Journal articles: 'Fanaroff-Riley class I'

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V Bicknell, Geoffrey. "Extragalactic Radio Sources and the Role of Relativistic Jets." Australian Journal of Physics 47, no. 5 (1994): 669. http://dx.doi.org/10.1071/ph940669.

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This paper summarises some of the ideas surrounding the role of relativistic jets in radio galaxies and quasars and describes work presented in two recent papers (Bicknell 1994a,b) relating relativistic jets to the Fanaroff~Riley classification of radio galaxies. I conclude with some speculation on the evolutionary connection between Fanaroff~Riley Class I and Class II radio galaxies and the relationship between mergers and radio galaxies, an idea which was discussed at the time of the discovery of Cygnus A and Ccntaurus A.

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Meier, D. L., P. Godon, S. Edgington, D. G. Payne, and K. R. Lind. "11.18. The magnetic switch and the FR I/FR II break." Symposium - International Astronomical Union 184 (1998): 491–92. http://dx.doi.org/10.1017/s0074180900085727.

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Maslej-Krešňáková, Viera, Khadija El Bouchefry, and Peter Butka. "Morphological classification of compact and extended radio galaxies using convolutional neural networks and data augmentation techniques." Monthly Notices of the Royal Astronomical Society 505, no. 1 (May 17, 2021): 1464–75. http://dx.doi.org/10.1093/mnras/stab1400.

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ABSTRACT Machine-learning techniques have been increasingly used in astronomical applications and have proven to successfully classify objects in image data with high accuracy. The current work uses archival data from the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) to classify radio galaxies into four classes: Fanaroff–Riley Class I (FRI), Fanaroff–Riley Class II (FRII), Bent-Tailed (BENT), and Compact (COMPT). The model presented in this work is based on Convolutional Neural Networks (CNNs). The proposed architecture comprises three parallel blocks of convolutional layers combined and processed for final classification by two feed-forward layers. Our model classified selected classes of radio galaxy sources on an independent testing subset with an average of 96 per cent for precision, recall, and F1 score. The best selected augmentation techniques were rotations, horizontal or vertical flips, and increase of brightness. Shifts, zoom, and decrease of brightness worsened the performance of the model. The current results show that model developed in this work is able to identify different morphological classes of radio galaxies with a high efficiency and performance.

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Laing, R. A., D. Guidetti, A. H. Bridle, P. Parma, and M. Bondi. "Deep imaging of Fanaroff-Riley Class I radio galaxies with lobes." Monthly Notices of the Royal Astronomical Society 417, no. 4 (August 31, 2011): 2789–808. http://dx.doi.org/10.1111/j.1365-2966.2011.19436.x.

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Meier, D. L., P. Godon, S. Edgington, D. G. Payne, and K. R. Lind. "The Magnetic Switch as the Origin of the FR I/FR II Break." International Astronomical Union Colloquium 164 (1998): 51–52. http://dx.doi.org/10.1017/s0252921100044481.

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AbstractWe propose that the Fanaroff & Riley division between class I and class II radio sources has its origins in the coronae of magnetized accretion disks around black holes. The “magnetic switch”, an effect that critically controls the speed of jets produced by such disks, can explain both qualitative and quantitative differences in the properties of the two classes. These include why morphology and jet speed are functions of radio power and why the division between the two classes is a strong function of galaxy optical luminosity.

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Parma, P., H. R. DE RUITER, and R. Fanti. "Low Luminosity Radio Galaxies." Symposium - International Astronomical Union 175 (1996): 137–42. http://dx.doi.org/10.1017/s0074180900080335.

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This review talk will deal almost exclusively with the radio aspects of low luminosity radio galaxies, as the other wavelength bands (optical, X, IR) are covered by others during this conference. By low radio luminosity we mean a radio power at 20 cm in the range 1019 to 1024,5 W Hz–1 (Hubble constant of 100, as throughout this talk). At the upper limit occurs the “break” in the radio luminosity (RLF) (Auriemma et al 1977) as well as the transition from Fanaroff -Riley type I to type II (Fanaroff & Riley, 1974). This limitation to weak radio powers does not necessarily imply that such radio sources constitute a homogeneous class of objects; it has been shown by Wrobel & Heeschen (1991) that a number of radio galaxies of very low luminosity have a ratio between far-infrared and radio emission similar to spiral galaxies and this might suggest that these objects are powered by star formation phenomena. Long baseline interferometry is able to pinpoint compact radio nuclei and therefore can distinguish starburst related radio sources from those powered by nuclear activity (see Slee et al 1994).

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Bicknell, G. V. "The Relationship of the Fanaroff-Riley Classification of Extragalactic Radio Sources to Jet Physics." Publications of the Astronomical Society of Australia 6, no. 2 (1985): 130–37. http://dx.doi.org/10.1017/s1323358000017926.

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AbstractThe Class I/Class II division of extragalactic radio sources by Fanaroff-Riley is a manifestation of important physical differences existing in radio sources.It is proposed that the division essentially arises from the differing Mach numbers in Class I and Class II jets. The low Mach number, Class I jets are susceptible to turbulence, are decelerated by entrainment of the surrounding medium and maintain an anomalously high surface brightness as a result. The high Mach number, Class II jets are less turbulent and remain supersonic, produce high pressure shocks along their lengths and terminate via a strong shock against the IGM.An analysis of the energy balance in both types of source reveals jet velocities of the order of 5-10,000 km s-1 for Class I jets and mildly relativistic velocities for Class II jets.The important rôle of optical and X-ray observations in determining the gravitational field of pressure distribution in radio galaxies will be discussed with examples given of NGC1399 and IC4296.

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Bicknell, G. V. "Turbulent jets and the energy budget in Fanaroff–Riley class-I radio sources." Canadian Journal of Physics 64, no. 4 (April 1, 1986): 495–500. http://dx.doi.org/10.1139/p86-093.

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There are good reasons, based upon laboratory data and jet morphology, for believing that the jets in Fanaroff–Riley class-I radio sources are turbulently expanding and decelerating owing to the related entrainment. This provides a simple explanation for the usual slow decline of jet-surface brightness in class-I radio sources. A turbulent jet model in which the velocity variation is inferred from the spreading rate is presented and applied to the main jet in NGC 315. Besides providing a reasonable fit to the surface-brightness variation, the model provides the following simple explanation for the collimation behaviour of this jet. Initially, the jet is turbulent but becomes nonturbulent owing to the effect of an increasing Mach number and a favourable pressure gradient causing the jet to collimate. As the pressure flattens out to the background pressure, the jet becomes turbulent again and starts to re-expand. Various implications of the energy budget for the estimation of jet velocity and density are examined, and further implications of the model are discussed.

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Carvalho, Joel C. "On the Age of GPS Radio Sources." Symposium - International Astronomical Union 159 (1994): 424. http://dx.doi.org/10.1017/s0074180900176090.

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The GHz-Peaked-Spectrum (GPS) radio sources are galaxies and quasars with compact structures on scales of tens to hundreds of parsecs and spectrum peaking around 1 GHz. Phillips and Mutel (1982) suggested that the double GPS sources (also called compact doubles, CD) are an early stage of the evolution of the classical double sources of Fanaroff-Riley class II type. We have presented a model (Carvalho, 1985) in which we show that the properties of the CD sources are consistent with such a scenario. Their ages would be of the order of 104 yr.

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Jones, Paul A., and Ben D. Lloyd. "FR I Jets in Southern Radio Galaxies." Symposium - International Astronomical Union 175 (1996): 143–44. http://dx.doi.org/10.1017/s0074180900080347.

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Sources flagged as extended or multiple in the Molonglo Reference Catalogue (MRC, Large et al. 1981, 1991), south of δ = −30°, were observed with the Molonglo Observatory Synthesis Telescope (MOST) with a resolution of 44 arcsec at 843 MHz (Jones and McAdam 1992) to give a sample of 193 southern extended sources. Optical identifications were made using the UKST bJ sky survey. We are now using the Australia Telescope Compact Array (ATCA) near Narrabri in Australia to study a subsample of Fanaroff-Riley class I radio galaxies and fit models to the jets.

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Huarte-Espinosa, M., M. Krause, and P. Alexander. "Interaction of Fanaroff-Riley class II radio jets with a randomly magnetized intracluster medium." Monthly Notices of the Royal Astronomical Society 418, no. 3 (November 14, 2011): 1621–39. http://dx.doi.org/10.1111/j.1365-2966.2011.19545.x.

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Perucho, M., J. M. Martí, R. A. Laing, and P. E. Hardee. "On the deceleration of Fanaroff–Riley Class I jets: mass loading by stellar winds." Monthly Notices of the Royal Astronomical Society 441, no. 2 (May 8, 2014): 1488–503. http://dx.doi.org/10.1093/mnras/stu676.

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Jones, Paul A. "The Jets in Radio Galaxy B1308–441." Publications of the Astronomical Society of Australia 13, no. 3 (June 1996): 218–26. http://dx.doi.org/10.1017/s1323358000020889.

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AbstractThe giant radio galaxy B1308–441 has prominent two-sided jets, typical of Fanaroff–Riley class I radio galaxies, but there is an unusual bright spot in the SE jet 2 arcmin from the core that gives a marked asymmetry to the source. Observations at 1·37 and 2·37 GHz with the Australia Telescope Compact Array show that the bright spot has a flattened spectrum and high polarisation, and changes the direction of the SE jet. There is a diffuse optical object close to the bright spot which may be related to a shock in the jet.

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Scaife, Anna M. M., and Fiona Porter. "Fanaroff–Riley classification of radio galaxies using group-equivariant convolutional neural networks." Monthly Notices of the Royal Astronomical Society 503, no. 2 (February 26, 2021): 2369–79. http://dx.doi.org/10.1093/mnras/stab530.

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ABSTRACT Weight sharing in convolutional neural networks (CNNs) ensures that their feature maps will be translation-equivariant. However, although conventional convolutions are equivariant to translation, they are not equivariant to other isometries of the input image data, such as rotation and reflection. For the classification of astronomical objects such as radio galaxies, which are expected statistically to be globally orientation invariant, this lack of dihedral equivariance means that a conventional CNN must learn explicitly to classify all rotated versions of a particular type of object individually. In this work we present the first application of group-equivariant convolutional neural networks to radio galaxy classification and explore their potential for reducing intra-class variability by preserving equivariance for the Euclidean group E(2), containing translations, rotations, and reflections. For the radio galaxy classification problem considered here, we find that classification performance is modestly improved by the use of both cyclic and dihedral models without additional hyper-parameter tuning, and that a D16 equivariant model provides the best test performance. We use the Monte Carlo Dropout method as a Bayesian approximation to recover epistemic uncertainty as a function of image orientation and show that E(2)-equivariant models are able to reduce variations in model confidence as a function of rotation.

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Guidetti, D., R. A. Laing, M. Murgia, F. Govoni, L. Gregorini, and P. Parma. "Structure of the magnetoionic medium around the Fanaroff-Riley Class I radio galaxy 3C 449." Astronomy and Astrophysics 514 (May 2010): A50. http://dx.doi.org/10.1051/0004-6361/200913872.

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Huarte-Espinosa, M., M. Krause, and P. Alexander. "3D magnetohydrodynamic simulations of the evolution of magnetic fields in Fanaroff-Riley class II radio sources." Monthly Notices of the Royal Astronomical Society 417, no. 1 (August 1, 2011): 382–99. http://dx.doi.org/10.1111/j.1365-2966.2011.19271.x.

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Bastien, David J., Anna M. M. Scaife, Hongming Tang, Micah Bowles, and Fiona Porter. "Structured variational inference for simulating populations of radio galaxies." Monthly Notices of the Royal Astronomical Society 503, no. 3 (March 15, 2021): 3351–70. http://dx.doi.org/10.1093/mnras/stab588.

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ABSTRACT We present a model for generating postage stamp images of synthetic Fanaroff–Riley Class I and Class II radio galaxies suitable for use in simulations of future radio surveys such as those being developed for the Square Kilometre Array. This model uses a fully connected neural network to implement structured variational inference through a variational autoencoder and decoder architecture. In order to optimize the dimensionality of the latent space for the autoencoder, we introduce the radio morphology inception score (RAMIS), a quantitative method for assessing the quality of generated images, and discuss in detail how data pre-processing choices can affect the value of this measure. We examine the 2D latent space of the VAEs and discuss how this can be used to control the generation of synthetic populations, whilst also cautioning how it may lead to biases when used for data augmentation.

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Saikia, D. J., W. Junor, T. J. Cornwell, T. W. B. Muxlow, and P. Shastri. "A VLA and MERLIN study of extragalactic radio sources with one-sided structure." Monthly Notices of the Royal Astronomical Society 245, no. 3 (August 1, 1990): 408. http://dx.doi.org/10.1093/mnras/245.3.408.

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Summary To investigate the nature of extragalactic radio sources with extended emission on only one side of the active nucleus, we have observed a sample of suspected candidates with both the VLA and MERLIN. In this paper, we present observations of 13 sources which were either suspected of being ‘one-sided’ or were known to have lobes of very different surface brightnesses. Many of the candidates were found to have emission on both sides of the nucleus. Using our observations as well as those available in the literature, we have compiled a sample of 4C quasars having one-sided radio structure. We have then compared some of their properties with a sample of 4C quasars which are two-sided, in order to determine whether their apparently onesided structure is due to relativistic beaming in sources inclined at small angles to the line-of-sight. We find that the median values of fc, the fraction of emission from the core used as a statistical measure of source orientation, and l, their projected linear sizes are consistent with the hypothesis that the one-sided quasars are seen at smaller angles to the line-of-sight than the two-sided ones. We also suggest that the ϕ-fc relation for quasars, where ϕ is the angle between the core polarization vector and the overall radio axis, is consistent with this model, and discuss how the lobe depolarization properties may be useful for further investigations of this interpretation. The velocities required to explain the apparently one-sided quasars in the relativistic beaming framework are in the range of ˜ 0.2-0.8 c. The scarcity of highluminosity, Fanaroff-Riley class II radio galaxies with one-sided structure is consistent with the suggestion that they are at larger angles to the line-of-sight than quasars. In this case, the core-dominated radio galaxies are possibly the lowluminosity, Fanaroff-Riley class I radio galaxies seen at small angles to the line-ofsight, manifesting themselves as BL Lac objects in the more extreme cases.

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Macconi, D., E. Torresi, P. Grandi, B. Boccardi, and C. Vignali. "Radio morphology–accretion mode link in Fanaroff–Riley type II low-excitation radio galaxies." Monthly Notices of the Royal Astronomical Society 493, no. 3 (February 27, 2020): 4355–66. http://dx.doi.org/10.1093/mnras/staa560.

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ABSTRACT Fanaroff–Riley type II (FR II) low-excitation radio galaxies (LERGs) are characterized by weak nuclear excitation on parsec-scales and properties typical of powerful FR IIs (defined as high-excitation radio galaxies, hereafter HERGs/BLRGs) on kiloparsec-scales. Since a link between the accretion properties and the power of the produced jets is expected both from theory and observations, their nature is still debated. In this work, we investigate the X-ray properties of a complete sample of 19 FR II-LERGs belonging to the 3CR catalogue, exploiting Chandra and XMM–Newton archival data. We also analyse 32 FR II-HERGs/BLRGs with Chandra data as a control sample. We compared FR II-LERG and FR II-HERG/BLRG X-ray properties and optical data available in literature to obtain a wide outlook of their behaviour. The low accretion rate estimates for FR II-LERGs, from both X-ray and optical bands, allow us to firmly reject the hypothesis as they are the highly obscured counterpart of powerful FR II-HERGs/BLRGs. Therefore, at least two hypothesis can be invoked to explain the FR II-LERG nature: (i) they are evolving from classical FR IIs because of the depletion of accreting cold gas in the nuclear region, while the extended radio emission is the heritage of a past efficiently accreting activity; and (ii) they are an intrinsically distinct class of objects with respect to classical FR Is/FR IIs. Surprisingly, in this direction, a correlation between accretion rates and environmental richness is found in our sample. The richer the environment is, the more inefficient is the accretion. In this framework, the FR II-LERGs are intermediate between FR Is and FR II-HERGs/BLRGs both in terms of accretion rate and environment.

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Laing, R. A., A. H. Bridle, P. Parma, and M. Murgia. "Structures of the magnetoionic media around the Fanaroff-Riley Class I radio galaxies 3C 31 and Hydra A." Monthly Notices of the Royal Astronomical Society 391, no. 2 (December 1, 2008): 521–49. http://dx.doi.org/10.1111/j.1365-2966.2008.13895.x.

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Lloyd, Ben D., and Paul A. Jones. "Jets in the Fanaroff-Riley class I radio galaxies PKS B1234−723, MRC 1452−517 and PKS B2148−555." Monthly Notices of the Royal Astronomical Society 331, no. 3 (April 2002): 717–30. http://dx.doi.org/10.1046/j.1365-8711.2002.05239.x.

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Yates-Jones, Patrick M., Stanislav S. Shabala, and Martin G. H. Krause. "Dynamics of relativistic radio jets in asymmetric environments." Monthly Notices of the Royal Astronomical Society 508, no. 4 (October 13, 2021): 5239–50. http://dx.doi.org/10.1093/mnras/stab2917.

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ABSTRACT We have carried out relativistic three-dimensional simulations of high-power radio sources propagating i,nto asymmetric cluster environments. We offset the environment by 0 or 1 core radii (equal to 144 kpc), and incline the jets by 0, 15, or 45° away from the environment centre. The different environment encountered by each radio lobe provides a unique opportunity to study the effect of environment on otherwise identical jets. We find that the jets become unstable towards the end of the simulations, even with a Lorentz factor of 5; they nevertheless develop typical Fanaroff–Riley class II radio morphology. The jets propagating into denser environments have consistently shorter lobe lengths and brighter hotspots, while the axial ratio of the two lobes is similar. We reproduce the recently reported observational anticorrelation between lobe length asymmetry and environment asymmetry, corroborating the notion that observed large-scale radio lobe asymmetry can be driven by differences in the underlying environment.

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Meier, D. L. "A Magnetically Switched, Rotating Black Hole Model for the Production of Extragalactic Radio Jets and the Fanaroff and Riley Class Division." Astrophysical Journal 522, no. 2 (September 10, 1999): 753–66. http://dx.doi.org/10.1086/307671.

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Andreasyan, Ruben, M. Hovhannisyan, G. Paronyan, and H. Abrahamyan. "Study of some morphological features of extragalactic radio sources of FRI and FRII types." Proceedings of the International Astronomical Union 9, S304 (October 2013): 104–5. http://dx.doi.org/10.1017/s1743921314003470.

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AbstractIt was used the date of more than 650 extragalactic radio sources for the study of distribution of spectral indexes and elongation for the radio sources of different Fanaroff Riley (FR) classes. It was shown, that no large differences are observed in the distribution of spectral indexes in radio sources FRI and FRII classes. From the study of distribution of the elongation of extragalactic radio sources it was found the following basic morphological differences for the objects of different FR classes: a) the radio images of extragalactic radio sources FRII type in the average are more elongated than the radio images of extragalactic radio sources FRI type: b) the extragalactic radio sources FRI type can be divided on two subtypes with two function of distribution of the elongation parameter K having different maximums. These two subtypes of radio sources of FRI class, in besides of different average elongation of radio images, probably must have also differences in the orientations of these elongation directions relative to the direction of rotation axes of parent optical galaxies that in most cases are coincide with the minor optical axes of galaxies.

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Mingo, B., J. H. Croston, P. N. Best, K. J. Duncan, M. J. Hardcastle, R. Kondapally, I. Prandoni, et al. "Accretion mode versus radio morphology in the LOFAR Deep Fields." Monthly Notices of the Royal Astronomical Society 511, no. 3 (February 16, 2022): 3250–71. http://dx.doi.org/10.1093/mnras/stac140.

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ABSTRACT Radio-loud active galaxies have two accretion modes [radiatively inefficient (RI) and radiatively efficient (RE)], with distinct optical and infrared signatures, and two jet dynamical behaviours, which in arcsec- to arcmin-resolution radio surveys manifest primarily as centre- or edge-brightened structures [Fanaroff–Riley (FR) class I and II]. The nature of the relationship between accretion mode and radio morphology (FR class) has been the subject of long debate. We present a comprehensive investigation of this relationship for a sample of 286 well-resolved radio galaxies in the LOFAR Two-metre Sky Survey Deep Fields (LoTSS-Deep) first data release, for which robust morphological and accretion mode classifications have been made. We find that two-thirds of luminous FRII radio galaxies are RI, and identify no significant differences in the visual appearance or source dynamic range (peak/mean surface brightness) of the RI and RE FRIIs, demonstrating that both RI and RE systems can produce FRII structures. We also find a significant population of low-luminosity FRIIs (predominantly RI), supporting our earlier conclusion that FRII radio structures can be produced at all radio luminosities. We demonstrate that in the luminosity range where both morphologies are present, the probability of producing FRI or FRII radio morphology is directly linked to stellar mass, while across all morphologies and luminosities, RE accretion occurs in systems with high specific star formation rate, presumably because this traces fuel availability. In summary, the relationship between accretion mode and radio morphology is very indirect, with host-galaxy environment controlling these two key parameters in different ways.

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Balmaverde, B., A. Capetti, A. Marconi, G. Venturi, M. Chiaberge, R. D. Baldi, S. Baum, et al. "The MURALES survey." Astronomy & Astrophysics 632 (December 2019): A124. http://dx.doi.org/10.1051/0004-6361/201935544.

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We present observations of a complete sub-sample of 20 radio galaxies from the Third Cambridge Catalog (3C) with redshift < 0.3 obtained from VLT/MUSE optical integral field spectrograph. These data have been obtained as part of the survey MURALES (a MUse RAdio Loud Emission line Snapshot survey) with the main goal of exploring the active galactic nuclei (AGN) feedback process in a sizeable sample of the most powerful radio sources at low redshift. We present the data analysis and, for each source, the resulting emission line images and the 2D gas velocity field. Thanks to their unprecedented depth (the median 3σ surface brightness limit in the emission line maps is 6 × 10−18 erg s−1 cm−2 arcsec−2), these observations reveal emission line structures extending to several tens of kiloparsec in most objects. In nine sources the gas velocity shows ordered rotation, but in the other cases it is highly complex. 3C sources show a connection between radio morphology and emission line properties. Whereas, in three of the four Fanaroff and Riley Class I radio galaxies (FR Is), the line emission regions are compact, ∼1 kpc in size; in all but one of the Class II radiogalaxies FR IIs, we detected large scale structures of ionized gas with a median extent of 17 kpc. Among the FR IIs, those of high and low excitation show extended gas structures with similar morphological properties, suggesting that they both inhabit regions characterized by a rich gaseous environment on kpc scale.

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Wang, Xingzhu, Jiyu Wei, Yang Liu, Jinhao Li, Zhen Zhang, Jianyu Chen, and Bin Jiang. "Research on Morphological Detection of FR I and FR II Radio Galaxies Based on Improved YOLOv5." Universe 7, no. 7 (June 25, 2021): 211. http://dx.doi.org/10.3390/universe7070211.

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Recently, astronomy has witnessed great advancements in detectors and telescopes. Imaging data collected by these instruments are organized into very large datasets that form data-oriented astronomy. The imaging data contain many radio galaxies (RGs) that are interesting to astronomers. However, considering that the scale of astronomical databases in the information age is extremely large, a manual search of these galaxies is impractical given the need for manual labor. Therefore, the ability to detect specific types of galaxies largely depends on computer algorithms. Applying machine learning algorithms on large astronomical data sets can more effectively detect galaxies using photometric images. Astronomers are motivated to develop tools that can automatically analyze massive imaging data, including developing an automatic morphological detection of specified radio sources. Galaxy Zoo projects have generated great interest in visually classifying galaxy samples using CNNs. Banfield studied radio morphologies and host galaxies derived from visual inspection in the Radio Galaxy Zoo project. However, there are relatively more studies on galaxy classification, while there are fewer studies on galaxy detection. We develop a galaxy detection model, which realizes the location and classification of Fanaroff–Riley class I (FR I) and Fanaroff–Riley class II (FR II) galaxies. The field of target detection has also developed rapidly since the convolutional neural network was proposed. You Only Look Once: Unified, Real-Time Object Detection (YOLO) is a neural-network-based target detection model proposed by Redmon et al. We made several improvements to the detection effect of dense galaxies based on the original YOLOv5, mainly including the following. (1) We use Varifocal loss, whose function is to weigh positive and negative samples asymmetrically and highlight the main sample of positive samples in the training phase. (2) Our neural network model adds an attention mechanism for the convolution kernel so that the feature extraction network can adjust the size of the receptive field dynamically in deep convolutional neural networks. In this way, our model has good adaptability and effect for identifying galaxies of different sizes on the picture. (3) We use empirical practices suitable for small target detection, such as image segmentation and reducing the stride of the convolutional layers. Apart from the three major contributions and novel points of the model, the thesis also included different data sources, i.e., radio images and optical images, aiming at better classification performance and more accurate positioning. We used optical image data from SDSS, radio image data from FIRST, and label data from FR Is and FR IIs catalogs to create a data set of FR Is and FR IIs. Subsequently, we used the data set to train our improved YOLOv5 model and finally realize the automatic classification and detection of FR Is and FR IIs. Experimental results prove that our improved method achieves better performance. mAP@0.5 of our model reaches 82.3%, and the location (Ra and Dec) of the galaxies can be identified more accurately. Our model has great astronomical significance. For example, it can help astronomers find FR I and FR II galaxies to build a larger-scale galaxy catalog. Our detection method can also be extended to other types of RGs. Thus, astronomers can locate the specific type of galaxies in a considerably shorter time and with minimum human intervention, or it can be combined with other observation data (spectrum and redshift) to explore other properties of the galaxies.

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Bernhard, E., C. N. Tadhunter, J. C. S. Pierce, D. Dicken, J. R. Mullaney, R. Morganti, C. Ramos Almeida, and E. Daddi. "Quantifying the cool ISM in radio AGNs: evidence for late-time retriggering by galaxy mergers and interactions." Monthly Notices of the Royal Astronomical Society 512, no. 1 (February 23, 2022): 86–103. http://dx.doi.org/10.1093/mnras/stac474.

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ABSTRACT We use deep Herschel observations of the complete 2Jy sample of powerful radio active galactic nuclei (AGNs) in the local Universe (0.05 < z < 0.7) to probe their cool interstellar medium (ISM) contents and star-forming properties, comparing them against other samples of nearby luminous AGNs and quiescent galaxies. This allows us to investigate triggering and feedback mechanisms. We find that the dust masses of the strong-line radio galaxies (SLRGs) in our sample are similar to those of radio-quiet quasars, and that their median dust mass (Mdust = 2 × 107 M⊙) is enhanced by a factor of ∼200 compared to that of non-AGN ellipticals, but lower by a factor of ∼16 relative to that of local ultraluminous infrared galaxies (ULIRGs). Along with compelling evidence for merger signatures in optical images, the SLRGs in our sample also show relatively high star formation efficiencies, despite the fact that many of them fall below the main sequence for star-forming galaxies. Together, these results suggest that most of our SLRGs have been retriggered by late-time mergers that are relatively minor in terms of their gas contents. In comparison with the SLRGs, the radio AGNs with weak optical emission lines (weak-line radio galaxies – WLRGs) and edge-darkened radio jets (Fanaroff–Riley Class I radio sources – FRIs) have both lower cool ISM masses and star formation rates (by a factor of >30), consistent with being fuelled by a different mechanism (e.g. the direct accretion of hot gas).

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Gupta, N., R. Srianand, E. Momjian, G. Shukla, F. Combes, J. K. Krogager, P. Noterdaeme, and P. Petitjean. "H i Gas Playing Hide-and-seek around a Powerful FRI-type Quasar at z ∼ 2.1." Astrophysical Journal Letters 927, no. 2 (March 1, 2022): L24. http://dx.doi.org/10.3847/2041-8213/ac589f.

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Abstract We present optical spectroscopic and milliarcsecond-scale radio continuum observations of the quasar M1540–1453 (z em = 2.104 ± 0.002) that show associated H i 21 cm absorption at z abs = 2.1139. At subkiloparsec scales, the powerful radio source with 1.4 GHz luminosity of 5.9 × 1027 W Hz−1 shows Fanaroff–Riley class I morphology caused by the interaction with dense gas within 70 pc of the active galactic nucleus (AGN). Interestingly, while there are indications for the presence of absorption from low-ionization species like Fe ii, Si ii, and Si iii in the optical spectrum, the expected strong damped Lyα absorption is not detected at the redshift of the H i 21 cm absorber. In comparison to typical high-z quasars, the Lyα emission line is much narrower. The “ghostly” nature of the H i Lyα absorber partially covering the broad-line region of extent 0.05 pc and the detection of widespread H i 21 cm absorption covering the diffuse radio source (extent >425 pc) imply the presence of a large clumpy H i halo, which may have been blown by the jet–interstellar medium (ISM) interaction. Further observations are needed to confirm the ghostly nature of the Lyα absorber and obtain a better understanding of the role played by the jet–ISM interaction in shaping the radio morphology of this powerful AGN. The study showcases how joint radio and optical analysis can shed light on the gaseous environment and origin of radio morphology in AGNs at high redshifts, when these are still the assembly sites of giant galaxies.

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Grossová, Romana, Norbert Werner, Francesco Massaro, Kiran Lakhchaura, Tomáš Plšek, Krisztina Gabányi, Kamlesh Rajpurohit, et al. "Very Large Array Radio Study of a Sample of Nearby X-Ray and Optically Bright Early-type Galaxies." Astrophysical Journal Supplement Series 258, no. 2 (January 24, 2022): 30. http://dx.doi.org/10.3847/1538-4365/ac366c.

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Abstract Many massive early-type galaxies host central radio sources and hot X-ray atmospheres indicating the presence of radio-mechanical active galactic nucleus (AGN) feedback. The duty cycle and detailed physics of the radio-mode AGN feedback is still a matter of debate. To address these questions, we present 1–2 GHz Karl G. Jansky Very Large Array radio observations of a sample of the 42 nearest optically and X-ray brightest early-type galaxies. We detect radio emission in 41/42 galaxies. However, the galaxy without a radio source, NGC 499, has recently been detected at lower frequencies by the Low-Frequency Array. Furthermore, 27/42 galaxies in our sample host extended radio structures and 34/42 sources show environmental interactions in the form of X-ray cavities. We find a significant correlation between the radio flux density and the largest linear size of the radio emission and between the radio power and the luminosity of the central X-ray point source. The central radio spectral indices of the galaxies span a wide range of values, with the majority of the systems having steep spectra and the rest flat spectra. These results are consistent with AGN activity, where the central radio sources are mostly switched on, thus the duty cycle is very high. Seven out of 14 galaxies with pointlike radio emission (Fanaroff–Riley Class 0; FR 0) also show X-ray cavities indicating that, despite the lack of extended radio structures at 1–2 GHz, these AGNs do launch jets capable of inflating lobes and cavities.

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Snios, Bradford, Martijn De Vries, Paul E. J. Nulsen, Ralph P. Kraft, Aneta Siemiginowska, and Michael W. Wise. "Late-time X-ray observations of the transient source Cygnus A-2." Monthly Notices of the Royal Astronomical Society 511, no. 4 (February 17, 2022): 5817–22. http://dx.doi.org/10.1093/mnras/stac430.

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ABSTRACT We examine Chandra observations of the powerful Fanaroff–Riley class II (FR II) radio galaxy Cygnus A for an X-ray counterpart to the radio transient Cygnus A-2 that was first detected in 2011. Observations are performed using the High-Resolution Camera (HRC) instrument in order to spatially resolve Cygnus A-2 and the central active galactic nucleus (AGN) at a separation of 0.′′42. Simulated images are generated of the emission region, and radial profiles for the region of interest are extracted. A comparison between the simulations and observations reveals no X-ray detection of Cygnus A-2 to a 0.5–7.0 keV flux upper limit of $1.04 \times 10^{-12}\rm \, erg\, cm^{-2}\, s^{-1}$, or a rest-frame 2–10 keV luminosity of $8.6\times 10^{42}\rm \, erg\, s^{-1}$. We estimate the black hole mass of Cygnus A-2 based on our X-ray flux limit and find it to be consistent with a flaring black hole rather than a steadily accreting source. The HRC observations are additionally compared with archival Advanced CCD Imaging Spectrometer (ACIS) data from 2016 to 2017, and both the overall morphology and the flux limits of the AGN complex agree between the two data sets. This consistency is despite the pile-up effect in ACIS which was previously considered to bias the observed morphology of the AGN. The agreement between the data sets demonstrates the viability of utilizing the archival Chandra data of Cygnus A to analyse its AGN at an unprecedented level of precision.

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Capetti, A., M. Brienza, R. D. Baldi, G. Giovannini, R. Morganti, M. J. Hardcastle, H. J. A. Rottgering, G. F. Brunetti, P. N. Best, and G. Miley. "The LOFAR view of FR 0 radio galaxies." Astronomy & Astrophysics 642 (October 2020): A107. http://dx.doi.org/10.1051/0004-6361/202038671.

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We explore the low-frequency radio properties of the sources in the Fanaroff-Riley class 0 catalog (FR0CAT) as seen by the Low-Frequency ARray (LOFAR) observations at 150 MHz. This sample includes 104 compact radio active galactic nuclei (AGN) associated with nearby (z < 0.05) massive early-type galaxies. Sixty-six FR0CAT sources are in the sky regions observed by LOFAR and all of them are detected, usually showing point-like structures with sizes of ≲3–6 kpc. However, 12 FR 0s present resolved emission of low surface brightness, which contributes between 5% and 40% of the total radio power at 150 MHz, usually with a jetted morphology extending between 15 and 50 kpc. No extended emission is detected around the other FR 0s, with a typical luminosity limit of ≲5 × 1022 W Hz−1 over an area of 100 kpc × 100 kpc. The spectral slopes of FR 0s between 150 MHz and 1.4 GHz span a broad range (−0.7 ≲ α ≲ 0.8) with a median value of ᾱ ∼ 0.1; 20% of them have a steep spectrum (α ≳ 0.5), which is an indication of the presence of substantial extended emission confined within the spatial resolution limit. The fraction of FR 0s showing evidence for the presence of jets, by including both spectral and morphological information, is at least ∼40%. This study confirms that FR 0s and FR Is can be interpreted as two extremes of a continuous population of jetted sources, with the FR 0s representing the low end in size and radio power.

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Vagshette, Nilkanth D., Sachindra Naik, and Madhav K. Patil. "Cavities, shocks and a cold front around 3C 320." Monthly Notices of the Royal Astronomical Society 485, no. 2 (March 6, 2019): 1981–89. http://dx.doi.org/10.1093/mnras/stz476.

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Abstract We present results obtained from the analysis of a total of 110 ks of Chandra observations of the Fanaroff–Riley class II (FR II) radio galaxy 3C 320, located at the centre of a cluster of galaxies at redshift z = 0.342. A pair of X-ray cavities has been detected at an average distance of ∼38 kpc along the east and west directions, with cavity energy, age and total power equal to ∼7.7 × 1059 erg, ∼7 × 107 yr and ∼3.5 × 1044 erg s−1, respectively. The cooling luminosity within the cooling radius of ∼100 kpc was found to be Lcool ∼ 8.5 × 1043 erg s−1. Comparison of these two estimates (total cavity power and cooling luminosity) implies that the cavity power is sufficiently high to balance radiative loss. A pair of weak shocks has also been detected at distances of ∼47 and ∼76 kpc surrounding the radio bubbles. Using the observed density jumps of ∼1.8 and ∼2.1 at the shock locations along the east and west directions, we estimate the Mach numbers ($\mathcal {M}$) to be ∼1.6 and ∼1.8, respectively. A sharp surface-brightness edge was also detected at a relatively larger radius (∼80 kpc) along the south direction. The density jump at this surface-brightness edge was estimated to be ∼1.6 and it is probably due to the presence of a cold front in this cluster. The far-infrared luminosity yielded a star formation rate of 51 M⊙ yr−1, which is a quarter of the cooling rate ($\dot{M}$ ∼ 192 M⊙ yr−1).

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Seo, Jeongbhin, Dongsu Ryu, and Hyesung Kang. "A Simulation Study of Ultra-relativistic Jets. III. Particle Acceleration in FR-II Jets." Astrophysical Journal 944, no. 2 (February 1, 2023): 199. http://dx.doi.org/10.3847/1538-4357/acb3ba.

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Abstract We study the acceleration of ultra-high-energy cosmic rays (UHECRs) in Class II Fanaroff–Riley (FR-II) radio galaxies by performing Monte Carlo simulations for the transport, scattering, and energy change of CR particles injected into time-evolving jet flows that are realized through relativistic hydrodynamic simulations. Toward that end, we adopt physically motivated models for the magnetic field and particle scattering. By identifying the primary acceleration process among diffusive shock acceleration (DSA), turbulent shear acceleration (TSA), and relativistic shear acceleration (RSA), we find that CRs of E ≲ 1 EeV gain energy mainly through DSA in the jet‐spine flow and backflow containing many shocks and turbulence. After they attain E ≳ a few exaelectronvolts, CRs are energized mostly via RSA at the jet–backflow interface, reaching energies well above 1020 eV. TSA makes a relatively minor contribution. The time-asymptotic energy spectrum of escaping particles is primarily governed by the jet power, shifting to higher energies at more powerful jets. The UHECR spectrum fits well to a double power-law form, whose break energy, E break, corresponds to the size-limited maximum energy. It is close to d  / dE ∝ E − 0.5 below E break, while it follows d  / dE ∝ E − 2.6 above E break, decreasing more gradually than the exponential. The power-law slope of the high-energy end is determined by energy boosts via non-gradual shear acceleration across the jet–backflow interface and confinement by an elongated cocoon. We conclude that giant radio galaxies could be major contributors to the observed UHECRs.

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Grossová, R., N. Werner, K. Rajpurohit, F. Mernier, K. Lakhchaura, K. Gabányi, R. E. A. Canning, et al. "Powerful AGN jets and unbalanced cooling in the hot atmosphere of IC 4296." Monthly Notices of the Royal Astronomical Society 488, no. 2 (June 21, 2019): 1917–25. http://dx.doi.org/10.1093/mnras/stz1728.

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Abstract We present new Karl G. Jansky Very Large Array (VLA, 1.5 GHz) radio data for the giant elliptical galaxy IC 4296, supported by archival radio, X-ray (Chandra, and XMM–Newton) and optical (SOAR, and HST) observations. The galaxy hosts powerful radio jets piercing through the inner hot X-ray emitting atmosphere, depositing most of the energy into the ambient intracluster medium (ICM). Whereas the radio surface brightness of the A configuration image is consistent with a Fanaroff–Riley Class I system, the D configuration image shows two bright, relative to the central region, large (${\sim } 160\, \rm {kpc}$ diameter), well-defined lobes, previously reported by Killeen et al., at a projected distance $r\gtrsim 230\, \rm {kpc}$. The XMM–Newton image reveals an X-ray cavity associated with one of the radio lobes. The total enthalpy of the radio lobes is ${\sim }7\times 10^{59}\, \rm {erg}$ and the mechanical power output of the jets is ${\sim } 10^{44}\, \rm {erg\, s}^{-1}$. The jets are mildly curved and possibly rebrightened by the relative motion of the galaxy and the ICM. The lobes display sharp edges, suggesting the presence of bow shocks, which would indicate that they are expanding supersonically. The central entropy and cooling time of the X-ray gas are unusually low and the nucleus hosts a warm Hα + [$\rm{N\,{\small II}}$] nebula and a cold molecular CO disc. Because most of the energy of the jets is deposited far from the nucleus, the atmosphere of the galaxy continues to cool, apparently feeding the central supermassive black hole and powering the jet activity.

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Anglés-Castillo, Andreu, Manel Perucho, José María Martí, and Robert A. Laing. "On the deceleration of Fanaroff-Riley Class I jets: mass loading of magnetized jets by stellar winds." Monthly Notices of the Royal Astronomical Society, October 23, 2020. http://dx.doi.org/10.1093/mnras/staa3291.

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Abstract In this paper we present steady-state RMHD simulations that include a mass-load term to study the process of jet deceleration. The mass-load mimics the injection of a proton-electron plasma from stellar winds within the host galaxy into initially pair plasma jets, with mean stellar mass-losses ranging from 10−14 to 10−9 M⊙ yr−1. The spatial jet evolution covers ∼500 pc from jet injection in the grid at 10 pc from the jet nozzle. Our simulations use a relativistic gas equation of state and a pressure profile for the ambient medium. We compare these simulations with previous dynamical simulations of relativistic, non-magnetised jets. Our results show that toroidal magnetic fields can prevent fast jet expansion and the subsequent embedding of further stars via magnetic tension. In this sense, magnetic fields avoid a runaway deceleration process. Furthermore, when the mass-load is large enough to increase the jet density and produce fast, differential jet expansion, the conversion of magnetic energy flux into kinetic energy flux (i.e., magnetic acceleration), helps to delay the deceleration process with respect to non-magnetised jets. We conclude that the typical stellar population in elliptical galaxies cannot explain jet deceleration in classical FRI radio galaxies. However, we observe a significant change in the jet composition, thermodynamical parameters and energy dissipation along its evolution, even for moderate values of the mass-load.

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Fernini, Ilias. "VLA observations of 20 FR II radio sources at 8.4 GHz." Astrophysics and Space Science 364, no. 10 (October 2019). http://dx.doi.org/10.1007/s10509-019-3654-5.

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Abstract We report the last observational paper of hot spots for 20 Fanaroff-Riley class II (FR II) sources. These sources are part of a large sample of 98 FR II to study the unification scheme of FR II radio galaxies (RGs) and quasars (QSRs) using the hotspots (HSs) location and morphology. High-resolution VLA observations at 8.4 GHz were conducted for the whole sample. The investigation of HSs properties in FR II radio sources is essential for a better understanding of the dynamics related to the objects and their impact on the surrounding environment. HSs were classified into edged and recessed types, where the former is located at a radio lobe’s outer edge, and the latter is embedded within the lobe. The present sub-sample contains 12 RGs and 8 QSRs. Radio contour maps for each source were presented using the VLA in its A and B configurations. In total, we have identified 18 HSs for these 20 radio sources. The 12 RGs possess 8 edged HSs and 2 recessed HSs. The 8 QSRs possess 6 edged HSs and 2 recessed HSs. Out of the 14 edged HSs, RGs and QSRs possess $\sim57\%$∼57% and $\sim43\%$∼43%, respectively. A thorough morphological discussion of the 20 sources with their HSs is presented in the present work.

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Bruni, G., L. Bassani, M. Persic, Y. Rephaeli, A. Malizia, M. Molina, M. Fiocchi, et al. "IGR J18249–3243: a new GeV-emitting FR II and the emerging population of high energy radio galaxies." Monthly Notices of the Royal Astronomical Society, March 31, 2022. http://dx.doi.org/10.1093/mnras/stac865.

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Abstract The advent of new all-sky radio surveys such as the VLA Sky Survey (VLASS) and the Rapid ASKAP Continuum Survey (RACS), performed with the latest generation radio telescopes, is opening new possibilities on the classification and study of extragalactic γ-ray sources, specially the underrepresented ones like radio galaxies. In particular, the enhanced sensitivity (sub-mJy level) and resolution (a few arcsec) provides a better morphological and spectral classification. In this work, we present the reclassification of a Fermi/Large Area Telescope (LAT) source as a new Fanaroff-Riley II (FRII) radio galaxy from the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) sample found to emit at GeV energies. Through a broad-band spectral fitting from radio to γ-ray, we find that the commonly invoked jet contribution is not sufficient to account for the observed γ-ray flux. Our modeling suggests that the observed emission could mainly originate in the lobes (rather than in the radio core) by inverse Compton scattering of radio-emitting electrons off the ambient photon fields. In addition, we cross-correlated the latest generation radio surveys with a list of Fermi/LAT candidate misaligned AGN from the literature, finding four new radio galaxies with a double-lobed morphology. Additional four objects could be classified as such thanks to previous studies in the literature, for a total of nine new radio galaxies with GeV emission presented in this work. We foresee that further objects of this class might be found in the near future with the advent of the Square Kilometer Array (SKA), populating the GeV sky.

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Journal articles on the topic 'Fanaroff-Riley class I'

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