellite System (GNSS) stations were installed and used to assess the PWV at the two potential sites. In this study, the accuracy of those PWV measurements by the GNSS stations was assessed by comparing the H.E.S.S. installed GNSS station PWV measurements to that from a 210 GHz Water Vapour Radiometer (WVR) also installed at the H.E.S.S. site. A correlation of 98% and an offset of 0.34 mm was found between the GNSS station and the 210 GHz WVR PWV data when on-site pressure and the Nevada Geodetic Laboratory (NGL) weighted mean temperature ($\mathrm{T_m}$) were used calculate the GNSS station PWV data. In comparison, the offset reduces to 0.15 mm when on-site derived $\mathrm{T_m}$ and pressure were used to calculate the GNSS station PWV. The results show that the GNSS station with on-site meteorological data can be used with high accuracy to reliably determine the PWV conditions at the H.E.S.S. site.

astro-ph.IM↗

arXiv2024

A Repeating Fast Radio Burst Source in a Low-Luminosity Dwarf Galaxy

We present the localization and host galaxy of FRB 20190208A, a repeating source of fast radio bursts (FRBs) discovered using CHIME/FRB. As part of the PRECISE repeater localization program on the EVN, we monitored FRB 20190208A for 65.6 hours at $\sim1.4$ GHz and detected a single burst, which led to its VLBI localization with 260 mas uncertainty (2$σ$). Follow-up optical observations with the MMT Observatory ($i\gtrsim 25.7$ mag (AB)) found no visible host at the FRB position. Subsequent deeper observations with the GTC, however, revealed an extremely faint galaxy ($r=27.32 \pm0.16$ mag), very likely ($99.95 \%$) associated with FRB 20190208A. Given the dispersion measure of the FRB ($\sim580$ pc cm$^{-3}$), even the most conservative redshift estimate ($z_{\mathrm{max}}\sim0.83$) implies that this is the lowest-luminosity FRB host to date ($\lesssim10^8L_{\odot}$), even less luminous than the dwarf host of FRB 20121102A. We investigate how localization precision and the depth of optical imaging affect host association, and discuss the implications of such a low-luminosity dwarf galaxy. Unlike the other repeaters with low-luminosity hosts, FRB 20190208A has a modest Faraday rotation measure of a few tens of rad m$^{-2}$, and EVN plus VLA observations reveal no associated compact persistent radio source. We also monitored FRB 20190208A for 40.4 hours over 2 years as part of the ÉCLAT repeating FRB monitoring campaign on the Nançay Radio Telescope, and detected one burst. Our results demonstrate that, in some cases, the robust association of an FRB with a host galaxy will require both high localization precision, as well as deep optical follow-up.

astro-ph.HE↗

arXiv2024

Probing the high frequency variability of NGC 5044: the key to AGN feedback

The active galactic nucleus (AGN) feeding and feedback process in the centers of galaxy clusters and groups is still not well understood. NGC 5044 is the ideal system in which to study AGN feedback. It hosts the largest known reservoir of cold gas in any cool-core galaxy group, and features several past epochs of AGN feedback imprinted as cavities in the X-ray bright intragroup medium (IGrM), as well as parsec scale jets. We present Submillimeter Array (SMA), Karl G. Jansky Very Large Array (VLA), James Clerk Maxwell Telescope (JCMT), and Atacama Large Millimeter/submillimeter Array (ALMA) high frequency observations of NGC 5044 to assess the time variability of the mmwaveband emission from the accretion disk, and quantify the Spectral Energy Distribution (SED) from the radio to sub-millimeter band. The SED is well described by advection dominated accretion flow (ADAF) model and self-absorbed jet emission from an aging plasma with tau = 1kyr. We find a characteristic variability timescale of 150 days, which constrains the ADAF emission region to about 0.1pc, and the magnetic field to 4.7mG in the jets and and 870G in the accretion disk. A longer monitoring/sampling will allow to understand if the underlying process is truly periodic in nature.

astro-ph.GA↗

arXiv2024

The radio halo in PLCKESZ G171.94 $-$ 40.65: Beacon of merging activity

We present the first multi-frequency analysis of the candidate ultra-steep spectrum radio halo in the galaxy cluster PLCKESZ G171.94$-$40.65, using the upgraded Giant Metrewave Radio telescope (uGMRT; 400 MHz), and Karl G. Jansky Very Large Array (JVLA; 1-2 GHz) observations. Our radio data have been complemented with archival \textit{Chandra} X-ray observations to provide a crucial insight into the complex intracluster medium (ICM) physics, happening at large scales. We detect the radio halo emission to the extent of $\sim$ 1.5 Mpc at 400 MHz, significantly larger than previously reported, along with five tailed galaxies in the central region. We also report the discovery of an unknown diffuse source 'U', at the cluster periphery, with an extent of 300 kpc. Using the available observations, we have found that the radio spectrum of the halo is well-fitted with a single power law, having a spectral index of $-1.36 \pm 0.05$, indicating that it is not an ultra-steep spectrum radio halo. Our low-resolution (25$''$) resolved spectral map shows an overall uniform spectral index, with some patches of fluctuations. The X-ray and radio surface brightness are morphologically co-spatial, with a slight extension along the northwest-southeast direction, seen in both maps. The radio and X-ray surface brightness indicates strong positive correlations, with sub-linear correlation slopes ($\sim$ 0.71). Multiple tailed galaxies and the radio halo indicate a high dynamical activity at the cluster central region.

astro-ph.CO↗

arXiv2024

The Multi-Epoch Jet Outbursts in Abell 496: synchrotron ageing and buoyant X-ray cavities draped by warm gas filaments

The galaxy cluster Abell 496 has been extensively studied in the past for the clear sloshing motion of the hot gas on large scales, but the interplay between the central radio galaxy and the surrounding cluster atmosphere is mostly unexplored. We present a dedicated radio, X-ray, and optical study of Abell 496 aimed at investigating this connection. We use deep radio images obtained with the Giant Metrewave Radio Telescope at 150, 330 and 617 MHz, Very Large Array at 1.4 and 4.8 GHz, and VLA Low Band Ionosphere and Transient Experiment at 340 MHz, with angular resolutions ranging from 0.''5 to 25''. Additionally, we use archival Chandra and Very Large Telescope MUSE observations. The radio images reveal three distinct periods of jet activity: an ongoing episode on sub-kpc scales with an inverted radio spectrum; an older episode that produced lobes on scales $\sim$20 kpc which now have a steep spectral index ($α= 2.0 \pm 0.1$); and an oldest episode that produced lobes on scales of $\sim$50 - 100 kpc with an ultra-steep spectrum ($α= 2.7 \pm 0.2$). Archival Chandra X-ray observations show that the older and oldest episodes have excavated two generations of cavities in the hot gas of the cluster. The outermost X-ray cavity has a clear mushroom-head shape, likely caused by its buoyant rise in the cluster's potential. Cooling of the hot gas is ongoing in the innermost 20 kpc, where H$α$-bright warm filaments are visible in VLT-MUSE data. The H$α$-filaments are stretched towards the mushroom-head cavity, which may have stimulated ICM cooling in its wake. We conclude by commenting on the non-detection of a radio mini-halo in this vigorously sloshing, but low-mass, galaxy cluster.

astro-ph.GA↗

arXiv2024

uGMRT sub-GHz view of the Sausage cluster diffuse radio sources

CIZA J2242.8+5301, or the Sausage cluster, is well studied over a range of frequencies. Since its first discovery, a lot of interesting features and unique characteristics have been uncovered. In this work, we report some more new morphological features using the uGMRT band-3 and band-4 data. In the north relic, we observe variation in spectral index profiles across the relic width from the east to west, which may indicate a decrease in downstream cooling rate in that direction. We re-confirm the presence of an additional ~ 930 kpc relic in the north. We classify the filamentary source in the downstream region to be a narrow angle tail (NAT) radio galaxy. The bright arc in the east relic shows sub-structure in the spectral index profile, which may indicate the presence of finer filaments. We further report the presence of a double-strand structure in the east relic similar to the 'Toothbrush' relic. We categorize the bright 'L' shaped structure in the southern relic to be a NAT radio galaxy, as well as trace the actual ~ 1.1 Mpc relic component. We re-confirm the existence of the faint southern extent, measuring the relic length to be ~ 1.8 Mpc. Furthermore, we suggest the southern relic to be a union of individual component relics rather than a single giant filamentary relic. Lastly, based on the morphological symmetry between northern and southern relics, we suggest a schematic shock structure associated with the merger event in an attempt to explain their formation scenario.

astro-ph.CO↗

arXiv2024

ASKAP reveals the radio tail structure of the Corkscrew Galaxy shaped by its passage through the Abell 3627 cluster

Among the bent tail radio galaxies common in galaxy clusters are some with long, collimated tails (so-called head-tail galaxies) shaped by their interactions with the intracluster medium (ICM). Here we report the discovery of intricate filamentary structure in and beyond the ~28' (570 kpc) long, helical radio tail of the Corkscrew Galaxy (1610-60.5, ESO137-G007), which resides in the X-ray bright cluster Abell 3627 (D = 70 Mpc). Deep radio continuum data were obtained with wide-field Phased Array Feeds on the Australian Square Kilometer Array Pathfinder (ASKAP) at 944 MHz and 1.4 GHz. The Corkscrew Galaxy is located 15' north of the prominent wide-angle tail (WAT) radio galaxy 1610-60.8 (ESO137-G006) near the cluster centre. While the bright (young) part of its radio tail is highly collimated, the faint (old) part shows increasing oscillation amplitudes, break-ups, and filaments. We find a stunning set of arc-shaped radio filaments beyond and mostly orthogonal to the collimated Corkscrew tail end, forming a partial bubble. This may be the first detection of a "proto-lobe" seen in 3D MHD simulations by Nolting et al. (2019), formed by the face-on impact of the Corkscrew Galaxy with a shock front in the cluster outskirts. Interactions of the radio galaxy tail with the ICM are likely responsible for the tail collimation and shear forces within the ICM for its increasingly filamentary structure. We also report the discovery of small (~20-30 kpc) ram-pressure stripped radio tails in four Abell 3627 cluster galaxies.

astro-ph.GA↗

arXiv2023

Milliarcsecond Localisation of the Hyperactive Repeating FRB 20220912A

We present very-long-baseline interferometry (VLBI) observations of the hyperactive repeating FRB 20220912A using the European VLBI Network (EVN) with an EVN-Lite setup. We detected 150 bursts from FRB 20220912A over two observing epochs in October 2022. Combining the data of these bursts allows us to localise FRB 20220912A to a precision of a few milliarcseconds, corresponding to a transverse scale of less than 10 pc at the distance of the source. The precision of this localisation shows that FRB 20220912A lies closer to the centre of its host galaxy than previously found, although still significantly offset from the host galaxy's nucleus. On arcsecond scales, FRB 20220912A is coincident with a persistent continuum radio source known from archival observations, however, we find no compact persistent emission on milliarcsecond scales. The persistent radio emission is thus likely to be from star-formation in the host galaxy. This is in contrast to some other active FRBs, such as FRB 20121102A and FRB 20190520B.

astro-ph.HE↗