A new look at old friends – I. Imaging classical radio galaxies with uGMRT and MeerKAT

We have undertaken a systematic study of FR I and FR II radio galaxies with the upgraded Giant Metrewave Radio Telescope (uGMRT) and MeerKAT. The main goal is to explore whether the unprecedented few μJy sensitivity reached in the range 550–1712 MHz at the resolution of ∼4–7 arcsec reveals new features in the radio emission which might need us to revise our current classification scheme for classical radio galaxies. In this paper, we present the results for the first set of four radio galaxies, i.e. 4C 12.02, 4C 12.03, CGCG 044–046, and CGCG 021–063. The sources have been selected from the 4C sample with well-defined criteria and have been imaged with the uGMRT in the range 550–850 MHz (band 4) and with the MeerKAT in the range 856–1712 MHz (L-band). Full resolution images are presented for all sources in the sample, together with MeerKAT in-band spectral images. Additionally, the uGMRT–MeerKAT spectral image and MeerKAT L-band polarization structure are provided for CGCG 044–046. Our images contain a wealth of morphological details, such as filamentary structure in the emission from the lobes, radio emission beyond the hotspots in three sources, and misalignments. We briefly discuss the overall properties of CGCG 044–046 in the light of the local environment as well, and show possible restarted activity in 4C 12.03 which needs to be confirmed. We conclude that at least for the sources presented here, the classical FR I/FR II morphological classification still holds with the current improved imaging capabilities, but the richness in details also suggests caution in the systematic morphological classification carried out with automatic procedures in surveys with poorer sensitivity and angular resolution.http://mnras.oxfordjournals.orghj2022Physic

Viewing classical radio galaxies with the upgraded GMRT and MeerKAT

We present a progress report of a study of FR I and FR II radio galaxies. Several new morphological features in the radio emission are now revealed using the high (mJy) sensitivity reached in the range 550–1712 MHz, more than a factor of three, at the high ( 400 700) angular resolution with the upgraded Giant Metrewave Radio Telescope (uGMRT) and MeerKAT. Therefore, the aim of this study is to understand if we need to revise our current classification scheme for classical radio galaxies. In order to address our goals, we have carefully constructed a sample of 14 (6 FR I, 6 FR II and 2 FR 0) radio galaxies. The uGMRT and MeerKAT images of our four target sources revealed a wealth of morphological details, e.g., filamentary structure in the emission from the lobes, misalignments, radio emission beyond the hot-spots in three sources, etc.; see Fanaroff et al. (2021). Here, we present preliminary results for two more radio galaxies from our sample using uGMRT, in the light of the local environment. Finally, we are awaiting uGMRT and MeerKAT observations of remaining sample sources. Our results show that for the radio galaxies in this study, the morphological classification scheme for the classical FR I/FR II radio galaxies still holds, even with the improved imaging capabilities of the uGMRT and MeerKAT. Furthermore, we need to be cautious when using automated procedures for classification schemes, e.g., in surveys (with poorer sensitivities and angular resolutions) because of the rich morphological details that are shown in our uGMRT and MeerKAT images.The Department of Atomic Energy, Government of India; the Ministero degli Affari Esteri e della Cooperazione Internazionale, Direzione Generale per la Promozione del Sistema Paese, Progetto di Grande Rilevanza; the South African Research Chairs Initiative of the Department of Science and Technology; the National Research Foundation; the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme; the Italian Minister for Research and Education (MIUR) and the South African Radio Astronomy Observatory.https://www.mdpi.com/journal/galaxiesam2022Physic

MeerKAT-16 HI observation of the dIrr galaxy WLM

We present observations and models of the kinematics and the distribution of the neutral hydrogen (Hi) in the isolated dwarf irregular galaxy, Wolf-Lundmark-Melotte (WLM). We observed WLM with the Green Bank Telescope (GBT) and as part of the MeerKAT Early Science Programme, where 16 dishes were available. The Hi disc of WLM extends out to a major axis diameter of 300 (8.5 kpc), and a minor axis diameter of 200 (5.6 kpc) as measured by the GBT. We use the MeerKAT data to model WLM using the TiRiFiC software suite, allowing us to t di erent tilted-ring models and select the one that best matches the observation. Our nal best- tting model is a at disc with a vertical thickness, a constant inclination and dispersion, and a radially-varying surface brightness with harmonic distortions. To simulate bar- like motions, we include second-order harmonic distortions in velocity in the tangential and the vertical directions. We present a model with only circular motions included and a model with non-circular motions. The latter describes the data better. Overall, the models reproduce the global distribution and the kinematics of the gas, except for some faint emission at the 2 level. We model the mass distribution of WLM with a pseudo-isothermal (ISO) and a Navarro-Frenk-White (NFW) dark matter halo models. The NFW and the ISO models t the derived rotation curves within the formal errors, but with the ISO model giving better reduced chi-square values. The mass distribution in WLM is dominated by dark matter at all radii.The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the Na- tional Research Foundation, an agency of the Department of Science and Innovation. This work is based upon research supported by the South African Research Chairs Initiative of the Department of Sci- ence and Technology and National Research Foundation. The nancial assistance of the South African Radio Astron- omy Observatory (SARAO) towards this research is hereby acknowledged (www.sarao.ac.za). PK is partially supported by the BMBF project 05A17PC2 for D-MeerKAT. AS acknowledges the Russian Science Foundation grant 19-12-00281 and the Program of development of M.V.http://mnras.oxfordjournals.orgam2021Physic

GASP XXVI. HI gas in jellyfish galaxies : the case of JO201 and JO206

Please read abstract in the article.European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme grant agreement no. 679627 and no.833824, project name FORNAX and GASP, respectively. We acknowledge funding from the agreement ASI-INAF n.2017-14-H.0, as well as from the INAF main-stream funding programme. M. R’s research is supported by the SARAO HCD programme via the "New Scientific Frontiers with Precision Radio Interferometry" research group grant. M. R. acknowledges support from the Italian Ministry of Foreign A airs and International Cooperation (MAECI Grant Number ZA18GR02) and the South African Department of Science and Technology’s National Research Foundation (DST-NRF Grant Number 113121) as part of the ISARP RADIOSKY2020 Joint Research Scheme. B. V. and M. G. also acknowledge the Italian PRIN-Miur 2017 (PI A. Cimatti). Y. J. acknowledges financial support from CONICYT PAI (Concurso Nacional de Insercion en la Academia 2017), No. 79170132 and FONDECYT Iniciación 2018 No. 11180558. M. V. acknowledges support by the Netherlands Foundation for Scientific Research (NWO) through VICI grant 016.130.338.http://www.aanda.orgam2020Physic

The extended H i halo of NGC 4945 as seen by MeerKAT

The State Agency for Research of the Spanish Ministry of Science, Innovation and Universities through the ‘Center of Excellence Severo Ochoa’ awarded to the Instituto de Astrofísica de Andalucía; the Economic Transformation, Industry, Knowledge and Universities Council of the Regional Government of Andalusia and the European Regional Development Fund from the European Union; the South African Radio Astronomy Observatory (SARAO); BMBF Verbundforschung; DFG Sonderforschungsbereich and the European Research Council (ERC).http://mnras.oxfordjournals.orghj2022Physic

Anomalous gas in ESO 149-G003 : a MeerKAT-16 view

ESO 149-G003 is a close-by, isolated dwarf irregular galaxy. Previous observations with the ATCA indicated the presence of anomalous neutral hydrogen (⁠HI⁠) deviating from the kinematics of a regularly rotating disc. We conducted follow-up observations with the MeerKAT radio telescope during the 16-dish Early Science programme as well as with the MeerLICHT optical telescope. Our more sensitive radio observations confirm the presence of anomalous gas in ESO 149-G003, and further confirm the formerly tentative detection of an extraplanar HI component in the galaxy. Employing a simple tilted-ring model, in which the kinematics is determined with only four parameters but including morphological asymmetries, we reproduce the galaxy’s morphology, which shows a high degree of asymmetry. By comparing our model with the observed HI⁠, we find that in our model, we cannot account for a significant (but not dominant) fraction of the gas. From the differences between our model and the observed data cube, we estimate that at least 7–8 per cent of the HI in the galaxy exhibits anomalous kinematics, while we estimate a minimum mass fraction of less than 1 per cent for the morphologically confirmed extraplanar component. We investigate a number of global scaling relations and find that, besides being gas-dominated with a neutral gas-to-stellar mass ratio of 1.7, the galaxy does not show any obvious global peculiarities. Given its isolation, as confirmed by optical observations, we conclude that the galaxy is likely currently acquiring neutral gas. It is either re-accreting gas expelled from the galaxy or accreting pristine intergalactic material.http://mnras.oxfordjournals.orghj2022Physic

The MeerKAT Galaxy Cluster Legacy Survey: I. Survey overview and highlights

Please abstract in the article.The South African Radio Astronomy Observatory (SARAO), the National Research Foundation (NRF), the National Radio Astronomy Observatory, US National Science Foundation, the South African Research Chairs Initiative of the DSI/NRF, the SARAO HCD programme, the South African Research Chairs Initiative of the Department of Science and Innovation.http://www.aanda.orghj2022Physic

HI disks in nearby galaxies from the HALOGAS survey

The HALOGAS (Hydrogen Accretion in LOcal GAlaxieS) survey with the Westerbork Synthesis Radio Telescope is the most sensitive systematic survey of the diffuse neutral hydrogen component in nearby spiral galaxies so far. The 5-sigma column density sensitivity reached for the sample of 22 galaxies is ~10^19 atoms cm^-2 over the typical line width of the neutral gas in our target galaxies. The 3D observations are sensitive enough to perform detailed kinematical and dynamical analyses of the extended (vertical) disk structure of our targets. Additionally, we are able to provide a census of the complete cold neutral cloud population above the mass detection limit for individual objects of 10^5 solar masses on average. Our results are relevant in the context of theories describing star formation feedback on the gaseous interface of the galaxy disks with their surroundings, as well as gas accretion from the intergalactic medium. Most notably, we find that the presence of anomalous, slowly rotating extraplanar gas is related to the star formation surface density. I will present the consequences of our observations for the current accretion in local galaxies, and discuss the implied constraints on the accretion process more generally

MeerKAT's discovery of a radio relic in the bimodal merging cluster A2384

We present the discovery of a single radio relic located at the edge of the galaxy cluster A2384, using the MeerKAT radio telescope. A2384 is a nearby (z = 0.092), low mass, complex bimodal, merging galaxy cluster that displays a dense X-ray lament ( 700 kpc in length) between A2384(N) (Northern cluster) and A2384(S) (Southern cluster). The origin of the radio relic is puzzling. By using the MeerKAT observation of A2384, we estimate that the physical size of the radio relic is 824 264 kpc2 and that it is a steep spectrum source. The radio power of the relic is P1:4GHz (3.87 0.40) 1023 W Hz1. This radio relic could be the result of shock wave propagation during the passage of the low-mass A2384(S) cluster through the massive A2384(N) cluster, creating a trail appearing as a hot X-ray lament. In the previous GMRT 325 MHz observation we detected a peculiar FR I radio galaxy interacting with the hot X-ray lament of A2384, but the extended radio relic was not detected; it was confused with the southern lobe of the FR I galaxy. This newly detected radio relic is elongated and perpendicular to the merger axis, as seen in other relic clusters. In addition to the relic, we notice a candidate radio ridge in the hot X-ray lament. The physical size of the radio ridge source is 182 129 kpc2. Detection of the di use radio sources in the X-ray lament is a rare phenomenon, and could be a new class of radio source found between the two merging clusters of A2384(N) and A2384(S).The South African Radio Astronomy Observatory (SARAO)http://mnras.oxfordjournals.orgam2021Physic

MeerKAT-64 discovers wide-spread tidal debris in the nearby NGC 7232 galaxy group

Please read abstract in the article.http://mnras.oxfordjournals.orghj2022Physic